Clinical, radiographic and biochemical characteristics of adult hypophosphatasia

Hypophosphatasia Presenting as a Chronic Diffuse Pain Syndrome with Extra-Articular Calcifications

Hypophosphatasia is a rare genetic disease characterized by abnormal alkaline phosphatase activity and deficiency of bone and teeth mineralization. Hypophosphatasia is well known in pediatrics with typical presentations in children, but mild forms can also be present in adults and are difficult to detect. We present the case of a 50-year-old woman referred for pain management, with a previous diagnosis of fibromyalgia. The association of clinical features (diffuse pain syndrome, early dental loosening, personal history of two fractures with osteoporosis, and family history of osteoporosis) with radiographic (heterotopic calcifications of the yellow and interspinous lumbar ligaments) and biological (low levels of total alkaline phosphatase) indices was suggestive of hypophosphatasia, which was confirmed by genetic analysis. We review and discuss the association between hypophosphatasia, musculoskeletal pain, and calcium pyrophosphate deposition and the importance of raising the diagnosis of adult-onset hypophosphatasia when facing these two rheumatologic entities.

New Empirical Bayes Models to Jointly Analyze Multiple RNA-Sequencing Data in a Hypophosphatasia Disease Study

Hypophosphatasia is a rare inherited metabolic disorder caused by the deficiency of tissue-nonspecific alkaline phosphatase. More severe and early onset cases present symptoms of muscle weakness, diminished motor coordination, and epileptic seizures. These neurological manifestations are poorly characterized. Thus, it is urgent to discover novel differentially expressed genes for investigating the genetic mechanisms underlying the neurological manifestations of hypophosphatasia. RNA-sequencing data offer a high-resolution and highly accurate transcript profile. In this study, we apply an empirical Bayes model to RNA-sequencing data acquired from the spinal cord and neocortex tissues of a mouse model, individually, to more accurately estimate the genetic effects without bias. More importantly, we further develop two integration methods, weighted gene approach and weighted Z method, to incorporate two RNA-sequencing data into a model for enhancing the effects of genetic markers in the diagnostics of hypophosphatasia disease. The simulation and real data analysis have demonstrated the effectiveness of our proposed integration methods, which can maximize genetic signals identified from the spinal cord and neocortex tissues, minimize the prediction error, and largely improve the prediction accuracy in risk prediction.

The Effect of Asfotase Alfa on Plasma and Urine Pyrophosphate Levels and Pseudofractures in a Patient With Adult-Onset Hypophosphatasia

Hypophosphatasia (HPP) is an inherited disease caused by variants of the ALPL gene encoding tissue-nonspecific alkaline phosphatase. Adult-onset HPP (adult HPP), known as a mild form of HPP, develops symptoms involving osteomalacia after the age of 18 years. Asfotase alfa (AA) is a modulated recombinant human alkaline phosphatase (ALP) that has been established as a first-line therapy for severe forms of HPP, such as perinatal and infantile forms. We described a 64-year-old female who presented with pseudofractures in bilateral femur diaphyses and impaired mobility. Low serum ALP activity and a high concentration of urine phosphoethanolamine indicated the diagnosis of HPP, which was confirmed by the identification of a homozygous variant in the ALPL gene (c.319G > A; p.Val107Ile). An in vitro transfection experiment to measure the ALP activity of this novel variant protein was performed, resulting in 40% of the residual enzymatic activity compared with the wild type. AA was initiated to facilitate the union of pseudofracture and to improve mobility. After 6 months, radiographic images revealed the disappearance of fracture lines, and improvement of ambulatory ability was confirmed by the 6-minute walk test (525 to 606 m). The EQ-5D-5L index was also improved (0.757 to 0.895). Within a follow-up period, the levels of urine pyrophosphate corrected by urine creatinine (uPPi/Cre) declined in parallel with the level of plasma PPi (plasma PPi: 6.34 to 1.04 μM, uPPi/Cre: 226.8 to 75.4 nmol/mg). The beneficial effect of AA on pseudofracture healing in adult HPP was presented, although the application of AA should be restricted to patients exhibiting relatively severe manifestations. In addition, a novel pathogenic variant of the ALPL gene was identified with the supportive result of functional analysis. Furthermore, when monitoring patients with HPP treated with AA, uPPi/Cre might be a convenient substitute for plasma PPi, which requires immediate filtration after blood sampling. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Musculoskeletal and neurocognitive clinical significance of adult hypophosphatasia

Hypophosphatasia (HPP), also called Rathbun disease, is a rare genetic disorder that is caused by the loss-of-function mutation in the ALPL gene encoding tissue non-specific alkaline phosphatase. Doctor Rathbun first described the case of a 3-week-old infant who presented with severe osteopenia, rickets, and multiple radiographic fractures, and died shortly after of epileptic seizure and respiratory distress. The term "hypophosphatasia" was coined as the patients' alkaline phosphatase levels were significantly low. Since then, our understanding of HPP has evolved, and now we appreciate causative genetic mutation and the broad spectrum of clinical presentation depending on the age of onset, severity, and skeletal involvement: perinatal, infantile, childhood, adult and odontohypophosphatasia. The new development of enzyme replacement with asfostase alfa has saved the lives of severe form of hypophosphatasia. However, it is still unclear and remains challenging how to manage adult HPP that often presents with mild and non-specific symptoms such as muscle pain, joint stiffness, fatigue, anxiety, or low bone mass, which are common in the general population and not necessarily attributed to HPP. In this review, we will present 3 unique cases of adult HPP and discuss the pathophysiology, clinical presentation particularly neuromuscular and neurocognitive symptoms and management of adult HPP.

Impact of Restricted Phosphorus, Calcium-adjusted Diet on Musculoskeletal and Mental Health in Hypophosphatasia

Context

Impairments in musculoskeletal and mental health are common in adults with Hypophosphatasia (HPP). Restricted phosphorus intake has been suggested to positively affect symptoms in HPP, but there is a lack of interventional evidence.

Objective

This work aimed to evaluate the effect of a phosphorus-restricted, calcium-adjusted diet on musculoskeletal and mental health in HPP.

Methods

A prospective, noncontrolled, single-center interventional study (NuSTEPS II) was conducted among outpatients at the Osteology Department, University of Wuerzburg, Germany. A total of 26 adults with an established HPP diagnosis received a standardized diet with a defined daily intake of phosphorus (1160-1240 mg/d) and calcium (870-930 mg/d) over 8 weeks. Main outcome measures were functional testing and patient-reported outcome measures.

Results

At 8 weeks, significant improvements were observed in usual gait speed (P = .028) and the chair-rise test (P = .019), while no significant changes were seen in the 6-minute walk test (P = .468) and the timed up-and-go test (P = .230). Pain was not significantly reduced according to the visual analog scale (VAS) (P = .061), pain subscale of the 36-Item Short-Form Health Survey (SF-36) (P = .346), and Pain Disability Index (P = .686). Further, there was a significant improvement in the SF-36 vitality subscale (P = .022) while all other subscales as well as the Lower Extremity Functional Scale (P = .670) and the Fatigue Assessment Scale (P = .392) did not change significantly. Adjustments of mineral intake were not associated with relevant alterations regarding the intake of energy and energy-supplying nutrients or body composition.

Conclusion

Adjusting phosphorus and calcium intake may positively affect individual symptoms in adults with HPP, but overall clinical effectiveness regarding major issues like pain and endurance appears limited.

Musculoskeletal pain and muscular weakness as the main symptoms of adult hypophosphatasia in a Spanish cohort: clinical characterization and identification of a new ALPL gene variant

INTRODUCTION

Hypophosphatasia (HPP) is a rare inherited disorder, caused by mutations in the alkaline phosphatase (ALPL) gene, which encodes for the tissue non-specific alkaline phosphatase (TNSALP) isoform of alkaline phosphatase (ALP). Adult HPP is one of the mild forms that presents with unspecific signs such as osteopenia, osteomalacia and muscle involvement. Our purpose was to identify and characterize possibly misdiagnosed adult HPP patients at a clinical and biochemical level.

MATERIAL AND METHODS

At the laboratory of Miguel Servet University Hospital we retrospectively reviewed serum ALP levels in adults over a 48-month period. The clinical records of individuals with consistently low ALP levels were reviewed to exclude secondary causes. Those with persistent hypophosphatasemia were screened for symptoms of HPP. The study participants were evaluated at biochemical and genetic levels.

RESULTS

We identified 705 ALP determinations (out of 384,000 processed) in 589 patients below the reference range (30 U/l). Only 21 patients with clinical signs and symptoms of HPP were selected for genetic testing. Finally, only 12 patients participated in the study, 83.3% of whom (10/12) harbored a pathogenic or likely pathogenic variant in a heterozygous state. The major symptoms of our cohort were the presence of musculoskeletal pain (100% of patients) and muscular weakness (83.3% patients).

CONCLUSION

Mild HPP patients presenting with diffuse symptoms such as musculoskeletal pain may be undiagnosed or misdiagnosed as osteoporosis patients by routine diagnosis. It is important to identify these individuals, to avoid inappropriate treatment with antiresorptive drugs.

Reducing diagnostic delay in hypophosphatasia: a case series of 14 patients presenting to general rheumatology

OBJECTIVES

Hypophosphatasia (HPP) is a rare genetic metabolic bone disease that can cause chronic pain and fractures. Its hallmark is a persistently low serum ALP. HPP is now recognised by many osteoporosis specialists, but other specialists, such as rheumatologists and primary care physicians, may be less aware of this condition, causing diagnostic delay and possible harm to these patients. Our objective was to highlight features that can reduce this delay.

METHODS

We retrospectively analysed 14 patients that presented with musculoskeletal pain to general rheumatology clinic at St. George's Hospital and were subsequently diagnosed with HPP.

RESULTS

Median diagnostic delay was 13 years. All patients had an ALP below reference range for age and gender, with lowest mean ALP of 16 IU/L. All but one patient were women with median age of 51 years. Most common presentation was peripheral joint pain in 85.7% of patients. This was due to early-onset CPPD (calcium pyrophosphate deposition disease) in 71.4% of patients, osteoarthritis in 50%, or bursitis in 50%. Axial pain was reported in 64% of patients due to osteoarthritis or spinal stenosis. Fifty percent of patients had a history of long bone pain. Fifty percent had previous fracture(s). A total of 28.6% of patients had psoriatic arthritis, of which 1 patient had spondyloarthropathy, and 4 patients also had enthesitis.

CONCLUSION

Patients with HPP can present to rheumatology with musculoskeletal pain, and if a persistently low ALP is confirmed, this may reduce the diagnostic delay of this rare disease. Similar to other rheumatologic patients, musculoskeletal pain in HPP was noted in peripheral joints and in the spine with almost a third of patients having psoriatic arthritis. Pain was also noted in the long bones, a feature consistent with metabolic bone disease. The diagnosis of HPP was also more likely in those patients with a personal or family history of dental disease or arthritis.

Hypophosphatasia: from birth to adulthood

Hypophosphatasia (HPP) is an inherited disease caused by a low activity of tissue-nonspecific alkaline phosphatase, a hydrolase that removes phosphate groups from many molecules. Decreased alkaline phosphatase activity leads to the accumulation of three main metabolites, i.e., pyridoxal 5´-phosphate (PLP), inorganic pyrophosphate (PPi), and phosphoethanolamine. Impairment in PLP dephosphorylation induces seizures, while PPi accumulation inhibits bone mineralization. Clinically, HPP has a wide spectrum of presentations, ranging from neonatal death to an apparent lack of symptoms. This disease is classified into six subtypes according to the age at onset of first signs or symptoms. The clinical manifestations of the disease include rickets-like bone changes, bone demineralization, fragility fractures, reduced muscular strength, chest deformity, pulmonary hypoplasia, nephrolithiasis, nephrocalcinosis, and chondrocalcinosis. Treatment of HPP consists of enzyme replacement therapy. Before this therapy was approved, treatment was palliative and associated with high morbidity and mortality. Asfotase alfa has changed the prognosis of the disease by reducing bone deformity and improving bone mineralization, lung function, and muscle weakness, among other benefits. In adults, teriparatide and anti-sclerostin antibody have been used off-label in selected cases, demonstrating benefit in accelerating fracture healing and in concomitant treatment of osteoporosis. This review summarizes the main aspects of HPP and identifies the particularities of the disease in adult patients.

Radial HR-pQCT and Finite Element Analysis in HPP Patients are Superior in Identifying Susceptibility to Fracture-Associated Skeletal Affections Compared to DXA and Laboratory Tests

Hypophosphatasia (HPP) is an inborn disease that causes a rare form of osteomalacia, a mineralization disorder affecting mineralized tissues. Identification of patients at high risk for fractures or other skeletal manifestations (such as insufficiency fractures or excessive bone marrow edema) by bone densitometry and laboratory tests remains clinically challenging. Therefore, we examined two cohorts of patients with variants in the ALPL gene grouped by bone manifestations. These groups were compared by means of bone microarchitecture using high-resolution peripheral quantitative computed tomography (HR-pQCT) and simulated mechanical performance utilizing finite element analysis (FEA). Whereas the incidence of skeletal manifestations among the patients could not be determined by dual energy X-ray absorptiometry (DXA) or laboratory assessment, HR-pQCT evaluation showed a distinct pattern of HPP patients with such manifestations. Specifically, these patients had a pronounced loss of trabecular bone mineral density, increased trabecular spacing, and decreased ultimate force at the distal radius. Interestingly, the derived results indicate that the non-weight-bearing radius is superior to the weight-bearing tibia in identifying deteriorated skeletal patterns. Overall, the assessment by HR-pQCT appears to be of high clinical relevance due to the improved identification of HPP patients with an increased risk for fractures or other skeletal manifestations, especially at the distal radius.

Clinical and Genetic Characteristics of Hypophosphatasia in Chinese Adults

Hypophosphatasia (HPP) is an inherited disease caused by ALPL mutation, resulting in decreased alkaline phosphatase (ALP) activity and damage to bone and tooth mineralization. The clinical symptoms of adult HPP are variable, making diagnosis challenging. This study aims to clarify the clinical and genetic characteristics of HPP in Chinese adults. There were 19 patients, including 1 with childhood-onset and 18 with adult-onset HPP. The median age was 62 (32-74) years and 16 female patients were involved. Common symptoms included musculoskeletal symptoms (12/19), dental problems (8/19), fractures (7/19), and fatigue (6/19). Nine patients (47.4%) were misdiagnosed with osteoporosis and six received anti-resorptive treatment. The average serum ALP level was 29.1 (14-53) U/L and 94.7% (18/19) of patients had ALP levels below 40 U/L. Genetic analysis found 14 ALPL mutations, including three novel mutations-c.511C>G (p.His171Ala), c.782C>A (p.Pro261Gln), and 1399A>G (p.Met467Val). The symptoms of two patients with compound heterozygous mutations were more severe than those with heterozygous mutations. Our study summarized the clinical characteristics of adult HPP patients in the Chinese population, expanded the spectrum of pathogenic mutations, and deepened clinicians' understanding of this neglected disease.

Diagnostic Approach to Patients with Low Serum Alkaline Phosphatase

Increased serum levels of alkaline phosphatase (ALP) are widely recognized as a biochemical marker of many disorders affecting the liver or bone. However, the approach for patients with low ALP phosphatase is not well-established. Low serum ALP is an epiphenomenon of many severe acute injuries and diseases. Persistently low serum ALP may be secondary to drug therapy (including antiresorptives) or a variety of acquired disorders, such as malnutrition, vitamin and mineral deficiencies, endocrine disorders, etc. Hypophosphatasia, due to pathogenic variants of the ALPL gene, which encodes tissue non-specific ALP, is the most common genetic cause of low serum ALP. Marked bone hypomineralization is frequent in severe pediatric-onset cases. However, adult forms of hypophosphatasia usually present with milder manifestations, such as skeletal pain, chondrocalcinosis, calcific periarthritis, dental problems, and stress fractures. The diagnostic approach to these patients is discussed. Measuring several ALP substrates, such as pyrophosphate, pyridoxal phosphate, or phosphoethanolamine, may help to establish enzyme deficiency. Gene analysis showing a pathogenic variant in ALPL may confirm the diagnosis. However, a substantial proportion of patients show normal results after sequencing ALPL exons. It is still unknown if those patients carry unidentified mutations in regulatory regions of ALPL, epigenetic changes, or abnormalities in other genes.

A low serum alkaline phosphatase may signal hypophosphatasia in osteoporosis clinic patients

Low serum alkaline phosphatase (ALP) was found in 9% of patients attending an osteoporosis clinic, 0.6% of hospital patients, and 2/22 with an atypical femoral fracture. Hypophosphatasia was diagnosed in 3% of osteoporosis clinic patients with low ALP. Low ALP is a screening tool for hypophosphatasia, a condition potentially aggravated by antiresorptive therapy.

INTRODUCTION

Hypophosphatasia (HPP) is an inherited disorder associated with impaired primary mineralisation of osteoid (osteomalacia). HPP may be misdiagnosed as osteoporosis, a reduction in the volume of normally mineralized bone. Both illnesses may result in fragility fractures, although stress and atypical fractures are more common in HPP. Antiresorptive therapy, first-line treatment for osteoporosis, is relatively contraindicated in HPP. Misdiagnosis and mistreatment can be avoided by recognising a low serum alkaline phosphatase (ALP). Our aim was to determine the prevalence of a low ALP (< 30 IU/L) in patients attending an osteoporosis clinic, in a hospital-wide setting, and in a group of patients with atypical femoral fractures (AFF).

METHODS

This was a retrospective study of patients attending an osteoporosis clinic at a tertiary hospital during 8 years (2012-2020). Patients were categorised into those with a transiently low ALP, those with low ALP on ≥ 2 occasions but not the majority of measurements, and those with a persistently low ALP. ALP levels were also assessed in hospital-wide records and a group of patients with AFF.

RESULTS

Of 1839 patients attending an osteoporosis clinic, 168 (9%) had ≥ 1 low ALP, 50 (2.7%) had low ALP for ≥ 2 months, and seven (0.4%) had persistently low ALP levels. HPP was diagnosed in five patients, four of whom had persistently low ALP levels. The prevalence of HPP was 0.3% in the osteoporosis clinic and 3% in patients with ≥ 1 low ALP. Low ALP occurred in 0.6% of all hospital patients and 2/22 with AFF.

CONCLUSION

Persistently low ALP in osteoporosis clinic attendees is easy to identify and signals the possibility of hypophosphatasia, a condition that may be mistaken for osteoporosis and incorrectly treated with antiresorptive therapy.

Osteomalacia

Osteomalacia with characteristic histomorphometric, radiographic, laboratory and clinical features is a prominent syndrome of disturbed bone mineralisation in adulthood. From an etiological point of view, osteomalacia is usually caused by substrate (calcium, phosphate) deficiency, presence of excess mineralization inhibitors or deficiency or ineffectivness of mineralization facilitator (vitamin D). In proportion to the high number of congenital and acquired causes of osteomalacia, its clinical and laboratory picture is heterogeneous and rarely fully expressed. The treatment of a particular case is determined by the cause of osteomalacia and may (but does not necessarily) include correction of the underlying disease, administration of calcium and various forms of vitamin D, as well as orthopaedic interventions. For some of the hereditary forms, biological or replacement therapy is prospectively available. The article attempts to cover the whole range of osteomalacia variants, mentioning a fact discussed only in recent years - the occurrence of oligosymptomatic, incompletely expressed forms.

Proposing a clinical algorithm for better diagnosis of hypophosphatasia in resource-limiting situations

Early diagnosis of hypophosphatasia (HPP) is challenging. Here, we propose to broaden the diagnostic criteria of HPP by reviewing published data on BMD and fractures in HPP patients. Non-osteoporotic fractures and higher than normal lumbar BMD were recurrent in HPP patients and could be included as diagnostic criteria. HPP is a genetic disorder caused by autosomal recessive or dominant loss-of-function mutations in the ALPL gene that encodes for tissue-nonspecific alkaline phosphatase (TNSALP). Expressive genetic heterogeneity and varying severity of TNSALP deficiency lead to a wide-ranging presentation of skeletal diseases at different ages that coupled with HPP's rarity and limitation of biochemical and mutational studies present serious hurdles to early diagnosis and management of HPP. To widen the scope of HPP diagnosis, we assessed the possibility of areal bone mineral density (BMD) as an additional clinical feature of this disease. PubMed, Web of Science, and ScienceDirect were searched with the following keywords: ("Hypophosphatasia OR HPP") AND ("Bone Mineral Density OR BMD") AND "Human". Studies and case reports of subjects with age ≥ 18 years and having BMD data were included. We pooled data from 25 publications comprising 356 subjects (90 males, 266 females). Only four studies had a control group. Biochemical hallmarks, pyridoxal 5'-phosphate (PLP) and phosphoethanolamine (PEA), were reported in fifteen and six studies, respectively. Twenty studies reported genetic data, nineteen studies reported non-vertebral fractures, all studies reported lumbar spine (LS) BMD, and nineteen reported non-vertebral BMD. Higher than normal and normal BMD at LS were reported in three and two studies, respectively. There was marked heterogeneity in BMD at the non-vertebral sites. Higher than normal or normal LS BMD in an adult with minimal or insufficient fractures, pseudofractures, non-healing fractures, fragility fractures, and stress fractures may be included in the diagnostic protocol of HPP. However, genetic testing is recommended for a definitive diagnosis.

Biochemical and clinical manifestations in adults with hypophosphatasia: a national cross-sectional study

Hypophosphatasia (HPP) is a rare disease affecting bone mineralization. Adults with HPP have an increased occurrence of low-energy fractures, which cannot be explained by reduced bone mass assessed by dual energy X-ray absorptiometry. The bone phenotype in adults with HPP requires further studies investigating bone strength and bone structural parameters.

INTRODUCTION

Hypophosphatasia (HPP) is a rare inherited disorder of bone and mineral metabolism, characterized by broad-ranging clinical manifestations and severity. However, studies investigating the clinical spectrum in adults with HPP compared to a control group are scarce. The aim of this study was to evaluate biochemical and clinical characteristics as well as bone health in a Danish cohort of adults with HPP.

METHODS

We conducted a cross-sectional study assessing biochemical parameters, fracture prevalence, bone mineral density (BMD), bone turnover markers, physical performance and pain characteristics in 40 adults with HPP and 40 sex-, age-, BMI- and menopausal status-matched healthy controls.

RESULTS

Patients with HPP had a significantly higher prevalence of non-vertebral, low-energy fractures (p =  < 0.001). BMD at the lumbar spine, total hip, femoral neck, forearm and whole body did not differ between the groups. Low levels of the bone-specific alkaline phosphatase correlated significantly with higher BMD at the lumbar spine and femoral neck in both groups. The bone formation marker N-terminal propeptide of type 1 procollagen was significantly lower in patients with HPP than healthy controls (p = 0.006). Adults with HPP had significantly reduced walking capability (p =  < 0.001) and lower body strength (p =  < 0.001). Chronic pain was significantly more prevalent in adults with HPP than the control group (p = 0.029).

CONCLUSIONS

The increased occurrence of low-energy fractures in adults with HPP is not explained by low BMD. Adults with HPP have reduced physical performance when compared with healthy controls.

Different Dental Manifestations in Sisters with the Same ALPL Gene Mutation: A Report of Two Cases

Hypophosphatasia (HPP) is an inherited disease caused by mutation of the alkaline phosphatase (ALPL) gene in an autosomal dominant or an autosomal recessive manner. The main symptoms of HPP are bone hypomineralization and early exfoliation of the primary teeth. Some of the mutations identified in autosomal dominant families are reported to have dominant negative effects. In addition, the penetrance can vary among patients with the same variant even within the same family, resulting in various phenotypes of systemic symptoms. However, differences in dental symptoms between patients with HPP and carriers with the same ALPL variant have not been reported. Herein, we report on two sisters who had the same heterozygous ALPL variant with dominant negative effects. The older sister had bone and dental symptoms and was diagnosed with childhood HPP. In contrast, the younger sister was a carrier with no bone and dental symptoms. It can be inferred that this phenomenon was caused by the difference in penetrance. This case revealed that carriers with the ALPL mutation may have no dental symptoms characteristic of HPP. Because HPP is sometimes progressive, it is very important to carefully monitor carriers to detect the possible onset of dental and systemic symptoms.

Anabolic actions of parathyroid hormone in a hypophosphatasia mouse model

Hypophosphatasia, the rare heritable disorder caused by TNAP enzyme mutations, presents wide-ranging severity of bone hypomineralization and skeletal abnormalities. Intermittent PTH (1-34) increased long bone volume in Alpl^-/- mice but did not alter the skull phenotype. PTH may have therapeutic value for adults with TNAP deficiency-associated osteoporosis.

INTRODUCTION

Hypophosphatasia is the rare heritable disorder caused by mutations in the tissue non-specific alkaline phosphatase (TNAP) enzyme leading to TNAP deficiency. Individuals with hypophosphatasia commonly present with bone hypomineralization and skeletal abnormalities. The purpose of this study was to determine the impact of intermittent PTH on the skeletal phenotype of TNAP-deficient Alpl^-/- mice.

METHODS

Alpl-/- and Alpl+/+ (wild-type; WT) littermate mice were administered PTH (1-34) (50 µg/kg) or vehicle control from days 4 to 12 and skeletal analyses were performed including gross measurements, micro-CT, histomorphometry, and serum biochemistry.

RESULTS

Alpl^-/- mice were smaller with shorter tibial length and skull length compared to WT mice. Tibial BV/TV was reduced in Alpl^-/- mice and daily PTH (1-34) injections significantly increased BV/TV and BMD but not TMD in both WT and Alpl^-/- tibiae. Trabecular spacing was not different between genotypes and was decreased by PTH in both genotypes. Serum P1NP was unchanged while TRAcP5b was significantly lower in Alpl^-/- vs. WT mice, with no PTH effect, and no differences in osteoclast numbers. Skull height and width were increased in Alpl^-/- vs. WT mice, and PTH increased skull width in WT but not Alpl^-/- mice. Frontal skull bones in Alpl^-/- mice had decreased BV/TV, BMD, and calvarial thickness vs. WT with no significant PTH effects. Lengths of cranial base bones (basioccipital, basisphenoid, presphenoid) and lengths of synchondroses (growth plates) between the cranial base bones, plus bone of the basioccipitus, were assessed. All parameters were reduced (except lengths of synchondroses, which were increased) in Alpl^-/- vs. WT mice with no PTH effect.

CONCLUSION

PTH increased long bone volume in the Alpl^-/- mice but did not alter the skull phenotype. These data suggest that PTH can have long bone anabolic activity in the absence of TNAP, and that PTH may have therapeutic value for individuals with hypophosphatasia-associated osteoporosis.

Urine phosphoethanolamine is a specific biomarker for hypophosphatasia in adults

OBJECTIVES

We investigated the utility of urine phosphoethanolamine (PEA) as a marker to aid in diagnosing and/or confirming hypophosphatasia (HPP) in adults and for monitoring patients on enzyme replacement therapy (ERT).

METHODS

Data was collected from seventy-eight adults who were referred to the Vanderbilt Program for Metabolic Bone Disease for evaluation of a possible or confirmatory HPP diagnosis between July 2014 through December 2019. Fifty-nine patients were diagnosed with HPP and nineteen were excluded from a diagnosis of HPP. The urine PEA results of those patients with a confirmed diagnosis of HPP and those patients with a diagnosis of HPP excluded were captured and compared to other laboratory and clinical parameters consistent with HPP, including alkaline phosphatase (ALP) activity, plasma pyridoxal 5'-phosphate (PLP), the presence of musculoskeletal abnormalities, and genetic testing for pathogenic mutations in ALPL.

RESULTS

Initial urine PEA values in patients in our HPP cohort and not on ERT were significantly higher (median = 150.0 nmol/mg creatinine, IQR = 82.0-202.0) compared patients in our HPP negative group (median 18.0 nmol/mg creatinine, IQR = 14.0-30.0, p < 0.0001) and higher than patients on ERT (median 65.0 nmol/mg creatinine, IQR = 45.3-79.8). Patients who began ERT had a decline in urine PEA levels after treatment with a mean decrease of 68.1 %. Plasma ALP levels were significantly lower in the group of patients with HPP and not on ERT group (median = 24.0 U/L, IQR = 15.0-29.50) compared to the patients without HPP (median = 45.50 U/L, IQR = 34.0-62.0;) and plasma PLP levels were significantly higher in the HPP non-ERT group (median = 284.0 nmol/L, IQR = 141.0-469.4) compared to the patients without HPP (median = 97.5 nmol/L, IQR = 43.7-206.0;). The area under the curve (AUC) of urine PEA, ALP, and PLP to distinguish between HPP and non-HPP patients is 0.968, 0.927 and 0.781, respectively, in our cohort. Urine PEA had 100 % specificity (95 % CI of 83.2 % to 100.0 %) for diagnosing HPP at a value >53.50 nmol/mg creatinine with a sensitivity of 88.4 %; 95%CI 75.5 to 94.9 %. ALP had a 100 % specificity (95 % CI of 82.4 % to 100.0 %) for diagnosing HPP at a value <30.5 U/L with a sensitivity of 77.2 %; (95%CI 64.8 to 86.2 %). PLP had a 100 % specificity (95 % CI of 81.6 % to 100.0 %) for diagnosing HPP at a value >436 nmol/L with a sensitivity of 26.9 %; (95%CI 16.8 to 40.3 %). The most common pathogenic or likely pathogenic mutations in our cohort were c.1250A>G (p.Asn417Ser), c.1133A>T (p.Asp378Val), c.881A>C (p.Asp294Ala), c.1171C>T (p.Arg391Cys), and c.571G>A, (p.Glu191Lys).

CONCLUSIONS

Urine PEA is a promising diagnostic and confirmatory marker for HPP in patients undergoing investigation for HPP. Urine PEA also has potential use as a marker to monitor ERT compliance. Future studies are necessary to evaluate the association between PEA levels and clinical outcomes.

Clinical profiles of treated and untreated adults with hypophosphatasia in the Global HPP Registry

Background

The clinical signs and symptoms of hypophosphatasia (HPP) can manifest during any stage of life. The age at which a patient’s symptoms are reported can impact access to targeted treatment with enzyme replacement therapy (asfotase alfa), as this treatment is indicated for patients with pediatric-onset HPP in most countries. As such, many patients reported to have adult-onset HPP typically do not receive treatment. Comparison of the disease in treated and untreated adult patients is confounded by the approved indication. To avoid this confounding factor, a comparison between baseline disease manifestations prominent among treated versus untreated adult patients was limited to those with pediatric-onset HPP using data collected from the Global HPP Registry. The hypothesis was that treated adults will have a greater disease burden at baseline than untreated adults. The analysis of disease manifestations in adults with adult-onset HPP was conducted separately.

Results

A total of 398 adults with HPP were included; 213 with pediatric-onset (114 treated, 99 untreated) and 141 with adult-onset HPP (2 treated and 139 untreated). The treated, pediatric-onset patients were more likely to have a history of pain (prevalence ratio [PR]: 1.3, 95% confidence interval [CI] 1.1, 1.4), skeletal (PR: 1.3, 95% CI 1.1, 1.6), constitutional/metabolic (PR: 1.7, 95% CI 1.3, 2.0), muscular (PR: 1.8, 95% CI 1.4, 2.1) and neurological (PR: 1.7, 95% CI 1.1, 2.3) manifestations of HPP, and also had poorer measures for health-related quality of life, pain, and disability compared with untreated pediatric-onset patients. In patients with adult-onset HPP, the most frequent signs and symptoms were chronic bone pain (52.5%), dental manifestations (42.6%), fatigue (23.4%), recurrent fractures or pseudofractures (22.0%), and generalized body pain (22.0%).

Conclusions

Along with the more classical skeletal signs and symptoms, pain, muscular, and constitutional/metabolic manifestations are common in adults with HPP, regardless of age of disease onset, highlighting a full spectrum of HPP manifestations.

Bone-microarchitecture and bone-strength in a sample of adults with hypophosphatasia and a matched reference population assessed by HR-pQCT and impact microindentation

BACKGROUND

Hypophosphatasia (HPP) is an autosomal recessive or dominate disease affecting bone mineralization, and adults with HPP are in risk to develop metatarsal stress fractures and femoral pseudofractures. Given to the scarce data on the bone quality and its association to the fracture risk in adults with HPP, this study aimed to evaluate bone turnover, bone strength and structure in adults with HPP.

METHODS

In this cross-sectional study, we included 14 adults with genetically verified HPP and 14 sex-, age-, BMI-, and menopausal status-matched reference individuals. We analyzed bone turnover markers, and measured bone material strength index (BMSi) by impact microindentation. Bone geometry, volumetric density and bone microarchitecture as well as failure load at the distal radius and tibia were evaluated using a second-generation high-resolution peripheral quantitative computed tomography system.

RESULTS

Bone turnover markers did not differ between patients with HPP and reference individuals. BMSi did not differ between the groups (67.90 [63.75-76.00] vs 65.45 [58.43-69.55], p = 0.149). Parameters of bone geometry and volumetric density did not differ between adults with HPP and the reference group. Patients with HPP had a tendency toward higher trabecular separation (0.664 [0.613-0.724] mm vs 0.620 [0.578-0.659] mm, p = 0.054) and inhomogeneity of trabecular network (0.253 [0.235-0.283] mm vs 0.229 [0.208-0.252] mm, p = 0.056) as well as lower trabecular bone volume fraction (18.8 [16.4-22.7] % vs 22.8 [20.6-24.7] %, p = 0.054) at the distal radius. In addition, compound heterozygous adults with HPP had a significantly higher cortical porosity at the distal radius than reference individuals (1.5 [0.9-2.2] % vs 0.7 [0.6-0.7] %, p = 0.041).

CONCLUSIONS

BMSi is not reduced in adults with HPP. Increased cortical porosity may contribute to the occurrence of femoral pseudofractures in compound heterozygous adults with HPP. However, further studies investigating larger cohorts of adults with HPP using methods of bone histomorphometry are recommended to adequately assess the bone quality in adults with HPP.

Biochemical algorithm to identify individuals with ALPL variants among subjects with persistent hypophosphatasaemia

Background

Hypophosphatasia (HPP) is a rare and underdiagnosed condition characterized by deficient bone and teeth mineralization. The aim of this study was first, to evaluate the diagnostic utility of employing alkaline phosphatase (ALP) threshold levels to identify adults with variants in ALPL among individuals with persistently low ALP levels and second, to determine the value of also including its substrates (serum pyridoxal-5′-phosphate—PLP—and urinary phosphoetanolamine-PEA) for this purpose in order to create a biochemical algorithm that could facilitate the diagnostic work-up of HPP.

Results

The study population comprised 77 subjects with persistent hypophosphatasaemia. They were divided into two groups according to the presence (+GT) or absence (−GT) of pathogenic ALPL variants: 40 +GT and 37 −GT. Diagnostic utility measures were calculated for different ALP thresholds and Receiver Operating Characteristic (ROC) curves were employed to determine PLP and PEA optimal cut-off levels to predict the presence of variants. The optimal threshold for ALP was 25 IU/L; for PLP, 180 nmol/L and for PEA, 30 µmol/g creatinine. Biochemical predictive models were assessed using binary logistic regression analysis and bootstrapping machine learning technique and results were then validated. For ALP < 25 UI/L (model 1), the area under curve (AUC) and the 95% confidence intervals (CI) was 0.68 (95% CI 0.63–0.72) and it improved to 0.87 (95% CI 0.8–0.9), when PEA or PLP threshold levels were added (models 2 and 3), reaching 0.94 (0.91–0.97) when both substrates were included (model 4). The internal validation showed that the addition of serum PLP threshold levels to the model just including ALP improved significantly sensitivity (S) and negative predictive value (NPV) − 100%, respectively- with an accuracy (AC) of 93% in comparison to the inclusion of urinary PEA (S: 71%; NPV 75% and AC: 79%) and similar diagnostic utility measures as those observed in model 3 were detected when both substrates were added.

Conclusions

In this study, we propose a biochemical predictive model based on the threshold levels of the main biochemical markers of HPP (ALP < 25 IU/L and PLP > 180 nmol/L) that when combined, seem to be very useful to identify individuals with ALPL variants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13023-022-02253-5.

Young woman with hypophosphatasia: A case report

Hypophosphatasia is a rare inherited disease defined by teeth and bone mineralization impairment leading to depletion of tissue non‐specific alkaline phosphatase. We define a young woman diagnosed with hypophosphatasia (after several times alkaline phosphatase levels were low) was discovered following femoral fracture. A 30‐year‐old woman who presented for a history of early permanent teeth loss during the last 5 years and HPP‐like symptoms in family history and bone radiograph verified bowing, deficient mineralization, and symmetrical subtrochanteric stress fractures of femurs was referred to our clinic for further management. Blood test findings defined raised phosphorus levels on two occasions at 6.2 and 5.7 mg/dl and insufficient 25‐hydroxy vitamin D level. HPP early diagnosis and adequate treatment, depending on the clinical symptoms along with laboratory tests, could be effective in decreasing the suffering of the disease and side effects.

Evaluation of alveolar bone hypomineralization in pediatric hypophosphatasia using orthopantomography

Hypophosphatasia (HPP) is a metabolic disease characterized by impaired bone mineralization and early exfoliation of primary teeth. This study was performed to develop a method for quantitatively evaluating alveolar bone hypomineralization using orthopantomographic images. Alveolar bone density was defined according to the pixel values and corrected by brightness shown by an indicator applied to the orthopantomographic device. Images of 200 healthy subjects (aged 2-15 years) were classified into five age groups. The corrected pixel values were significantly lower in the younger group than in those aged 14-15 years (2-4, 5-7, and 8-10 years versus 14-15 years: P < 0.0001, 11-13 years versus 14-15 years: P < 0.01). Orthopantomographic images of 17 patients with HPP were evaluated. The corrected pixel values of three-fourths of the patients with odonto type HPP were lower than the mean values of the healthy group. One-third of patients treated with enzyme replacement therapy showed higher corrected pixel values than the healthy group. Our results suggest that odonto type HPP without skeletal problems is occasionally accompanied by hypomineralization of alveolar bone and that alveolar bone hypomineralization in patients with severe HPP is possibly improved by enzyme replacement therapy.

Hypophosphatasia

Hypophosphatasia (HPP) is an inherited metabolic disease caused by loss-of-function mutations in the tissue non-specific alkaline phosphatase (TNAP) gene. Reduced activity of TNAP leads to the accumulation of its substrates, mainly inorganic pyrophosphate and pyridoxal-5′-phosphate, metabolic aberrations that largely explain the musculoskeletal and systemic features of the disease. More than 400 ALPL mutations, mostly missense, are reported to date, transmitted by either autosomal dominant or recessive mode. Severe disease is rare, with incidence ranging from 1:100,000 to 1:300,000 live births, while the estimated prevalence of the less severe adult form is estimated to be between 1:3100 to 1:508, in different countries in Europe. Presentation largely varies, ranging from death in utero to asymptomatic adults. In infants and children, clinical features include skeletal, respiratory and neurologic complications, while recurrent, poorly healing fractures, muscle weakness and arthropathy are common in adults. Persistently low serum alkaline phosphatase is the cardinal biochemical feature of the disease. Management requires a dedicated multidisciplinary team. In mild cases, treatment is usually symptomatic. Severe cases, with life-threating or debilitating complications, can be successfully treated with enzyme replacement therapy with asfotase alfa.

Prevalence of low alkaline phosphatase activity in laboratory assessment: Is hypophosphatasia an underdiagnosed disease?

Background

Tissue-nonspecific alkaline phosphatase (TNSALP) encoded by the ALPL gene is of particular importance for bone mineralization. Mutation in the ALPL gene can lead to persistent low ALP activity resulting in the rare disease Hypophosphatasia (HPP) that is characterized by disturbed bone and dental mineralization. While severe forms are extremely rare with an estimated prevalence of 1/100.000, recent studies suggest that moderate form caused by heterozygous mutations are much more frequent with an estimated prevalence of 1/508. The purpose of this study was to estimate the prevalence of low AP levels in the population based on laboratory measurements.

Methods

In this study, the prevalence of low AP activity and elevated pyridoxal-5-phosphate (PLP) levels was analyzed in 6.918.126 measurements from 2011 to 2016 at a single laboratory in northern Germany. Only laboratory values of subjects older than 18 years of age were included. Only the first measurement was included, all repeated values were excluded.

Results

In total, 8.46% of the measurements of a total of 6.918.126 values showed a value < 30 U/L. 0.59% of the subjects with an ALP activity below 30 U/L had an additional PLP measurement. Here, 6.09% showed elevated pyridoxal-5-phosphate (PLP) levels. This suggest that 0.52% (1:194) of subjects show laboratory signs of HPP.

Conclusion

These data support the genetic estimation that the prevalence of moderate forms of HPP may be significantly higher than expected. Based on these data, we recommend automatically measurement of PLP in the case of low ALP activity and a notification to the ordering physician that HPP should be included in the differential diagnosis and further exploration is recommended.

Novel mutation in the ALPL gene with a dominant negative effect in a Japanese family

INTRODUCTION

Hypophosphatasia (HPP) is caused by mutations in the ALPL gene encoding tissue nonspecific alkaline phosphatase (TNSALP) and inherited in either an autosomal recessive or autosomal dominant manner. It is characterized clinically by defective mineralization of bone, dental problems, and low serum ALP levels. In the current report, we demonstrate a novel mutation in the ALPL gene (c.244G > A p.Gly82Arg) in a Japanese family with low serum ALP levels.

MATERIALS AND METHODS

The ALPL gene analysis using hybridization capture-based next-generation sequencing was performed. The expression plasmids of the wild type and mutated TNSALP were introduced into COS-7 cells. The enzymatic activity of ALP in the cell lysates was measured using p-nitrophenylphosphate as a substrate.

RESULTS

TNSALP with the novel ALPL mutation (c.244G > A p.Gly82Arg) completely lost its enzymatic activity and suppressed that of wild-type TNSALP, corroborating its dominant negative effect. The diagnosis of autosomal dominant HPP was confirmed in three members of the family.

CONCLUSION

Our approach would help to avoid the inappropriate use of bone resorption inhibitors for currently mis- or under-diagnosed HPP, given that the presence of further, yet undetected mutations of the ALPL gene are plausible.

Hypophosphatasia: is it an underdiagnosed disease even by expert physicians?

INTRODUCTION

Hypophosphatasia (HPP) is caused by mutations in the ALPL that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (ALP). Clinical manifestations range from extreme life-threatening lethal forms to no signs or symptoms at all.

MATERIALS AND METHODS

Consecutive 30,000 outpatients and inpatients with ALP data were screened retrospectively, out of which 1000 patients were found to have low levels of ALP more than once. Then, patients were evaluated for the symptoms and signs of HPP with further biochemical and genetic analyses.

RESULTS

Thirty-seven patients who had severe musculoskeletal pain, recurrent fractures, and tooth anomalies were then screened with substrate and DNA sequencing analyses for HPP. It was determined that eight patients had variants in the ALPL gene. A total of eight different ALPL variants were identified in eight patients. The variants, namely c.244G > C (p.Gly82Arg), c.1444C > T (p.His482Tyr), c.1487A > G (p.Asn493Ser), and c.675_676insCA (p.Met226GlnfsTer52), had not been previously reported.

DISCUSSION

Considering the wide spectrum of clinical signs and symptoms, HPP should be among the differential lists of bone, muscle, and tooth abnormalities at any age.

Biochemical, clinical and genetic characteristics in adults with persistent hypophosphatasaemia; Data from an endocrinological outpatient clinic in Denmark

Background

Hypophosphatasia (HPP) is an inborn disease caused by pathogenic variants in ALPL. Low levels of alkaline phosphatase (ALP) are a biochemical hallmark of the disease. Scarce knowledge about the prevalence of HPP in Scandinavia exists, and the variable clinical presentations make diagnostics challenging. The aim of this study was to investigate the prevalence of ALPL variants as well as the clinical and biochemical features among adults with endocrinological diagnoses and persistent hypophosphatasaemia.

Methods

A biochemical database containing ALP measurements of 26,121 individuals was reviewed to identify adults above 18 years of age with persistently low levels of ALP beneath range (≤ 35 ± 2.7 U/L). ALPL genetic testing, biochemical evaluations and assessment of clinical features by a systematic questionnaire among included patients, were performed.

Results

Among 24 participants, thirteen subjects (54.2%) revealed a disease-causing variant in ALPL and reported mild clinical features of HPP, of which musculoskeletal pain was the most frequently reported (n = 9). The variant c. 571G > A; p.(Glu191Lys) was identified in six subjects, and an unreported missense variant (c.1019A > C; p.(His340Pro)) as well as a deletion of exon 2 were detected by genetic screening. Biochemical analyses showed no significant differences in ALP (p = 0.059), the bone specific alkaline phosphatase (BALP) (p = 0.056) and pyridoxal-5′-phosphate (PLP) (p = 0.085) between patients with an ALPL variant and negative genetic screening. Patients with a variant in ALPL had significantly higher PLP levels than healthy controls (p = 0.002). We observed normal ALP activity in some patients classified as mild HPP, and slightly increased levels of PLP in two subjects with normal genetic screening and four healthy controls. Among 51 patients with persistent hypophosphatasaemia, fifteen subjects (29.4%) received antiresorptive treatment. Two patients with unrecognized HPP were treated with bisphosphonates and did not show complications due to the treatment.

Conclusions

Pathogenic variants in ALPL are common among patients with endocrinological diagnoses and low ALP. Regarding diagnostics, genetic testing is necessary to identify mild HPP due to fluctuating biochemical findings. Antiresorptive treatment is a frequent reason for hypophosphatasaemia and effects of these agents in adults with a variant in ALPL and osteoporosis remain unclear and require further studies.

•

Mild HPP is overlooked among adults with endocrinological diagnoses.

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Biochemical hallmarks of HPP can fluctuate to normal among mild forms.

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Genetic screening of ALPL including MLPA is necessary to identify mild HPP.

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Musculoskeletal pain is the most common symptom in adult HPP.

•

Effects of bisphosphonates in mild HPP need further studies.

A two-year follow-up of asfotase alfa replacement in a patient with hypophosphatasia: clinical, biochemical, and radiological evaluation

Hypophosphatasia (HPP) is a rare disease with a high mortality rate in its severe forms. It is caused by mutations within the gene encoding the tissue-nonspecific alkaline phosphatase (TNSALP), an enzyme responsible for bone mineralization. In 2015, the Food and Drug Administration approved the use of asfotase alfa, the first medication showing benefit in the treatment of HPP. We describe a case with a 2-year follow-up of the first Brazilian child treated with asfotase alfa. A 5-year-old boy, born to consanguineous parents, was diagnosed with HPP at the age of 20 months. During prenatal ultrasonography, polyhydramnios and shortening of long bones were detected. After birth, he presented delayed motor development, repeated respiratory infections, and bone deformities. At the age of 2 years and 8 months, he started walking and had already lost his primary teeth. He had reduced levels of alkaline phosphatase (ALP), elevated levels of pyridoxal 5'-phosphate (PLP), and a p.Ala33Val (c.98C>T) missense mutation in homozygosis in the TNSALP gene. His parents and sister also had reduced ALP levels, high PLP levels, and the same mutation in heterozygosis. His father and sister were healthy, and his mother was diagnosed with rickets in childhood, which resulted in short physical stature and lower limb deformities. The patient was started on asfotase alfa at the age of 2 years and 10 months. After 2 years of treatment, he improved his motor skills, had no further episodes of severe respiratory infection, and showed improved radiological findings of rickets, without any severe side effect.

Hypophosphatasia: A Unique Disorder of Bone Mineralization

Hypophosphatasia (HPP) is a rare genetic disease characterized by a decrease in the activity of tissue non-specific alkaline phosphatase (TNSALP). TNSALP is encoded by the ALPL gene, which is abundantly expressed in the skeleton, liver, kidney, and developing teeth. HPP exhibits high clinical variability largely due to the high allelic heterogeneity of the ALPL gene. HPP is characterized by multisystemic complications, although the most common clinical manifestations are those that occur in the skeleton, muscles, and teeth. These complications are mainly due to the accumulation of inorganic pyrophosphate (PPi) and pyridoxal-5′-phosphate (PLP). It has been observed that the prevalence of mild forms of the disease is more than 40 times the prevalence of severe forms. Patients with HPP present at least one mutation in the ALPL gene. However, it is known that there are other causes that lead to decreased alkaline phosphatase (ALP) levels without mutations in the ALPL gene. Although the phenotype can be correlated with the genotype in HPP, the prediction of the phenotype from the genotype cannot be made with complete certainty. The availability of a specific enzyme replacement therapy for HPP undoubtedly represents an advance in therapeutic strategy, especially in severe forms of the disease in pediatric patients.

Genotype-Phenotype Associations in 72 Adults with Suspected ALPL-Associated Hypophosphatasia

Hypophosphatasia (HPP) is a rare inborn error of metabolism due to a decreased activity of tissue nonspecific alkaline phosphatase (TNSALP). As the onset and severity of HPP are heterogenous, it can be challenging to determine the pathogenicity of detected rare ALPL variants in symptomatic patients. We aimed to characterize patients with rare ALPL variants to propose which patients can be diagnosed with adult HPP. We included 72 patients with (1) clinical symptoms of adult HPP or positive family history and (2) low TNSALP activity and/or high pyridoxal 5'-phosphate (PLP) levels, who underwent ALPL gene sequencing. The patients were analyzed and divided into three groups depending on ALPL variant pathogenicity according to the classification of the American College of Medical Genetics and Genomics (ACMG). Reported pathogenic (n = 34 patients), rare (n = 17) and common (n = 21) ALPL variants only were found. Muscular complaints were the most frequent symptoms (> 80%), followed by bone affection (> 50%). Tooth involvement was significantly more common in patients with pathogenic or rare ALPL variants. Seven rare variants could be classified as likely pathogenic (ACMG class 4) of which five have not yet been described. Inconclusive genetic findings and less specific symptoms make diagnosis difficult in cases where adult HPP is not obvious. As not every pathogenic or rare ALPL variant leads to a manifestation of HPP, only patients with bone complications and at least one additional complication concerning teeth, muscle, central nervous and mental system, repeated low TNSALP activity and high PLP levels should be diagnosed as adult HPP if rare ALPL gene variants of ACMG class 4 or higher support the diagnosis.

Clinical and biochemical characteristics of adults with hypophosphatasia attending a metabolic bone clinic

OBJECTIVES

This study sought to identify the clinical and biochemical characteristics that would help distinguish hypophosphatasia (HPP) from other metabolic bone diseases in adult patients attending a metabolic bone clinic by comparing patients who have genetically confirmed HPP with a group of patients with low bone mineral density (BMD) in the osteoporotic or osteopenic range.

METHODS

Data were collected from February 2016 to October 2018 for 41 patients (n = 20 in the HPP group, n = 21 in the low-BMD group) attending the metabolic bone clinic at Sheffield, United Kingdom (UK) or who were recruited via the Rare UK Diseases Study (RUDY) platform during the same period. A study questionnaire was administered to all patients, and assessments were conducted for laboratory values, physical functions, BMD, and spine imaging.

RESULTS

Patients with HPP were characterized as being younger, more likely to have metatarsal or femoral shaft fractures, and less likely to have vertebral fractures compared with patients in the low-BMD group. The HPP group had lower total and bone-specific alkaline phosphatase, higher pyridoxal 5'-phosphate (PLP), and lower, albeit sufficient, 25-hydroxyvitamin D. Low-BMD group had lower C-terminal telopeptide and tartrate-resistant acid phosphatase 5b (61.9% were on bisphosphonates at enrollment). Dual X-ray absorptiometry (DXA) analysis found that the HPP group had higher total hip and lumbar BMD T- and Z-scores compared with the low-BMD group. There were no differences found between the two groups with physical functional assessments. Results of receiver operating characteristic analysis indicated strong diagnostic accuracy of these biomarkers for HPP. Thresholds of total alkaline phosphatase (ALP) activity of 43 IU/L or less and PLP level of 120 nmol/L or more were determined to be potentially clinically useful for distinguishing HPP from other metabolic bone diseases.

CONCLUSION

This study supported the use of ALP and PLP measurements as predictive of HPP diagnosis along with certain demographic and clinical characteristics (younger age, metatarsal or femoral fractures without low mean BMD T- and Z-scores on a DXA scan) that can aid in recognizing adults who should be further evaluated for HPP. The critical values identified need to be applied to an independent sample to be tested for diagnostic accuracy.

Bone healing and reactivation of remodeling under asfotase alfa therapy in adult patients with pediatric-onset hypophosphatasia

Hypophosphatasia (HPP) is a hereditary musculoskeletal disorder caused by inactivating variants in the ALPL gene and subsequently reduced serum tissue-nonspecific alkaline phosphatase (TNSALP) activity. This inborn error of metabolism results in decreased bone quality, accumulations of osteoid, and reduced bone mineralization. Increased incidence of fractures and prolonged bone healing are characteristic features for HPP. Available enzyme replacement therapy (asfotase alfa), was reported to recover bone mineralization and bone quality in adult HPP patients. Moreover, it was shown that asfotase alfa improved fracture healing of former nonunions in two adult HPP patients. We hypothesized that the nonunions are filled partially with osteoid, offering great potential to benefit from the treatment with asfotase alfa to promote bone healing. In the present study, we report three adult patients with pediatric-onset HPP and detected ALPL-mutations with prolonged bone healing after arthrodesis, tibial stress fracture, and osteotomy. After the initiation of asfotase alfa, immediately increased levels of alkaline phosphatase (ALP) and bone-specific ALP, as well as decreased levels of pyridoxal-5-phosphate (PLP), were detected in biochemical analysis. Importantly, even after up to 5 years of non-healing, a progredient consolidation was shown, assessed by a custom three-dimensional evaluation of repeated cone-beam computed tomography (CBCT) images, characterized by rapidly increasing levels of bone volume per tissue volume (BV/TV) within the volume of interest (i.e., the region of the non-healing bone). These radiographical findings were in line with the reported restoration of functional ability and pain-free full weight-bearing, as well as increased neuromuscular parameters (e.g., improved muscle strength). Taken together, our findings indicate that asfotase alfa improves the osseous consolidation of nonunions likely due to re-mineralization of osteoid tissue filling the former gap and improving the functional ability in adult HPP patients, characterized by increasing levels of BV/TV assessed via an innovative three-dimensional evaluation of CBCT images.

Bone mineral density and fracture risk in adult patients with hypophosphatasia

In adult hypophosphatasia (HPP) patients, elevated lumbar spine dual X-ray absorptiometry (DXA) values are associated with markers of disease severity and disease-specific fracture risk while femoral bone mineral density (BMD), being largely unaffected by the disease severity, may still be useful to monitor other causes of increased fracture risk due to low BMD.

INTRODUCTION

Hypophosphatasia (HPP) is a rare inherited metabolic disorder due to deficient activity of the tissue-nonspecific alkaline phosphatase (TNAP). Clinical manifestation in adult HPP patients is manifold including an increased risk for fractures, but data regarding clinical significance of DXA measurement and associations with fracture risk and disease severity is scarce.

METHODS

Retrospective single-center analysis of DXA scans in patients with confirmed HPP (documented mutation, clinical symptoms, low alkaline phosphatase activity). Further data evaluation included disease-related fractures, laboratory results (alkaline phosphatase, pyridoxalphosphate, phosphoethanolamine), and medical history.

RESULTS

Analysis included 110 patients (84 female, mean age of 46.2 years) of whom 37.3% (n = 41) were harboring two mutations. Average T-Score level at the lumbar spine was - 0.1 (SD 1.9), and mean total hip T-Score was - 1.07 (SD 0.15). Both lower ALP activity and higher substrate levels (pyridoxalphosphate and phosphoethanolamine) were significantly correlated with increased lumbar spine T-Score levels (p < 0.001) while BMD at the hip was not affected by indicators of disease severity. Increased lumbar spine BMD was significantly associated with an increased risk for HPP-related fractures, prevalent in 22 (20%) patients (p < 0.001) with 21 of them having biallelic mutations.

CONCLUSION

BMD in adult HPP patients is not systematically reduced. Conversely, increased lumbar spine BMD appears to be associated with severely compromised mineralization and increased risk for HPP-related fractures while BMD at the hip appears unaffected by indicators of disease severity, suggesting suitability of this anatomic location for assessing and discerning disorders with increased fracture risk owing to reduced BMD like osteoporosis.

TRIAL REGISTRATION NUMBER

German register for clinical studies (DRKS00014022) DATE OF REGISTRATION: 02/10/2018 - retrospectively registered.

Tissue Nonspecific Alkaline Phosphatase Function in Bone and Muscle Progenitor Cells: Control of Mitochondrial Respiration and ATP Production

Tissue nonspecific alkaline phosphatase (TNAP/Alpl) is associated with cell stemness; however, the function of TNAP in mesenchymal progenitor cells remains largely unknown. In this study, we aimed to establish an essential role for TNAP in bone and muscle progenitor cells. We investigated the impact of TNAP deficiency on bone formation, mineralization, and differentiation of bone marrow stromal cells. We also pursued studies of proliferation, mitochondrial function and ATP levels in TNAP deficient bone and muscle progenitor cells. We find that TNAP deficiency decreases trabecular bone volume fraction and trabeculation in addition to decreased mineralization. We also find that Alpl^−/− mice (global TNAP knockout mice) exhibit muscle and motor coordination deficiencies similar to those found in individuals with hypophosphatasia (TNAP deficiency). Subsequent studies demonstrate diminished proliferation, with mitochondrial hyperfunction and increased ATP levels in TNAP deficient bone and muscle progenitor cells, plus intracellular expression of TNAP in TNAP+ cranial osteoprogenitors, bone marrow stromal cells, and skeletal muscle progenitor cells. Together, our results indicate that TNAP functions inside bone and muscle progenitor cells to influence mitochondrial respiration and ATP production. Future studies are required to establish mechanisms by which TNAP influences mitochondrial function and determine if modulation of TNAP can alter mitochondrial respiration in vivo.

Characterization of physical, functional, and cognitive performance in 15 adults with hypophosphatasia

OBJECTIVE

Given the small but growing body of literature related to physical functioning and the scarce data related to fine motor and cognitive functioning in adults with hypophosphatasia (HPP), our objective was to characterize physical, functional, and cognitive performance in adults with HPP. A future objective is to utilize this characterization to develop guidelines for evaluation by physical therapists (PT), occupational therapists (OT), and speech-language pathologists (SLP).

METHOD

We evaluated physical, functional, and cognitive performance in 15 adults with HPP through standardized assessments of mobility, balance, fine motor control, activities of daily living, cognition, and self-reported measures of health-related quality of life, fatigue, depression, and anxiety. The median age at enrollment was 44 years (range 26-79 years). Among the participants, 11 (73%) were women. Five participants (33%) were on enzyme replacement therapy.

RESULTS

Compared with the general population, HPP participants traveled shorter distances on the Six-Minute Walk Test (420 m (m) [SD: 132] vs 620 m [SD: 49], p < 0.00005), had slower gait on the 10-Meter Walk Test [HPP men (3.71 ft/s (f/s) [SD: 0.77] vs 4.70 f/s [SD: 0.14], p < 0.00005) and HPP women (3.39 f/s [SD: 0.67] vs 4.56 f/s [SD: 0.09], p < 0.00005)]. HPP participants had decreased upper extremity (UE) dexterity by Nine Hole Peg Test [right UE in HPP men (22.7 s (s) [SD: 2.3] vs 19.0 s [SD: 3.9], p = 0.03), left UE in HPP men (23.3 s [SD: 0.7] vs 19.8 s [SD: 3.7], p = 0.03), right UE in HPP women (19.8 s [SD: 2.0] vs 17.7 s [SD: 3.2], p = 0.01), and left UE in HPP women (21.1 s [SD: 2.5] vs 18.9 s[SD: 3.4], p = 0.02)], and some had abnormally slow bilateral UE reaction times via Dynavision (0.9 s [0.85,0.96], functional speed <1.15 s). On the Short Form-36 (SF36), HPP patients reported worse energy/fatigue (30.4 [SD 22.7] vs 52.2 [SD: 22.4], p = 0.0001), social functioning (54.5 [SD: 34.2] vs 78.8 [SD: 25.5], p = 0.0002), pain (46.1 [SD: 27.3] vs 70.8 [SD: 25.5], p = 0.0001), general health (36.8 [SD: 24.0] vs 57.0 [SD: 21.1], p = 0.0002), and health change i.e. perception of health improvement (32.1 [SD: 15.3] vs 59.1 [SD: 23.1], p < 0.00005) than the general population. Fatigue Severity Scale scores were well above the median for a healthy population (5.21 [SD: 1.8] vs 2.3 [SD: 1.21], p < 0.00005), indicating significant fatigue. HPP participants had significantly higher DASS scores for depression (8.5 [SD: 6.5] vs 5.0 [SD: 7.5], p = 0.02), anxiety (7.9 [SD: 6.7] vs 3.4 [SD: 5.1], p = 0.00009), and stress (14.7 [SD: 12.4] vs 8.1 [SD: 8.4], p = 0.0003) compared to the general population.

CONCLUSION

Objective functional assessments demonstrated defects in physical functioning, including decreased ability to walk distances, slow gait speed, and diminished ability to repeatedly rise from a sitting position. In addition, participants self-reported significant limitations due to physical dysfunction. Decreased upper extremity dexterity may indicate problems with activities of daily living and delayed reaction times can have safety implications. Some patients with HPP have increased difficulties with depression, anxiety, and stress. PT, OT, and SLP specialists can aid in establishing baseline assessment of impairment and objective metrics for assessing efficacy of treatment.

Intrafamilial phenotypic distinction of hypophosphatasia with identical tissue nonspecific alkaline phosphatase gene mutation: a family report

Hypophosphatasia (HPP) is caused by mutations in the tissue nonspecific alkaline phosphatase (TNSALP) gene in an autosomal recessive or dominant manner and characterized by defective mineralization of bone and low serum ALP levels. In this report, we present a family with HPP mother (case 1) and HPP child (case 2) who have identical TNSALP gene mutation (c.1015G>A p.Gly339Arg heterozygous mutation) but distinct clinical phenotypes. Whereas case 1 appeared to be asymptomatic despite extremely low levels of serum ALP, case 2 had several HPP-related symptoms, such as tooth loss, fractures, short stature, with slightly decreased ALP levels. Upon the diagnosis of HPP, case 1 discontinued denosumab, which was used to treat her rheumatoid arthritis, concerning the risk of atypical femoral fractures. The clinical course of this family was suggestive in a genotype-phenotype imbalance in HPP, the underdiagnosis of HPP in adults, and the risk of atypical femoral fractures using bone resorption inhibitors.

A novel de novo heterozygous ALPL nonsense mutation associated with adult hypophosphatasia

Using genetic, clinical, biochemical, and radiographic assessment and bioinformatic approaches, we present an unusual case of adult HPP caused by a novel de novo heterozygous nonsense mutation in the alkaline phosphatase (ALPL).

INTRODUCTION

Hypophosphatasia (HPP) is caused by genetic alterations of the ALPL gene, encoding the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). Here, the purpose was to perform clinical and molecular investigation in a 36-year-old Caucasian woman suspected to present adult HPP.

METHODS

Medical and dental histories were obtained for the proposita and family members, including biochemical, radiographic, and dental assessments. ALPL mutational analysis was performed by the Sanger sequencing method, and the functional impact prediction of the identified mutations was assessed by bioinformatic methods.

RESULTS

We identified a novel heterozygous nonsense mutation in the ALPL gene (NM_000478.6:c.768G>A; W[TGG]>*[TGA]) associated with spontaneous vertebral fracture, severe back pain, musculoskeletal pain, low bone density, and short-rooted permanent teeth loss. Functional prediction analysis revealed that the Trp256Ter mutation led to a complete loss of TNSALP crown domain and extensive loss of other functional domains (calcium-binding domain, active site vicinity, and zinc-binding site) and over 60% loss of homodimer interface residues, suggesting that the mutant TNSALP molecules are nonfunctional and form unstable homodimers. Genotyping of the ALPL in the proposita's parents, sister, and niece revealed that in this case, HPP occurred due to a de novo mutation.

CONCLUSION

The present study describes a novel genotype-phenotype and structure-function relationship for HPP, contributing to a better molecular comprehension of HPP etiology and pathophysiology.

Burden of Illness in Adults With Hypophosphatasia: Data From the Global Hypophosphatasia Patient Registry

Hypophosphatasia (HPP) is a rare, inherited, metabolic disease caused by deficient tissue non-specific alkaline phosphatase activity. This study aims to assess patient-reported pain, disability and health-related quality of life (HRQoL) in a real-world cohort of adults with HPP who were not receiving asfotase alfa during the analysis. Adults (≥18 years old) with HPP (confirmed by ALPL gene mutation and/or low serum alkaline phosphatase activity for age/sex) were identified from the Global HPP Registry (NCT02306720). Demographics, clinical characteristics, and data on patient-reported pain, disability, and HRQoL (assessed by Brief Pain Inventory Short Form [BPI-SF], Health Assessment Questionnaire Disability Index [HAQ-DI], and 36-Item Short-Form Health Survey version 2 [SF-36v2], respectively) were stratified by pediatric- and adult-onset HPP and summarized descriptively. Of the 304 adults included (median [min, max] age 48.6 [18.8, 79.8] years; 74% women), 45% had adult-onset HPP and 33% had pediatric-onset HPP (unknown age of onset, 22%). Of those with data, 38% had experienced ≥5 HPP manifestations and 62% had a history of ≥1 fracture/pseudofracture. Median (Q1, Q3) BPI-SF scores were 3.5 (1.5, 5.3) for pain severity and 3.3 (0.9, 6.2) for pain interference. Median (Q1, Q3) disability on the HAQ-DI was 0.3 (0.0, 0.7). Median (Q1, Q3) physical and mental component summary scores on the SF-36v2 were 42.4 (32.7, 49.9) and 45.3 (36.3, 54.8), respectively. Greater numbers of HPP manifestations experienced/body systems affected correlated significantly with poorer scores on the BPI-SF, HAQ-DI, and SF-36v2 (all p < 0.05). No significant differences between adults with pediatric- and adult-onset HPP were observed for patient-reported outcomes, except for disability and the BPI-SF question "pain at its worst," which were significantly higher among adults with pediatric- versus adult-onset HPP (p = 0.03 and 0.04, respectively). These data from the Global HPP Registry show that adults with HPP have a substantial burden of illness that is associated with reduced patient-reported HRQoL, regardless of age of disease onset. © 2020 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

Spectrum of microarchitectural bone disease in inborn errors of metabolism: a cross-sectional, observational study

BACKGROUND

Patients diagnosed with inborn errors of metabolism (IBEM) often present with compromised bone health leading to low bone density, bone pain, fractures, and short stature. Dual-energy X-ray absorptiometry (DXA) is the current gold standard for clinical assessment of bone in the general population and has been adopted for monitoring bone density in IBEM patients. However, IBEM patients are at greater risk for scoliosis, short stature and often have orthopedic hardware at standard DXA scan sites, limiting its use in these patients. Furthermore, DXA is limited to measuring areal bone mineral density (BMD), and does not provide information on microarchitecture.

METHODS

In this study, microarchitecture was investigated in IBEM patients (n = 101) using a new three-dimensional imaging technology high-resolution peripheral quantitative computed tomography (HR-pQCT) which scans at the distal radius and distal tibia. Volumetric BMD and bone microarchitecture were computed and compared amongst the different IBEMs. For IBEM patients over 16 years-old (n = 67), HR-pQCT reference data was available and Z-scores were calculated.

RESULTS

Cortical bone density was significantly lower in IBEMs associated with decreased bone mass when compared to lysosomal storage disorders (LSD) with no primary skeletal pathology at both the radius and tibia. Cortical thickness was also significantly lower in these disorders when compared to LSD with no primary skeletal pathology at the radius. Cortical porosity was significantly greater in hypophosphatasia when compared to all other IBEM subtypes.

CONCLUSION

We demonstrated compromised bone microarchitecture in IBEMs where there is primary involvement of the skeleton, as well as IBEMs where skeletal complications are a secondary outcome. In conclusion, our findings suggest HR-pQCT may serve as a valuable tool to monitor skeletal disease in the IBEM population, and provides insight to the greatly varying bone phenotype for this cohort that can be used for clinical monitoring and the assessment of response to therapeutic interventions.

Hypophosphatasia in adolescents and adults: overview of diagnosis and treatment

This article provides an overview of the current knowledge on hypophosphatasia-a rare genetic disease of very variable presentation and severity-with a special focus on adolescents and adults. It summarizes the available information on the many known mutations of tissue-nonspecific alkaline phosphatase (TNSALP), the epidemiology and clinical presentation of the disease in adolescents and adults, and the essential diagnostic clues. The last section reviews the therapeutic approaches, including recent reports on enzyme replacement therapy (EnzRT).

Dual X-ray absorptiometry has limited utility in detecting bone pathology in children with hypophosphatasia: A pooled post hoc analysis of asfotase alfa clinical trial data

Asfotase alfa is an enzyme replacement therapy approved for treatment of patients with pediatric-onset hypophosphatasia (HPP), a rare, inherited, systemic disease causing impaired skeletal mineralization, short stature, and reduced physical function in children. The role of dual X-ray absorptiometry (DXA) in the assessment of children with HPP has been insufficiently explored. This post hoc analysis included pooled DXA data from 2 open-label, multicenter studies in 19 children with HPP. The study population was aged ≥5 to <18 years and had received asfotase alfa for ≤6.6 years at enrollment (male: 79%; median age at enrollment: 10.4 y [range: 5.9-16.7]; treatment duration: 6.3 y [range: 0.1-6.6]. Baseline height Z-scores indicated short stature (median [min, max]: -1.26 [-6.6, 0]); mean [SD]: -2.30 [1.97]), thus requiring height adjustment of DXA Z-scores. At Baseline, few patients had height-adjusted bone mineral density (BMD_ht) Z-scores of -2 or less for whole body (n = 3) or lumbar spine (n = 5). In treated patients, mean whole body and lumbar spine BMD_htZ-scores did not change over time, but whole body and lumbar spine height- adjusted bone mineral content (BMC_ht) Z-scores increased significantly from Baseline to Last Assessment (P ≤ 0.0056). Improvements in Radiographic Global Impression of Change (RGI-C) scale scores correlated significantly with increases in whole body and lumbar spine BMC_htZ-scores (P < 0.05) but not BMD_htZ-Scores. Improvements in Rickets Severity Score (RSS) correlated significantly with increases in lumbar spine BMD_htZ-scores and whole body BMC_ht Z-scores (P < 0.05). No significant correlations were observed between any DXA and bone histomorphometry measure. These findings suggest that DXA BMD Z-scores, which are commonly used in clinical practice, have limited utility in assessing deficient bone mineralization in patients with HPP. Although BMC_htZ-scores increased significantly over time with asfotase alfa therapy, the lack of significant changes in more than one DXA parameter suggests that this tool may not be useful in everyday clinical practice. Furthermore, the use of BMC as an independent metric is not typical or recommended by guidelines. Complementary measures, such as skeletal radiographs supplemented with age-appropriate functional assessments, should be considered.

Mineral Intake and Clinical Symptoms in Adult Patients with Hypophosphatasia

BACKGROUND

Hypophosphatasia (HPP) is a rare inherited metabolic disorder characterized by deficient activity of the tissue-nonspecific alkaline phosphatase entailing impaired turnover of phosphorus metabolites. Dietary mineral intake is suspected to influence clinical symptoms of HPP, but scientific evidence is missing.

METHODS

Cross-sectional matched-pairs study collecting comprehensive data on nutrient intake in 20 HPP patients and 20 unaffected, age- and gender-matched controls. Dietary information and clinical symptoms were documented in detail over 7 consecutive days using structured diaries.

RESULTS

Baseline data and type of energy-supplying nutrients were balanced between both groups. Median nutritional intake of phosphorus and calcium were significantly lower in HPP patients versus controls, which is partially attributable to lower energy consumption in HPP patients. Differences regarding phosphorus and calcium (Ca/P) ratio and uptake of magnesium, zinc, and vitamin B6 were not statistically significant. Both high (≥ 1375 mg/d) and low intakes (< 1100 mg/d) of phosphorus were significantly associated with an increased frequency of neuropsychiatric symptoms (P = 0.02). Similarly, very high and very low intake of calcium was significantly associated with musculoskeletal (P < 0.01), gastrointestinal (P = 0.02), and neuropsychiatric (P < 0.001) symptoms. An increased Ca/P ratio was associated with increased tiredness/fatigue (P < 0.01), whereas a decreased Ca/P was associated with gastrointestinal issues (P = 0.01).

CONCLUSION

Phosphorus and calcium intake seem reduced in HPP patients along with reduced total energy consumption. Particularly high as well as very low absolute or unbalanced phosphorus and calcium intake are associated with an increased frequency of clinical symptoms.

Hypophosphatasia in Adults: Clinical Spectrum and Its Association With Genetics and Metabolic Substrates

BACKGROUND

Hypophosphatasia (HPP) is a rare metabolic bone disorder caused by mutations in the alkaline phosphatase (ALPL) gene, and characterized by low circulating alkaline phosphatase (ALP) levels and bone, muscle, dental and systemic manifestations. In this case series we investigate the clinical spectrum, genetic and biochemical profile of adult HPP patients from the University Hospitals Leuven, Belgium.

METHODOLOGY

Adults with HPP were identified through medical record review. Inclusion criteria were: (1) age ≥ 16 yr; (2) consecutively low ALP levels not explained by secondary causes; (3) one or more of the following supporting criteria: biochemical evidence of elevated enzyme substrates; subtrochanteric fractures, metatarsal fractures or other typical clinical features; family history of HPP; a known or likely pathogenic ALPL mutation.

RESULTS

Nineteen patients met our inclusion criteria (n = 2 infantile, n = 6 childhood, n = 10 adult-onset HPP and one asymptomatic carrier). Fractures and dental abnormalities were the most reported symptoms. Fatigue was reported in n = 7/19 patients (37%), three of which had previously been misdiagnosed as having chronic fatigue syndrome and/or fibromyalgia. Empirical pyridoxine therapy in four patients (without seizures) did not provide symptomatic relief. N = 7/19 patients (37%) were inappropriately treated or planned to be treated with antiresorptive treatment. Two patients developed atypical femoral fractures following exposure to bisphosphonates and/or denosumab. Patients detected by screening were less severely affected, while patients with homozygous or compound heterozygous mutations had the most severe symptoms, significantly lower circulating ALP levels (p = 0.013) and significantly higher pyridoxal-5'-phosphate (p = 0.0018) and urinary phosphoethanolamine (p = 0.0001) concentrations.

CONCLUSIONS

Screening may detect mainly less severely affected individuals, which may nevertheless avoid misdiagnosis and inappropriate antiresorptive drug exposure. Patients with biallelic mutations had more severe symptoms, significantly lower ALP and higher substrate levels. Whether the latter finding has implications for the classification and treatment of HPP should be investigated further in larger cohorts.

Enzyme therapy: a forerunner in catalyzing a healthy society?

INTRODUCTION

The use of enzymes in various industries has been prevalent for centuries. However, their potency as therapeutics remained latent until the late 1950 s, when scientists finally realized the gold mine they were sitting on. Enzyme therapy has seen rapid development over the past few decades and has been widely used for the therapy of myriad diseases, including lysosomal storage disorders, cancer, Alzheimer's disease, irritable bowel syndrome, exocrine pancreatic insufficiency, and hyperuricemia. Enzymes are also used for wound healing, the treatment of microbial infections, and gene therapy.

AREAS COVERED

This is a comprehensive review of the therapeutic use of enzymes that can act as a guidepost for researchers and academicians and presents a general overview of the developments in enzyme therapy over the years, along with updates on recent advancements in enzyme therapy research.

EXPERT OPINION

Although enzyme therapy is immensely beneficial and induces little auxiliary damage, it has several drawbacks, ranging from high cost, low stability, low production, and hyperimmune responses to the failure to cure a variety of the problems associated with a disease. Further fine-tuning and additional clinical efficacy studies are required to establish enzyme therapy as a forerunner to catalyzing a healthy society.

Effect of Asfotase Alfa on Muscle Weakness in a Japanese Adult Patient of Hypophosphatasia with Low ALP Levels

A 40-year-old Japanese woman presented to our hospital with general fatigue and muscle weakness. She had a history of premature loss of deciduous teeth at 4 years old, her serum alkaline phosphatase (ALP) activity was as low as 91 U/L, and radiologic studies revealed thoracic deformity and sacroiliac calcification. Genetic sequencing revealed a heterozygous c.1559delT mutation in the tissue non-specific alkaline phosphatase gene (ALPL). Based on these findings, she was diagnosed with hypophosphatasia (HPP), and treatment with asfotase alfa, a recombinant human tissue-nonspecific alkaline phosphatase (TNSALP), was initiated. After six months of treatment with asfotase alfa, improvements were observed in the SF-36 score, six-minute walk distance, and grasping power. Although the overdiagnosis needs to be avoided, HPP should be considered in patients with undiagnosed musculoskeletal symptoms and a low serum ALP activity.

Treatment of hypophosphatasia

Hypophosphatasia (HPP) is a rare disorder with perinatal, infantile, childhood, and adult presentations. Severe forms are autosomal recessive with an early onset, whereas milder forms have a later onset. The underlying cause of the disease is a mutation based on a genetic disorder of the tissue non-specific alkaline phosphatase (TNSALP) gene, leading on the one hand to decreased activity of the TNSALP enzyme, and on the other hand to accumulation of TNSALP substrates. Symptoms like non-traumatic and non-healing fractures, musculoskeletal pain, chondrocalcinosis, seizures, premature loss of fully rooted teeth or delayed development of milk teeth, respiratory insufficiency, and calcinosis in muscles, kidneys, and joints occur. Supportive treatment is important for HPP patients, including mechanical ventilation, accurate fracture treatment, physical therapy, dental monitoring, and follow-up care to avoid subsequent problems. A causal enzyme therapy replacement with asfotase-alfa was approved by the Food and Drug Administration (FDA) in 2015. Asfotase-alfa improves respiratory insufficiency, bone mineralization, and long-term survival, and has a very good safety profile.

Can we identify individuals with an ALPL variant in adults with persistent hypophosphatasaemia?

Background

Hypophosphatasia (HPP) is an inborn error of metabolism characterized by low levels of serum alkaline phosphatase (ALP). Scarce evidence exists about features that should signal the potential association between hypophosphatasaemia and HPP in adults. The aim of this study is to estimate the prevalence of ALPL variants in subjects with persistent hypophosphatasaemia and determine the associated clinical and laboratory features. For this cross-sectional study, laboratory records of 386,353 subjects were screened by measurement of ALP activity. A total of 85 (0.18%) subjects with persistent hypophosphatasaemia (≥2 serum alkaline phosphatase–ALP–measurements ≤35 IU/L and none > 45 IU/L) were included (secondary causes previously discarded). ALPL genetic testing and a systematized questionnaire to retrieve demographic, clinical and laboratory data were performed. Descriptive analysis and logistic regression models were employed to identify the clinical and laboratory characteristics associated with ALPL variants.

Results

Forty subjects (47%) had a variant(s) in ALPL. With regard to clinical characteristics, the presence of an ALPL variant was significantly associated only with musculoskeletal pain (OR: 7.6; 95% IC: 1.9–30.9). Nevertheless, a trend to present more dental abnormalities (OR: 3.6; 95% IC: 0.9–13.4) was observed. Metatarsal stress fractures were also more frequent (4 vs 0; p < 0.05) in this group. Regarding laboratory features, median ALP levels were lower in subjects with ALPL variants (26 vs 29 IU/L; p < 0.005). Interestingly, the threshold of ALP levels < 25 IU/L showed a specificity, positive predictive value and positive likelihood ratio of 97.8, 94.4% and 19.8 to detect a positive ALPL test, respectively.

Conclusions

In subjects with persistent hypophosphatasaemia –secondary causes excluded– one out of two presented ALPL variants. Musculoskeletal pain and ALP levels < 25 IU/L are associated with this variant(s). In this scenario, ALP levels < 25 IU/L seem to be very useful to identify individuals with the presence of an ALPL variant.

Adult hypophosphatasia with a novel ALPL mutation: Report of an Indian kindred

Hypophosphatasia is an inborn error in metabolism characterized by low serum alkaline phosphatase (ALP) activity resulting from deactivating mutations in TNSALP (also known as ALPL), the gene that encodes the ‘tissue-specific’ isoenzyme of ALP. The disease exhibits significant clinical heterogeneity that spans from death in utero to only dental complications in adult life. Herein, we report a 47-year-old woman presenting with fracture of shaft of left femur. She had been complaining of pain in both of her thighs for the past 3 years. In addition, she gave a history of premature loss of teeth. Review of old radiographs revealed pseudo-fractures involving the lateral cortices of the femora on both sides. Biochemical panel revealed hyperphosphatemia, persistently low total alkaline phosphatase (ALP) and low-normal bone turnover markers. Screening of her siblings revealed low ALP in her younger sister and brother who were otherwise free from any major dento-arthro-osseous complaints. Sanger sequencing showed a novel, heterozygous, missense mutation in exon 5 at position 311 (c.311a > g;p.104 Asn > Ser) of ALPL gene in the three members. The patient underwent open reduction and intramedullary nailing of left femur along with prophylactic nailing on right side. This case report represents the first genetically confirmed kindred of adult hypophosphatasia from the Indian subcontinent.