Hypophosphatasia. Review of 24 cases

Physiology and Clinical Manifestations of Pathologic Cranial Suture Widening

Cranial sutures are complex structures integrating mechanical forces with osteogenesis which are often affected in craniofacial syndromes. While premature fusion is frequently described, rare pathological widening of cranial sutures is a comparatively understudied phenomenon. This narrative review aims to bring to light the biologically variable underlying causes of widened sutures and persistent fontanelles leading to a common outcome. The authors herein present four syndromes, selected from a literature review, and their identified biological mechanisms in the context of altered suture physiology, exploring the roles of progenitor cell differentiation, extracellular matrix production, mineralization, and bone resorption. This article illustrates the gaps in understanding of complex craniofacial disorders, and the potential for further unification of genetics, cellular biology, and clinical pillars of health science research to improve treatment outcomes for patients.

Disorders of phosphate homeostasis in children, part 1: primer on mineral ion homeostasis and the roles of phosphate in skeletal biology

Phosphate has extensive physiological roles including energy metabolism, genetic function, signal transduction and membrane integrity. Regarding the skeleton, not only do phosphate and calcium form the mineral component of the skeleton, but phosphate is also essential in regulating function of skeletal cells. Although our understanding of phosphate homeostasis has lagged behind and remains less than that for calcium, considerable advances have been made since the recognition of fibroblast growth factor-23 (FGF23) as a bone-derived phosphaturic hormone that is a major regulator of phosphate homeostasis. In this two-part review of disorders of phosphate homeostasis in children, part 1 covers the basics of mineral ion homeostasis and the roles of phosphate in skeletal biology. Part 1 includes phosphate-related disorders of mineralization for which overall circulating mineral ion homeostasis remains normal. Part 2 covers hypophosphatemic and hyperphosphatemic disorders, emphasizing, but not limited to, those related to increased and decreased FGF23 signaling, respectively.

A primer on skeletal dysplasias

Skeletal dysplasia encompasses a heterogeneous group of over 400 genetic disorders. They are individually rare, but collectively rather common with an approximate incidence of 1/5000. Thus, radiologists occasionally encounter skeletal dysplasias in their daily practices, and the topic is commonly brought up in radiology board examinations across the world. However, many radiologists and trainees struggle with this issue because of the lack of proper resources. The radiological diagnosis of skeletal dysplasias primarily rests on pattern recognition-a method that is often called the "Aunt Minnie" approach. Most skeletal dysplasias have an identifiable pattern of skeletal changes composed of unique findings and even pathognomonic findings. Thus, skeletal dysplasias are the best example to which the Aunt Minnie approach is readily applicable.

Mimic for Child Physical Abuse: Biochemical and Genetic Evidence of Hypophosphatasia without Classic Radiologic Findings

Infants presenting with multiple fractures without a plausible accident history need to be evaluated for child abuse or underlying predisposing conditions such as osteogenesis imperfecta and hypophosphatasia. We present a case of infantile hypophosphatasia with multiple unexplained fractures but otherwise normal radiographs in the setting of biochemical and genetic evidence of hypophosphatasia. Standard screening tests for hypophosphatasia include serum alkaline phosphatase level and genetic testing. Despite the presented case's positive biochemical and genetic testing, the case did not have any other radiologic finding suggesting infantile hypophosphatasia, such as severe bone mineralization deficits and rickets. While patients with hypophosphatasia can have increased bone fragility, this has been reported in the context of radiologic abnormalities of the skeleton. Thus, this case is potentially the first reported infantile hypophosphatasia case presenting with no findings of rickets on radiographs, raising concern that the fractures and especially the radius head dislocation might be due to physical abuse.

Large-scale in vitro functional testing and novel variant scoring via protein modeling provide insights into alkaline phosphatase activity in hypophosphatasia

Hypophosphatasia (HPP) is a rare metabolic disorder characterized by low tissue‐nonspecific alkaline phosphatase (TNSALP) typically caused by ALPL gene mutations. HPP is heterogeneous, with clinical presentation correlating with residual TNSALP activity and/or dominant‐negative effects (DNE). We measured residual activity and DNE for 155 ALPL variants by transient transfection and TNSALP enzymatic activity measurement. Ninety variants showed low residual activity and 24 showed DNE. These results encompass all missense variants with carrier frequencies above 1/25,000 from the Genome Aggregation Database. We used resulting data as a reference to develop a new computational algorithm that scores ALPL missense variants and predicts high/low TNSALP enzymatic activity. Our approach measures the effects of amino acid changes on TNSALP dimer stability with a physics‐based implicit solvent energy model. We predict mutation deleteriousness with high specificity, achieving a true‐positive rate of 0.63 with false‐positive rate of 0, with an area under receiver operating curve (AUC) of 0.9, better than all in silico predictors tested. Combining this algorithm with other in silico approaches can further increase performance, reaching an AUC of 0.94. This study expands our understanding of HPP heterogeneity and genotype/phenotype relationships with the aim of improving clinical ALPL variant interpretation.

Efficacy and Safety of Asfotase Alfa in Infants and Young Children With Hypophosphatasia: A Phase 2 Open-Label Study

CONTEXT

Long-term data on enzyme replacement treatment of hypophosphatasia (HPP) are limited.

OBJECTIVE

To evaluate efficacy and safety of asfotase alfa in patients aged ≤5 years with HPP followed for up to 6 years.

DESIGN

Phase 2 open-label study (July 2010 to September 2016).

SETTING

Twenty-two sites; 12 countries.

PARTICIPANTS

Sixty-nine patients [median (range) age: 16.0 (0.02 to 72) months] with severe HPP and sign/symptom onset before age 6 months.

INTERVENTION

Asfotase alfa 2 mg/kg three times/week or 1 mg/kg six times/week subcutaneously.

MAIN OUTCOME MEASURES

Primary efficacy measure: Radiographic Global Impression of Change (RGI-C) score [-3 (severe worsening) to +3 (complete/near-complete healing)]. Additional outcome measures: respiratory status, growth, and safety. Post hoc analysis: characteristics of radiographic responders vs nonresponders at Year 1 (RGI-C: ≥+2 vs <+2).

RESULTS

During median (minimum, maximum) 2.3 (0.02, 5.8) years of treatment, RGI-C scores improved significantly at Month 6 [+2.0 (-1.7, +3.0)], Year 1 [+2.0 (-2.3, +3.0)], and Last Assessment [+2.3 (-2.7, +3.0); P < 0.0001 all]. Of 24 patients requiring respiratory support at Baseline, 11 (46%) no longer needed support. Height/weight z scores generally increased. Nine patients died (13%). All patients experienced at least one adverse event; pyrexia was most common. Compared with responders [n = 50 (72%)], nonresponders [n = 19 (28%)] had more severe disease at Baseline and a higher rate of neutralizing antibodies (NAbs) at Last Assessment.

CONCLUSIONS

Most infants/young children given asfotase alfa showed early radiographic and clinical improvement sustained up to 6 years; radiographic nonresponders had more severe disease and more frequent NAbs at Last Assessment.

Reliability and Validity of the 6-Minute Walk Test in Hypophosphatasia

This investigation evaluated the reliability and validity of the 6‐Minute Walk Test (6MWT) in patients with pediatric hypophosphatasia (HPP). Children (aged 6 to 12 years; n = 11), adolescents (13 to 17 years; n = 4), and adults (18 to 65 years; n = 9) completed the 6MWT at screening and baseline in two clinical studies of asfotase alfa. Test‐retest reliability of the 6MWT, evaluated with Pearson's correlation coefficients (r) for screening versus baseline, was high for children (r = 0.95; p < 0.0001), adolescents (r = 0.81; p = 0.125), and adults (r = 0.94; p = 0.0001). The most conservative minimal clinically important differences, estimated using distribution‐based methods, were 31 m (children and adults) and 43 m (adolescents). In children, the 6MWT correlated significantly with scores on measures of skeletal disease, which included the Radiographic Global Impression of Change scale (r = 0.50; p < 0.0001) and the Rickets Severity Scale (r = −0.78; p < 0.0001), such that distance walked increased as the severity of skeletal disease decreased. Significant (p < 0.0001) correlations with the 6MWT distance walked were also observed for children with scores on parent‐reported measures of disability (r = −0.67), ability to function in activities of daily living (r = 0.71 to 0.77), and parent‐reported measures of pain (r = −0.39). In adolescents and adults, 6MWT distance walked correlated significantly (p < 0.05) with measures of lower extremity function (r = 0.83 and 0.60, respectively), total pain severity (r = −0.41 and −0.36, respectively), and total pain interference (r = −0.41 and −0.49, respectively). Collectively, these data indicate that the 6MWT is a reliable, valid measure of physical functioning in patients with pediatric HPP. © 2018 The Authors. JBMR Plus Published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Asfotase alfa for infants and young children with hypophosphatasia: 7 year outcomes of a single-arm, open-label, phase 2 extension trial

BACKGROUND

Our previous phase 2, open-label study of 11 infants and young children with life-threatening perinatal or infantile hypophosphatasia showed 1 year safety and efficacy of asfotase alfa, an enzyme replacement therapy. We aimed to report the long-term outcomes over approximately 7 years of treatment.

METHODS

We did a prespecified, end of study, 7 year follow-up of our single-arm, open-label, phase 2 trial in which children aged 3 years or younger with life-threatening perinatal or infantile hypophosphatasia were recruited from ten hospitals (six in the USA, two in the UK, one in Canada, and one in the United Arab Emirates). Patients received asfotase alfa (1 mg/kg three times per week subcutaneously, adjusted to 3 mg/kg three times per week if required) for up to 7 years (primary treatment period plus extension phase) or until the product became commercially available; dosage adjustments were made at each visit according to changes in the patient's weight. The primary objectives of this extension study were to assess the long-term tolerability of asfotase alfa, defined as the number of patients with one or more treatment-emergent adverse events, and skeletal manifestations associated with hypophosphatasia, evaluated using the Radiographic Global Impression of Change (RGI-C) scale (-3 indicating severe worsening, and +3 complete or near-complete healing). Respiratory support, growth, and cognitive and motor functions were also evaluated. All efficacy and safety analyses were done in all patients who received any asfotase alfa (full-analysis population). This study and extension phase are registered with ClinicalTrials.gov, number NCT01205152, and EudraCT, number 2009-009369-32.

FINDINGS

11 participants were recruited between Oct 6, 2008, and Dec 4, 2009. Ten patients completed a 6 month treatment period and entered the extension phase; nine received asfotase alfa for at least 6 years and completed the study, with four being treated for more than 7 years. Skeletal healing was sustained over 7 years of treatment; all evaluable patients had RGI-C scores of at least +2 at year 6 (n=9; median score +2·0 [range 2·0-3·0]) and year 7 (n=7; median score +2·3 [2·0-3·0]). No patient who completed the study required respiratory support after year 4. Weight Z scores improved to within normal range from year 3 to study end; length or height Z scores improved but remained below normal. Age-equivalent scores on gross motor, fine motor, and cognitive subscales of the Bayley Scales of Infant and Toddler Development also improved. All 11 patients had at least one treatment-emergent adverse event. The most common adverse events were pyrexia (eight [73%] of 11 patients), upper respiratory tract infection (eight [73%]), craniosynostosis (seven [64%]), and pneumonia (seven [64%]). Serious adverse events related to asfotase alfa occurred in three (27%) patients (severe chronic hepatitis; moderate immediate post-injection reaction; and severe craniosynostosis with severe conductive deafness).

INTERPRETATION

Patients with perinatal or infantile hypophosphatasia treated with asfotase alfa for up to 7 years showed early, sustained improvements in skeletal mineralisation. Respiratory function, growth, and cognitive and motor function also improved, and asfotase alfa was generally well tolerated.

FUNDING

Alexion Pharmaceuticals, Inc.

Differential diagnosis of perinatal hypophosphatasia: radiologic perspectives

Perinatal hypophosphatasia (HPP) is a rare, potentially life-threatening, inherited, systemic metabolic bone disease that can be difficult to recognize in utero and postnatally. Diagnosis is challenging because of the large number of skeletal dysplasias with overlapping clinical features. This review focuses on the role of fetal and neonatal imaging modalities in the differential diagnosis of perinatal HPP from other skeletal dysplasias (e.g., osteogenesis imperfecta, campomelic dysplasia, achondrogenesis subtypes, hypochondrogenesis, cleidocranial dysplasia). Perinatal HPP is associated with a broad spectrum of imaging findings that are characteristic of but do not occur in all cases of HPP and are not unique to HPP, such as shortening, bowing and angulation of the long bones, and slender, poorly ossified ribs and metaphyseal lucencies. Conversely, absent ossification of whole bones is characteristic of severe lethal HPP and is associated with very few other conditions. Certain features may help distinguish HPP from other skeletal dysplasias, such as sites of angulation of long bones, patterns of hypomineralization, and metaphyseal characteristics. In utero recognition of HPP allows for the assembly and preparation of a multidisciplinary care team before delivery and provides additional time to devise treatment strategies.

Healthcare resource utilization in the management of hypophosphatasia in three patients displaying a spectrum of manifestations

Background

Hypophosphatasia (HPP) is a rare, heterogeneous disease caused by low tissue-nonspecific alkaline phosphatase activity and associated with a range of signs and symptoms, including bone mineralization defects, respiratory problems, seizures, premature tooth loss, and fractures. Data from patients with HPP and their healthcare resource utilization are lacking. We evaluated healthcare utilization for 3 patients with differing severities of HPP.

Results

Patient 1 had perinatal HPP (received enzyme replacement therapy asfotase alfa under a compassionate use program), Patient 2 had infantile HPP, and Patient 3 had childhood HPP. Healthcare resources used in the National Health Service, England, were identified from coded activities in the hospital database and detailed medical records. These data showed that healthcare utilization was directly related to disease severity. Patient 1 had respiratory complications necessitating prolonged admission for ventilation from birth. Over 2.5 years, this patient was hospitalized 725 days, with visits from 16 specialists. Patient 2 had HPP-associated signs and symptoms starting in infancy, was treated for craniosynostosis, experienced multiple fractures, and required outpatient management for > 18 years. Patient 3 developed signs and symptoms of HPP in childhood and received outpatient and day case treatment for dental, orthopedic, and cardiovascular problems over 24 years. Healthcare utilization varied with severity and complexity of disease manifestations between these patients.

Conclusions

With the recent approval of asfotase alfa for HPP, data from this analysis may help mobilize multidisciplinary healthcare resources for management of HPP by elucidating healthcare resource needs of patients who show a spectrum of clinical manifestations of HPP.

Monitoring guidance for patients with hypophosphatasia treated with asfotase alfa

Hypophosphatasia (HPP) is a rare, inherited, systemic, metabolic disorder caused by autosomal recessive mutations or a single dominant-negative mutation in the gene encoding tissue-nonspecific alkaline phosphatase (TNSALP). The disease is associated with a broad range of signs, symptoms, and complications, including impaired skeletal mineralization, altered calcium and phosphate metabolism, recurrent fractures, pain, respiratory problems, impaired growth and mobility, premature tooth loss, developmental delay, and seizures. Asfotase alfa is a human, recombinant enzyme replacement therapy that is approved in many countries for the treatment of patients with HPP. To address the unmet need for guidance in the monitoring of patients receiving asfotase alfa, an international panel of physicians with experience in diagnosing and managing HPP convened in May 2016 to discuss treatment monitoring parameters. The panel discussions focused on recommendations for assessing and monitoring patients after the decision to treat with asfotase alfa had been made and did not include recommendations for whom to treat. Based on the consensus of panel members, this review provides guidance on the monitoring of patients with HPP during treatment with asfotase alfa, including recommendations for laboratory, efficacy, and safety assessments and the frequency with which these should be performed during the course of treatment. Recommended assessments are based on patient age and include regular monitoring of biochemistry, skeletal radiographs, respiratory function, growth, pain, mobility and motor function, and quality of life. Because of the systemic presentation of HPP, a coordinated, multidisciplinary, team-based, patient-focused approach is recommended in the management of patients receiving asfotase alfa. Monitoring of efficacy and safety outcomes must be tailored to the individual patient, depending on medical history, clinical manifestations, availability of resources in the clinical setting, and the clinician's professional judgment.

Hypophosphatasia: An overview For 2017

Hypophosphatasia (HPP) is the inborn-error-of-metabolism that features low serum alkaline phosphatase (ALP) activity (hypophosphatasemia) caused by loss-of-function mutation(s) of the gene that encodes the tissue-nonspecific isoenzyme of ALP (TNSALP). Autosomal recessive or autosomal dominant inheritance from among >300 TNSALP (ALPL) mutations largely explains HPP's remarkably broad-ranging severity. TNSALP is a cell-surface homodimeric phosphohydrolase richly expressed in the skeleton, liver, kidney, and developing teeth. In HPP, TNSALP substrates accumulate extracellularly. Among them is inorganic pyrophosphate (PPi), a potent inhibitor of mineralization. Superabundance of extracellular PPi explains the hard tissue complications of HPP that feature premature loss of deciduous teeth and often rickets or osteomalacia as well as calcific arthropathies in some affected adults. In infants with severe HPP, blocked entry of minerals into the skeleton can cause hypercalcemia, and insufficient hydrolysis of pyridoxal 5'-phosphate (PLP), the major circulating form of vitamin B₆, can cause pyridoxine-dependent seizures. Elevated circulating PLP is a sensitive and specific biochemical marker for HPP. Also, the TNSALP substrate phosphoethanolamine (PEA) is usually elevated in serum and urine in HPP, though less reliably for diagnosis. Pathognomonic radiographic changes occur in pediatric HPP when the skeletal disease is severe. TNSALP mutation analysis is essential for recurrence risk assessment for HPP in future pregnancies and for prenatal diagnosis. HPP was the final rickets/osteomalacia to have a medical treatment. Now, significant successes using asfotase alfa, a mineral-targeted recombinant TNSALP, are published concerning severely affected newborns, infants, and children. Asfotase alfa was approved by regulatory agencies multinationally in 2015 typically for pediatric-onset HPP.

Neonatal fractures as a presenting feature of LMOD3-associated congenital myopathy

Nemaline myopathy is a rare inherited disorder characterized by weakness, hypotonia, and depressed deep tendon reflexes. It is clinically and genetically heterogeneous, with the most severe phenotype presenting as perinatal akinesia, severe muscle weakness, feeding difficulties and respiratory failure, leading to early mortality. Pathogenic variants in 12 genes, encoding components of the sarcomere or factors related to myogenesis, have been reported in patients affected with the disorder. Here, we describe an early, lethal presentation of decreased fetal movements, hypotonia, muscle weakness, and neonatal respiratory failure requiring ventilator support in three siblings from a consanguineous family. All exhibited perinatal fractures, and thus, a skeletal dysplasia was considered as possibly contributing to the phenotype. However, whole exome sequencing revealed a homozygous, loss-of-function pathogenic variant in LMOD3, which has recently been associated with nemaline myopathy and, in a subset of patients, perinatal fractures. This case demonstrates the importance of considering congenital neuromuscular disorders in the differential diagnosis of perinatal fractures.

[Hypophosphatasia: Clinical manifestations, diagnostic recommendations and therapeutic options]

Hypophosphatasia is a very rare bone metabolism disorder caused by a deficiency in alkaline phosphatase activity, due to mutations in the ALPL gene. Its clinical hallmark is the impairment of skeletal and teeth mineralisation, although extra-skeletal manifestations are frequent. Its phenotypic spectrum is widely variable from a subtype with exclusive odontological impairment (odontohypophosphatasia) to five subtypes with systemic involvement, classified according to the age at the onset of the first symptoms (four of them in the paediatric age range: perinatal lethal, perinatal benign, infant and childhood hypophosphatasia). Those subtypes of hypophosphatasia with an earliest onset usually involve a worse prognosis, due to the risk of developing potentially lethal complications, such as seizures or severe respiratory insufficiency, secondary to rib cage malformations. Due to the extremely low prevalence of the severe forms of hypophosphatasia, its clinical variability and overlapping phenotypic features with several more prevalent conditions, the diagnosis of hypophosphatasia in the clinical setting is challenging. However, its potential lethality and impact on the patient's quality of life, along with the recent availability of an enzyme replacement therapy, increases the relevance of the early and accurate identification of patients affected with hypophosphatasia. On the basis of published evidence and clinical experience, this article suggests an algorithm with practical recommendations for the differential diagnosis of childhood hypophosphatasia, as well as an updated review of current therapeutic options.

Hypophosphatasia - aetiology, nosology, pathogenesis, diagnosis and treatment

Hypophosphatasia is the inborn error of metabolism characterized by low serum alkaline phosphatase activity (hypophosphatasaemia). This biochemical hallmark reflects loss-of-function mutations within the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). TNSALP is a cell-surface homodimeric phosphohydrolase that is richly expressed in the skeleton, liver, kidney and developing teeth. In hypophosphatasia, extracellular accumulation of TNSALP natural substrates includes inorganic pyrophosphate, an inhibitor of mineralization, which explains the dento-osseous and arthritic complications featuring tooth loss, rickets or osteomalacia, and calcific arthopathies. Severely affected infants sometimes also have hypercalcaemia and hyperphosphataemia due to the blocked entry of minerals into the skeleton, and pyridoxine-dependent seizures from insufficient extracellular hydrolysis of pyridoxal 5'-phosphate, the major circulating form of vitamin B6, required for neurotransmitter synthesis. Autosomal recessive or dominant inheritance from ~300 predominantly missense ALPL (also known as TNSALP) mutations largely accounts for the remarkably broad-ranging expressivity of hypophosphatasia. High serum concentrations of pyridoxal 5'-phosphate represent a sensitive and specific biochemical marker for hypophosphatasia. Also, phosphoethanolamine levels are usually elevated in serum and urine, though less reliably for diagnosis. TNSALP mutation detection is important for recurrence risk assessment and prenatal diagnosis. Diagnosing paediatric hypophosphatasia is aided by pathognomic radiographic changes when the skeletal disease is severe. Hypophosphatasia was the last type of rickets or osteomalacia to await a medical treatment. Now, significant successes for severely affected paediatric patients are recognized using asfotase alfa, a bone-targeted recombinant TNSALP.

Hypophosphatasia: an overview of the disease and its treatment

This review presents the current knowledge on hypophosphatasia, a rare genetic disease of very variable severity (from lethal to mild) and clinical presentation, caused by defective production of tissue-non-specific alkaline phosphatase (TNSALP). Hypophosphatasia can affect babies in utero as well as infants, children, and adults. The article first presents the genetics of TNSALP and its many known mutations underlying the disease. Then, it presents the epidemiology, classification, and clinical presentation of the six different forms of the disease (perinatal lethal, prenatal benign, infantile, childhood, adult, and odontohypophosphatasia) as well as the essential diagnostic clues. The last section on treatment presents a survey of the therapeutic approaches, up to the ongoing phase 2 studies of enzyme replacement therapy.

Prevention of Lethal Murine Hypophosphatasia by Neonatal Ex Vivo Gene Therapy Using Lentivirally Transduced Bone Marrow Cells

Hypophosphatasia (HPP) is an inherited skeletal and dental disease caused by loss-of-function mutations in the gene that encodes tissue-nonspecific alkaline phosphatase (TNALP). The major symptoms of severe forms of the disease are bone defects, respiratory insufficiency, and epileptic seizures. In 2015, enzyme replacement therapy (ERT) using recombinant bone-targeted TNALP with deca-aspartate (D10) motif was approved to treat pediatric HPP patients in Japan, Canada, and Europe. However, the ERT requires repeated subcutaneous administration of the enzyme because of the short half-life in serum. In the present study, we evaluated the feasibility of neonatal ex vivo gene therapy in TNALP knockout (Akp2(-/-)) HPP mice using lentivirally transduced bone marrow cells (BMC) expressing bone-targeted TNALP in which a D10 sequence was linked to the C-terminus of soluble TNALP (TNALP-D10). The Akp2(-/-) mice usually die within 20 days because of growth failure, epileptic seizures, and hypomineralization. However, an intravenous transplantation of BMC expressing TNALP-D10 (ALP-BMC) into neonatal Akp2(-/-) mice prolonged survival of the mice with improved bone mineralization compared with untransduced BMC-transplanted Akp2(-/-) mice. The treated Akp2(-/-) mice were normal in appearance and experienced no seizures during the experimental period. The lentivirally transduced BMC were efficiently engrafted in the recipient mice and supplied TNALP-D10 continuously at a therapeutic level for at least 3 months. Moreover, TNALP-D10 overexpression did not affect multilineage reconstitution in the recipient mice. The plasma ALP activity was sustained at high levels in the treated mice, and tissue ALP activity was selectively detected on bone surfaces, not in the kidneys or other organs. No ectopic calcification was observed in the ALP-BMC-treated mice. These results indicate that lentivirally transduced BMC can serve as a reservoir for stem cell-based ERT to rescue the Akp2(-/-) phenotype. Neonatal ex vivo gene therapy thus appears to be a possible treatment option for treating severe HPP.

Clinical spectrum of hypophosphatasia diagnosed in adults

The presentation of hypophosphatasia (HPP) diagnosed in adults demonstrates a wide range of clinical manifestations, many of which are nonspecific. We sought to assess clinical characteristics of adult HPP by evaluation of Mayo Clinic Rochester adults diagnosed with HPP from 1976 through 2008. Subjects were identified by diagnostic code or medical records. Inclusion criteria were age ≥18 years at diagnosis; low serum alkaline phosphatase (AP) without bisphosphonate therapy; and one additional element: elevated pyridoxal 5'-phosphate (PLP) or urine phosphoethanolamine (PEA), evidence of osteomalacia, or family history. We were unable to distinguish manifesting carriers from silent unaffected carriers due to lack of a prospective standardized clinical evaluation and the absence of genetic testing. HPP was diagnosed in 22 unrelated adults (median age 49 years; 68% women). Most patients (68%) were symptomatic at presentation with features including musculoskeletal pain (41%) or incident fracture (18%). A history of fracture was present in 54%: hip/femoral neck (23%), feet (23%, all women), wrist (18%), and spine (9%, all men). Nine patients (36%) had multiple fractures while 4 (all women) had subtrochanteric femur fractures. Radiographic chondrocalcinosis (27%) and documented pyrophosphate arthropathy (14%) were only observed in women. Median minimum serum AP was 43% below the lower normal limit. Urine PEA was elevated in 15/16 patients (94%). PLP median was 68 μg/L (normal, 5-50 μg/L) and all (n=8) were above normal. Symptomatic subjects had more fractures and chondrocalcinosis, lower median minimum AP and PLP and higher median PEA levels. Clinical features more common in fracture patients included symptoms at presentation, history of childhood rickets, dental abnormalities, lower median minimum AP and PLP, and higher median urine PEA. Four subjects had iliac crest bone biopsies, with 2/4 specimens consistent with osteomalacia. These results suggest that adult HPP demonstrates a wide spectrum of clinical manifestations including musculoskeletal pain, fractures, chondrocalcinosis and dental anomalies with some overlap in laboratory characteristics in relationship to disease severity. In addition to genetic and environmental factors, gender may influence the clinical expression of HPP.

Hypophosphatasia: nonlethal disease despite skeletal presentation in utero (17 new cases and literature review)

Hypophosphatasia (HPP) is caused by deactivating mutation(s) within the gene that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Patients manifest rickets or osteomalacia and dental disease ranging from absence of skeletal mineralization in utero to only loss of adult dentition. Until recently, HPP skeletal disease in utero was thought to always predict a lethal outcome. However, several reports beginning in 1999 emphasized a benign prenatal form of HPP (BP-HPP) where skeletal disease detected in utero had a mild postnatal course. Here we describe prenatal and postnatal findings of 17 additional BP-HPP patients among our 178 pediatric HPP patients. Their findings are compared with those of their siblings with HPP, carrier parents, and others with identical TNSALP mutations. New information concerning 7 previously published BP-HPP patients accompanies a review of the HPP literature. Among our 17 BP-HPP patients, prenatal ultrasound showed normal chest or abdominal circumferences where recorded. Sometimes, poor skeletal mineralization, fetal crowding, and third-trimester improvement were observed. Postnatally, extremity bowing further improved (13 patients). BP-HPP severity postnatally spanned the "infantile" to "odonto" HPP phenotypes, resembling our patients who harbored identical TNSALP mutation(s). Eight had autosomal dominant (AD) and 9 had autosomal recessive (AR) BP-HPP. Fourteen of our 15 mothers were HPP carriers or affected. Of the 41 cumulative BP-HPP patients (24 literature cases meriting a BP-HPP diagnosis since 1996 plus our 17 patients), 63% had AR BP-HPP. Maternally transmitted HPP involved 11 of the 13 total AD BP-HPP probands (p = 0.01), supporting a maternal in utero effect on the baby. Fetal crowding, normal fetal mineralization and chest size, and TNSALP heterozygosity seem to identify BP-HPP. However, bowed fetal long bones with AR HPP, specific TNSALP mutations, or poor skeletal mineralization before the third trimester do not reliably diagnose HPP lethality.

Genetic Etiology and Dental Pulp Cell Deficiency of Hypophosphatasia

Hypophosphatasia is caused by mutations of the tissue-non-specific alkaline phosphatase ( TNSALP) gene with deficiency of dentin structure. The aim of this study was to examine whether TNSALP mutation in dental pulp cells contributes to dentin dysplasia in hypophosphatasia. Mutation analysis showed that compound heterozygous mutations of TNSALP were identified in three hypophosphatasia patients, including 3 novel mutation sites. Exfoliated teeth from the patients showed abnormal dentin mineralization and loss of cementum, as assessed by ground sections and scanning electron microscope analysis. Dental pulp cells isolated from one of the patients showed a significantly reduced TNSALP activity and mineralization capacity when compared with those in dental pulp cells from the unaffected individuals. Our results suggested that dentin dysplasia in hypophosphatasia may be associated with the decreased mineralization ability of dental pulp cells.

Whole-body MRI in the childhood form of hypophosphatasia

Hypophosphatasia (HPP) is a rare inborn error of bone metabolism caused by various defects in the gene coding for the tissue-nonspecific alkaline phosphatase (TNSAP). It results in a reduced activity of the TNSAP and elevated concentrations of its substrates, including inorganic pyrophosphate. Clinical features of HPP include defective bone mineralisation with bone deformities, fractures and chronic non-bacterial osteomyelitis. Renal damage due to calcification, craniosynostosis and dental abnormalities with premature loss of dentition are further complications. Until now, detailed descriptions of whole-body magnetic resonance imaging (WB-MRI) in HPP do not exist. Here, we analysed WB-MRIs of 4 children with the childhood form of HPP. Deformities and defects of the long bones could be seen. All patients showed radiological lesions in the metaphyses of the long bones predominantly in the lower extremities being consistent with hyperaemia and oedema. Differential diagnosis includes an inflammatory process being active in these locations.

Clinical characteristics of perinatal lethal hypophosphatasia: a report of 6 cases

Hypophosphatasia is a rare inherited disorder caused by deficient tissue-nonspecific alkaline phosphatase activity. It is classified into 6 subtypes, and the perinatal lethal form of hypophosphatasia is the most severe. Patients with this form suffer from various symptoms, including respiratory failure, premature craniosynostosis, rachitic changes in the metaphyses, convulsions and hypercalcemia. This report presents 6 cases of the perinatal lethal form of hypophosphatasia. All of the patients showed shortening of the long bones in utero in ultrasonographic examinations. Two of the six patients died at birth because they could not establish spontaneous breathing. Three of the remaining four patients also died before 1 yr of age. The major cause of death was respiratory failure due to hypoplastic lung. All of the patients, except for the two who died at birth, experienced convulsions in their clinical courses. Vitamin B6 therapy effectively reduced the frequency and severity of convulsions. However, it could not always make the patients convulsion free. Three patients underwent a genetic analysis. The 1559delT mutation, which abolishes Alkaline Phosphatase (ALP) activity, was a hot spot. A homozygous 1559delT mutation was observed in two patients. However, they differed in severity of symptoms. Although a good genotype-phenotype correlation has been reported in hypophosphatasia, the genotype alone does not always predict the life span of the patients. These cases therefore suggested the importance of genetic counseling.

Hypophosphatasia may lead to bone fragility: don't miss it

Hypophosphatasia is an inheritable disorder characterised by defective bone mineralisation due to the impaired activity of tissue-non-specific alkaline phosphatase (AP). Clinical presentation ranges from stillbirth without mineralised bone to pathological fractures in late adulthood. During childhood, the main manifestations include rickets, growth delay and dental problems. Fractures and bone pain usually characterise the adult form. A 9-year-old girl was referred for repetitive fractures after minimal trauma. She had normal growth, normal sclerae, no rickets and minimal dental abnormalities. Her sister had also presented fractures. The proband, her sister and mother had low total and bone-specific AP levels and E435K mutation in exon 12 of the liver/bone/kidney AP gene. Low AP levels must lead to genetic analysis. Bone fragility and repetitive fractures may be symptoms of hypophosphatasia in childhood, which must not be neglected. Associated factors such as vitamin D or calcium deficiency must be prevented. In conclusion, hypophosphatasia must not be forgotten as an aetiological factor of repetitive fractures or bone pain in children and AP activity should be checked accurately.

Neurosurgical aspects of childhood hypophosphatasia

OBJECTIVE

Hypophosphatasia (HPP; MIM241510) is a rare inborn error of bone metabolism of recessive inheritance. It is caused by mutations in the gene encoding the tissue-nonspecific alkaline phosphatase. Apart from problems in bone mineralization, growth failure, and premature loss of decidual teeth, the infantile and the childhood types of HPP are associated with premature fusion of cranial sutures.

PATIENTS

We report on seven children affected with infantile and childhood HPP who presented with craniosynostosis.

RESULTS

Neurosurgical intervention was necessary in four of them because of intracranial hypertension. In one of these, severe dural calcification posed an unexpected problem during surgery. Secondary ectopia of the cerebellar tonsils were detected in five of the seven patients and caused hydrosyringomyelia in one of them.

CONCLUSIONS

Since cranial sutures are frequently involved in infantile and childhood HPP, a multidisciplinary approach for the clinical care is necessary, including long-term neurosurgical surveillance.

Hypophosphatasia

Hypophosphatasia is a rare inherited disorder characterized by defective bone and tooth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The frequency of the disease has been estimated to be one in 100 000 for severe forms, but mild forms of hypophosphatasia may be more common. The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early tooth loss without bone symptoms. The transmission of severe forms is autosomal recessive, while milder forms may be transmitted as dominant or recessive autosomal traits. The diagnosis is based on serum alkaline phosphatase assay and molecular analysis of the liver/bone/kidney alkaline phosphatase gene (ALPL). Currently, there is no treatment for the disease. Over the past 10 years, great progress has been made in understanding the structure of tissue non-specific alkaline phosphatase, its function in bone mineralization, and the effect of ALPL mutations responsible for hypophosphatasia.

Hypophosphatasia

Hypophosphatasia is a rare inherited disorder characterized by defective bone and teeth mineralization, and deficiency of serum and bone alkaline phosphatase activity. The prevalence of severe forms of the disease has been estimated at 1/100 000.

The symptoms are highly variable in their clinical expression, which ranges from stillbirth without mineralized bone to early loss of teeth without bone symptoms. Depending on the age at diagnosis, six clinical forms are currently recognized: perinatal (lethal), perinatal benign, infantile, childhood, adult and odontohypophosphatasia. In the lethal perinatal form, the patients show markedly impaired mineralization in utero. In the prenatal benign form these symptoms are spontaneously improved. Clinical symptoms of the infantile form are respiratory complications, premature craniosynostosis, widespread demineralization and rachitic changes in the metaphyses. The childhood form is characterized by skeletal deformities, short stature, and waddling gait, and the adult form by stress fractures, thigh pain, chondrocalcinosis and marked osteoarthropathy. Odontohypophosphatasia is characterized by premature exfoliation of fully rooted primary teeth and/or severe dental caries, often not associated with abnormalities of the skeletal system.

The disease is due to mutations in the liver/bone/kidney alkaline phosphatase gene (ALPL; OMIM# 171760) encoding the tissue-nonspecific alkaline phosphatase (TNAP). The diagnosis is based on laboratory assays and DNA sequencing of the ALPL gene. Serum alkaline phosphatase (AP) activity is markedly reduced in hypophosphatasia, while urinary phosphoethanolamine (PEA) is increased. By using sequencing, approximately 95% of mutations are detected in severe (perinatal and infantile) hypophosphatasia.

Genetic counseling of the disease is complicated by the variable inheritance pattern (autosomal dominant or autosomal recessive), the existence of the uncommon prenatal benign form, and by incomplete penetrance of the trait. Prenatal assessment of severe hypophosphatasia by mutation analysis of chorionic villus DNA is possible. There is no curative treatment for hypophosphatasia, but symptomatic treatments such as non-steroidal anti-inflammatory drugs or teriparatide have been shown to be of benefit. Enzyme replacement therapy will be certainly the most promising challenge of the next few years.

Specific osseous spurs in a lethal form of hypophosphatasia correlated with 3D prenatal ultrasonographic images

BACKGROUND

Hypophosphatasia is an osseous dysplasia with highly variable clinical expression, ranging from a recessive lethal prenatal type to late onset dominant short stature with premature shedding of teeth. Lethal forms of hypophosphatasia include short limb dwarfism with lack of ossification, especially on the vertebral bodies, very slender ribs and clavicles, and bowed, short lower extremities, with a bifid aspect of the diaphyses. Alkaline phosphatase is abnormally low in liver, bone, kidney and plasma.

METHODS

We present here the prenatal images of a lethal form of hypophosphatasia, diagnosed precociously because of specific osseous spurs in a context of recurrent short limb dwarfism.

RESULTS

Prenatal 3D ultrasonography has shown these spurs as early as 18 weeks. Molecular biology found compound heterozygous mutations in the gene TNSALP.

CONCLUSION

In a context of short limb dwarfism, the search for these specific osseous spurs orient strongly toward the diagnosis of lethal hypophosphatasia.

Homozygosity for TNSALP mutation 1348c>T (Arg433Cys) causes infantile hypophosphatasia manifesting transient disease correction and variably lethal outcome in a kindred of black ancestry

OBJECTIVE

To determine the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP) defect underlying transiently reversible and variably lethal infantile hypophosphatasia (HPP) in a kindred and to characterize HPP prevalence in black people.

STUDY DESIGN

In 1986, we reported temporary correction of severe HPP in an American kindred of black ancestry where "infantile" HPP was fatal in 2 of 3 affected individuals representing 2 sibships. This transient improvement in 1 patient followed efforts to increase TNSALP activity endogenously and suggested dysregulation of the gene (TNSALP). Here, we sequenced the coding exons and splice sites of the kindred's TNSALP alleles and reviewed our 30-year experience with HPP to assess its prevalence in black people.

RESULTS

Homozygosity for TNSALP missense mutation 1348C>T (Arg433Cys) accounted for this kindred's infantile HPP. The TNSALP promoter sequence was normal. Modeling of TNSALP(433Cys) suggested compromise of the catalytic site. Ethnicity was identified for the 119 families with HPP studied in St. Louis, and race was ascertained for an additional 159 of our 235 consult and HPP families worldwide. In this experience, only this family was of black ancestry.

CONCLUSIONS

Infantile HPP from homozygous TNSALP(433Cys) can remit and thus harbor clues regarding the phenotypic variation and perhaps treatment of HPP.

Bilateral transverse (Bowdler) fibular spurs with hypophosphatasia in an adolescent girl

Hypophosphatasia is a clinically heterogeneous inheritable disorder characterized by defective bone mineralization and the deficiency of serum and tissue liver/bone/kidney alkaline phosphatase activities. Due to the mineralization defect of the bones, various skeletal findings can be radiologically observed in hypophosphatasia. Bowing and Bowdler spurs of long bones are the characteristic findings. The Bowdler spurs reported on in the previous pertinent literature were observed in the perinatal aged patients and these lesions have rarely involved adolescents. We herein report on a 14-year-old girl with fibular Bowdler spurs.

[Childhood hypophosphatasia: a case report due to a novel mutation]

Hypophosphatasia is characterized by defective bone mineralization associated with impaired activity of the tissue non-specific alkaline phosphatase (TNSALP) due to mutations in the TNSALP gene. We describe a child with a mutation that has not been described up to now.

CASE REPORT

A 4-year-old child presented with clinical symptoms of rickets and premature loss of decideous teeth. Reduced serum alkaline phosphatase activity and radiographic features led to the diagnosis of hypophosphatasia, which was confirmed by genetic investigation. The molecular study showed two missense mutations, of which one is a novel mutation.

CONCLUSION

Hypophosphatasia is suspected in a child with rickets and premature loss of decideous teeth. Such symptoms should prompt the search of a reduced serum alkaline phosphatase activity. The clinical and molecular diagnosis of the disease is important for the genetic counseling but also for a proper determination of prognosis, as it is related to the type of mutation.

Pyridoxine-dependent seizures associated with hypophosphatasia in a newborn

Pyridoxine dependency and congenital hypophosphatasia are unusual metabolic disorders. We report a female infant born from healthy consanguineous parents with shortening of limbs, detected during pregnancy by ultrasonography. Immediately after delivery, the baby was admitted to the neonatal intensive care unit because of respiratory distress. A bone radiograph showed hypomineralization of all bones, and serum alkaline phosphatase was very low (10 U/L). Within the first day of life, seizures (focal clonic and tonic) started. The seizures were refractory to phenobarbital and other antiepileptic drugs. The first electroencephalogram (EEG) showed a burst-suppression pattern. Pyridoxine was administered (50 mg/kg) and completely controlled the seizures. Antiepileptic drugs were discontinued, and a maintenance dose of pyridoxine (10 mg/day) was established. A postpyridoxine EEG revealed the disappearance of the burst-suppression pattern. The patient died at age 26 days. Pyridoxine-dependent seizures, when recognized early and treated, have a more favorable prognosis. However, hypophosphatasia detected at birth almost always has a lethal outcome.

Prenatal diagnosis of kyphomelic dysplasia

Kyphomelic dysplasia (KD) is a rare autosomal recessive entity characterized by disproportionate dwarfism with shortening and bowing of the limbs, narrow chest, 11 ribs and metaphyseal flaring. Mental development is generally normal. We report the in utero ultrasound appearances and post-mortem radiographic findings of a 22-week-old male fetus suggestive of KD. A review of 19 previously reported patients with KD is also presented.

Neutrophil alkaline phosphatase (NAP) score in the diagnosis of hypophosphatasia

Hypophosphatasia is an inherited disease characterised by low tissue non-specific alkaline phosphatase (TNSALP) levels and skeletal defects. Diagnosis is usually made by measurement of serum total alkaline phosphatase (TALP, reference range 40-130 iu/l) and pyridoxal-5'-phosphate (PLP), and urine phosphoethanolamine (PEA). Neutrophil alkaline phosphatase (NAP) scores (reference range 20-150) have been reported to be low in isolated cases, but no comparison has been made of the diagnostic value of NAP, TALP, PEA and PLP in hypophosphatasia. We undertook such a comparison in six families with hypophosphatasia. In four families (Families 1, 2, 5, 6) with the adult type of hypophosphatasia, inherited as autosomal dominant, the NAP score and TALP (<40 iu/l), were low, <20 and <40 iu/l respectively, in all affected subjects, though the PEA and PLP were not consistently abnormal. In one of the two families (Family 3) with the autosomal recessive type of hypophosphatasia an affected subject had low NAP as well as low TALP, PLP and PEA. In another family (Family 4) one of the heterozygotes had a low NAP while the other had a normal NAP score (45). A child in this family had a normal TALP level. Her low NAP score (15) supported her to be a possible heterozygote. NAP score is readily available from most laboratories and may be diagnostically helpful in hypophosphatasia.

Kyphomelic dysplasia: a rare form of semilethal skeletal dysplasia

Kyphomelic dysplasia is a rare form of generalized skeletal dysplasia with about 15 cases described so far in the literature. We present the clinical, radiological, and pathological findings of an antenatally detected female fetus affected with this disorder. The differential diagnoses of prenatal and perinatal semilethal skeletal dysplasias and salient features of documented cases of kyphomelic dysplasia are presented.

Mild hypophosphatasia mimicking severe osteogenesis imperfecta in utero: bent but not broken

We describe a fifth instance of hypophosphatasia presenting with prenatal findings suggestive of a very severe bone dysplasia but with a subsequently benign course. Spontaneous improvement of long-bone angulation began prenatally. The postnatal course has been encouraging. This sixth clinical form of hypophosphatasia, which we suggest should be called the benign prenatal form of hypophosphatasia, should be added to the differential diagnostic possibilities considered when angulation or bowing of long bones is discovered prenatally.

Bone metabolism and bone mineral density in childhood hypophosphatasia

Childhood hypophosphatasia (HP) is an inborn error of bone metabolism, characterized by a reduced tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Bone mineral density (BMD) in childhood HP has not been reported so far. We measured BMD, in addition to markers of bone metabolism, in 6 boys with childhood HP (age 2-13 years) and in 10 parents and one sibling, each carrying the autosomal-recessive trait. BMD, measured by peripheral quantitative computed tomography (pQCT) and by dual-energy X-ray absorptiometry (DXA), was expressed as standard deviation from the normal mean (Z scores) and compared with bone mineralization by standard X-rays of the same locations. HP was confirmed by low TNSALP and its elevated substrates. In patients, BMD of the total body or spine, measured by DXA, was in the lower normal range. Total BMD of the distal metaphyses of the radius, measured by pQCT, was normal (Z score: mean +1.5). However, trabecular BMD of both radius (Z score: mean +4) and femur was grossly elevated. In parallel, X-rays showed reduced transradiancy of the radial and femoral metaphyses in all patients. In parents of patients with HP, BMD was in the lower normal range. Only one father had a decreased lumbar BMD. The discrepancy in BMD between cortical and trabecular bone of the metaphyses in patients was not present in their relatives. TNSALP levels in all first degree relatives were just below or in the lower normal range. The markers of bone turnover hydroxyproline and free deoxypyridinoline in urine were normal in patients and relatives. Hypermineralization/sclerosis of trabecular bone might serve as a compensation for a mechanically incompetent bony structure due to an impaired mineralization of cartilage caused by the genetic deficiency of alkaline phosphatase.

Genetic analysis of hypophosphatasia

A review is presented of the recent advances in: (i) clinical features, (ii) biochemistry and molecular biology of alkaline phosphatase, (iii) genetic defect in hypophosphatasia, and (iv) prenatal diagnosis. Despite the recent progress, the pathogenesis of hypophosphatasia is far from being elucidated. More clinical cases and further characterization of the alkaline phosphatase gene mutations are needed for better understanding of the clinical spectrum of the entity.

Asymmetric and symmetric long bone bowing in two sibs: an apparently new bone dysplasia

We describe 2 sibs, one with congenital asymmetric long bone bowing and one with congenital symmetric long bone bowing. Other bony abnormalities in these sibs include beaten metal appearance of the skull, dolichomacrocephaly, ocular hypertelorism, and anterior beaking and bone-within-bone appearance of vertebrae. A differential diagnosis including campomelic dysplasia, kyphomelic dysplasia, hypophosphatasia, Grant syndrome, and osteogenesis imperfecta, and a discussion of potential mechanisms of long bone bowing are presented. The condition that these sibs have shares some characteristics of the above bone disorders, but appears to be a separate entity which to our knowledge has not been described previously.

Hypophosphatasia: dental aspects and mode of inheritance

Hypophosphatasia is rare enzymopathy that normally presents within the first few years of life and often has profound effects upon the periodontium. It is a heritable disorder characterised by defective mineralisation of the skeletal and dental structures of the body and a deficiency in the liver/bone/kidney (L/B/K) isoenzyme of alkaline phosphatase (ALP). There has been a tremendous advance in our knowledge of this condition over the last decade due to the advent of highly specific DNA probes and novel microanalytical techniques. This paper aims to review current literature about hypophosphatasia with special reference to the dental aspects of the condition and to shed light upon the controversial area of its mode of genetic inheritance. It is concluded that hypophosphatasia may result from the existence of 2 defective alleles, which alone or in combination may cause the condition. One allele is expressed in an autosomal dominant manner producing milder phenotypic characteristics, whilst the other is expressed in an autosomal recessive manner producing the more severe clinical form that often results in neonatal death. The milder phenotypes may go undiagnosed and the consequence of this in genetic counselling terms is extremely important.

Hypophosphatasia: a family study involving a case diagnosed from gingival crevicular fluid

Hypophosphatasia is an inherited disorder characterized by defective mineralization of the skeletal and dental structures of the body and deficient liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity. There has been a tremendous advance in our knowledge of this condition over the last decade due to the advent of highly specific DNA probes and novel microanalytic techniques. The purpose of this paper is threefold: to review the dental aspects of current literature about this rare condition; to present a case (and family study) that was diagnosed in a 5-yr-old boy from 0.14 microliters of gingival crevicular fluid, using a new ultrasensitive chemiluminescent assay for the enzyme alkaline phosphatase; and to provide strong evidence for an autosomal dominant mode of inheritance.

Phenotypically dissimilar hypophosphatasia in two sibships

Autosomal dominant and autosomal recessive forms of hypophosphatasia have been reported; generally the clinical picture runs true to form in families. In each of 2 kindreds, 2 sibs were clinically affected by hypophosphatasia to a markedly different extent. One set of sibs showed the lethal (perinatal) and infantile forms. The other showed the dental and adult forms. In both families there was consanguinity, albeit distant, and clinical expression in sibs supporting autosomal recessive inheritance.