Could Alerting Physicians for Low Alkaline Phosphatase Levels Be Helpful in Early Diagnosis of Hypophosphatasia?

Screening for Hypophosphatasia in Adult Patients at a Maximum Care Provider-Retrospective Analyses over Fifteen Years

Background/Objectives: Hypophosphatasemia (HPE) may be temporary (tHPE) in the context of severe diseases, such as sepsis or trauma, or it may persist (pHPE), indicating an adult form of hypophosphatasia (HPP; OMIM 171760), a rare metabolic bone disorder caused by pathogenic nucleotide variants (PNVs) in the ALPLgene. The aim of this study was to analyze the role of auxiliary general biomarkers in verifying low alkaline phosphatase (ALP) serum activity level as an alert parameter for PNVs in the ALPLgene, which are indicative of HPP. In this retrospective analysis, we examined adult patients with an ALP serum activity level below 21 U/L. The cohort comprised 88 patients with temporary HPE (tHPE group) and 20 patients with persistent HPE who underwent re-examination. Genetic analysis performed on 12 pHPE patients identified PNV in the ALPLgene in 11 cases (ALPL group). Hemoglobin [HB], aspartate aminotransferase [AST], gamma-glutamyl transferase [GGT], calcium, phosphate, thyrotropin [TSH], albumin, total protein, and C-reactive protein [CRP] levels represented basic biomarkers. A comparative analysis between groups employed a Student's t-test, and a Student's t-test with bootstrap sampling (n = 10.000) was performed. Results: The mean HB, ALP, calcium, albumin, and total protein levels were lower in the tHPE group compared with the ALPL group (p < 0.01). AST and CRP were increased in the tHPE group (p < 0.01). The model showed an accuracy of 90% and an AUC of 0.94, which means that it can discern the two groups ~94% of the time. Conclusions: Basic biomarker evaluation effectively supports the interpretation of a decreased ALP serum activity level in the context of suspected HPP. In patients with laboratory HPE and biomarkers within reference, a PNV in the ALPLgene is highly suspected.

Enzyme replacement therapy for hypophosphatasia-The current paradigm

Hypophosphatasia (HPP) is a rare, inherited, and systemic disorder characterized by impaired skeletal mineralization and low tissue nonspecific serum alkaline phosphatase (TNSALP) activity. It is caused by either autosomal recessive or dominant-negative mutations in the gene that encodes TNSALP. The phenotype of HPP is very broad including abnormal bone mineralization, disturbances of calcium and phosphate metabolism, pain, recurrent fracture, short stature, respiratory impairment, developmental delay, tooth loss, seizures, and premature death. Other than supportive care, there has been no disease-specific treatment available for those with HPP. Asfotase alfa is a fully humanized, recombinant enzyme replacement therapy for the management of HPP. It is available in several countries for the treatment of the more severe forms of HPP, namely perinatal and infantile HPP. This review will summarize the preclinical data on asfotase alfa and highlight the data from clinical trials and case reports. These data show the transformative nature of asfotase alfa when administered as part of an interdisciplinary treatment model.

Aetiologies of low alkaline phosphatase in a Canadian Paediatric Tertiary Care Centre

Objectives

Increasingly, laboratories flag low serum alkaline phosphatase (sALP) that are age-and sex-specific in paediatrics. The aim of this study was to report clinical manifestations of paediatric patients with age-and sex-specific low sALP, thereby increasing awareness of its potential aetiologies.

Methods

This retrospective Canadian tertiary care paediatric hospital study assessed all sALP of ambulatory patients aged less than 18 years from 2015 to 2017. The hospital used a Beckman Coulter AU assay to measure sALP and compared values to the Canadian age-and sex-specific reference intervals from CALIPER. All children who had at least one subnormal age-and sex-specific sALP were evaluated. A review of medical charts of included patients was performed and demographic characteristics, medical history and diagnosis were collected, and categorized under groups of medical disorders.

Results

Of 11,874 included patients, 1,001 patients (9.2%) had low sALP. Of those, 48% (485/1,001) had transient low sALP activity and 9.6% (96/1,001) had persistently low sALP. Prolonged immobilization and inflammatory bowel disease represented the main aetiologies for persistently low sALP. Interestingly, 13.5% (13/96) of patients with persistently low sALP had no apparent aetiology.

Conclusions

Our results report aetiologies of low sALP in a Canadian paediatric population using age-and sex-specific Canadian reference ranges. This study highlights that healthcare providers should be aware that a low sALP may have clinical significance and should be repeated if warranted based on further clinical assessment.

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.

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.

Cross-sectional analysis: clinical presentation of children with persistently low ALP levels

OBJECTIVES

Low activity of serum alkaline phosphatase (ALP) is a hallmark of hypophosphatasia (HPP), but low readings of ALP are not always recognized in clinical routine. Understanding the clinical presentations associated with low ALP may contribute to a timelier diagnosis of HPP.

METHODS

Data from paediatric patients with low ALP, excluding patients in intensive care and with oncological/haematological disorders, were analysed. Most recent ALP values, previous diagnoses, medication and relevant symptoms were extracted from patient records at nine specialised centres and analysed descriptively. A relationship between body height and ALP values was scrutinised by linear regression.

RESULTS

Of 370 children, 15 (4.1%) had a diagnosis of HPP. In the subgroup without a diagnosis of HPP, 241 (67.9%) out of 355 patients had one or more medical conditions known to be associated with low serum ALP. Of those, hypothyroidism, malnutrition and steroid administration were most frequent. Characteristic symptoms, particularly, short stature, muscle weakness and delay of motor development were more frequent and ALP values were lower in patients with documented HPP diagnosis compared to patients without diagnosis of HPP (Ø z-scores: -2.52) (interquartile range [IQR] = 0.20) vs. -1.96 (IQR = 0.87). A weak positive linear relationship between z-scores of ALP and body height was identified (p<0.001).

CONCLUSIONS

This analysis of paediatric patient records elucidates a wide range of disorders associated with low ALP activity. In case of additional specific symptoms, HPP should always be considered as a differential diagnosis.

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.

Clinical Significance of Hypophosphatasemia in Children

Low serum alkaline phosphatase (sALP)-hypophosphatasemia-is a characteristic of hypophosphatasia (HPP), but related to several clinical conditions. Here, we evaluated the frequency, persistency and the etiology of hypophosphatasemia in children. In retrospective analyses of sALP measurements from children, evaluated according to in-house constructed age- and sex-specific reference ranges, patients with no normal sALP measurement (Unresolved hypophosphatasemia) were invited for reanalysis. Prospectively, ALP substrates, pyridoxal-5-phosphate (PLP), and phosphoethanolamine (PEA) were measured in patients with persistent hypophosphatasemia. Radiographs and ALPL gene sequencing for HPP were performed to the cases with elevated PEA and/or PLP. From 130,340 sALP measurements of 93,162 patients, hypophosphatasemia was detected in 1404 samples from 867 patients (0.9%). Among them, 745 had at least one normal sALP values in laboratory records, grouped as transient hypophosphatasemia. 75 out of 122 patients with unresolved hypophosphatasemia could be reanalyzed for sALP, of whom PLP and PEA measurements were required in 37 due to persistent hypophosphatasemia. Both PEA and PLP were elevated in 4 patients, and ALPL gene analysis showed heterozygous mutations in 3 patients and homozygous in 1 patient. Elevated PEA with normal PLP were detected in 3 patients, and one had a heterozygous ALPL mutation. Anemia was the most common diagnosis, and upper respiratory tract infections and chronic diseases were more common in transient and unresolved hypophosphatasemia, respectively. In conclusion, reflected persistent hypophosphatasemia frequency was 1/1552 (0.06%) in this large pediatric cohort and, ALPL gene mutations were detected in 13.5% (5/37) of the studied cases. Although biochemical hypophosphatasemia is not uncommon, clinically significant HPP is rare.

Analytical Performance of 10 High-Volume Clinical Chemistry Assays on the Alinity c System

Background

Early access for routine testing with the Alinity c clinical chemistry system (Abbot Laboratories) presented the opportunity to characterize the analytical performance of multiple analytes across clinical laboratories in Europe.

Methods

A total of 8 laboratories from 7 European countries evaluated 10 high-volume chemistry assays on the Alinity c system for imprecision, linearity, and accuracy by method comparison to the routine ARCHITECT (Abbott Laboratories) method.

Results

Within-run precision was less than 4% coefficient of variation (CV), with total imprecision less than 5.6% CV for 5- and 20-day evaluations. Linearity met expectations, and method comparison showed strong correlation between the Alinity and ARCHITECT methods, with overall linear correlation coefficient between 0.980 to 1.000 and slopes of the regression line between 0.963 and 1.034. Mean percentage difference between the results of assays run on the ARCHITECT and the Alinity ranged between -1.7% and 2.15%.

Conclusions

Our results demonstrated acceptable key analytical performance across all assays tested at each participating laboratory.

Standardization in laboratory medicine: Two years' experience from category 1 EQA programs in Spain

Introduction

Standardization is the ability to obtain interchangeable results leading to same medical interpretation. External quality assessment (EQA) is the main support of the on-going harmonization initiatives. Aim of study was to evaluate results obtained from two years category 1 EQA program experience in Spain and determine the impact of applying this type of EQA program on the analytical standardization.

Materials and methods

According to the analytical method, traceability and instrument different groups were established which results were evaluated by calculating mean, coefficient of variation and percent of deviation to the reference value. Analytical performance specifications used to the results' evaluation were derived from biological variation for bias and from the inter-laboratory coefficients of variation found in a previous pilot study.

Results

Only creatinine measured by enzymatic methods gave excellent results, although few laboratories used this method. Creatine kinase and GGT gave good precision and bias in all, but one instrument studied. For the remaining analytes (ALT, ALP, AST, bilirubin, calcium, chloride, glucose, magnesium, potassium, sodium, total protein and urate) some improvement is still necessary to achieve satisfactory standardization in our setting.

Conclusions

The two years of category 1 EQA program experience in Spain have manifested a lack of standardization of 17 most frequent biochemistry tests used in our laboratories. The impact of the information obtained on the lack of standardization is to recommend abandoning methods such as ALT, AST without exogenous pyridoxal phosphate, Jaffe method for creatinine, and do not use non-commutable calibrators, such as aqueous solutions for calcium and sodium.

A MnO2nanosheets–o-phenylenediamine oxidative system for the sensitive fluorescence determination of alkaline phosphatase activity

A MnO₂nanosheets–o-phenylenediamine (OPDA) oxidative system was developed for detecting ALP activity selectively, sensitively and conveniently.