Hypophosphatasia

Severe Hypercalcemia Associated With Perinatal Hypophosphatasia While Receiving Enzyme Replacement Therapy

Hypophosphatasia (HPP) is characterized by defective bone mineralization due to reduced function of tissue-nonspecific alkaline phosphatase (TNSALP) caused by pathogenic ALPL gene variants. Hypercalcemia is more common in the perinatal and infantile forms and may be mitigated or prevented with enzyme replacement therapy asfotase alfa (AA). Here, we report a patient who developed severe hypercalcemia while receiving AA. Hypercalcemia was initially managed with intravenous fluids, dietary calcium restriction, and maximizing AA dose. Despite these measures, she required an additional hospital admission, at which time calcitonin 4 IU/kg every 12 hours was initiated. On this regimen, her calcium normalized without recurrence of severe hypercalcemia. Over the subsequent 8 months, restrictions of calcium intake were slowly lifted, and calcitonin was tapered and discontinued with maintenance of calcium within the normal range. This case underscores the significance of vigilant monitoring of calcium levels and dietary intake in infants diagnosed with HPP. While calcitonin is typically not considered as a sustained treatment for hypercalcemia, the present case illustrates the efficacy of adjunct calcitonin therapy, in conjunction with restricted calcium intake and maximum AA dosing, in managing severe hypercalcemia in an infant with perinatal HPP.

Effects of asfotase alfa on fracture healing of adult patient with hypophosphatasia and literature review

OBJECTIVE

Hypophosphatasia (HPP) is a rare inherited disorder caused by ALPL gene mutations, with fracture nonunion being a serious complication. This study investigated the effects of teriparatide and asfotase alfa (AA) on femoral fracture healing of an adult patient with HPP, accompanied with a literature review.

METHODS

A 37-year-old woman wheelchair-bound was diagnosed with HPP due to an extremely low serum alkaline phosphatase (ALP) level (4-10 U/L), who suffered from bilateral femur pain and non-union of femoral shaft fractures on both sides. Compound heterozygous missense mutations (c.382G > A and c.461C > T) were identified in exon5 of ALPL gene. The patient received teriparatide sequential AA therapy. Serum levels of ALP, β-isomerized carboxy-telopeptide of type I collagen (β-CTX) and procollagen type 1 amino-terminal peptide (P1NP), bone mineral density (BMD) and skeletal X-ray were measured during the treatment. Literature was searched by keywords of "Hypophosphatasia", "HPP", "ALPL", "TNSALP", "ALP" combined with "Asfotase alfa", "AA", "enzyme replacement therapy", and "ERT".

RESULTS

After unsuccessful 6-month teriparatide treatment for femoral fracture, AA treatment was initiated, at a dose of 2 mg/kg, 3 times a week. After the first month of AA treatment, serum ALP level increased from 4 to 9206 U/L, and serum calcium and phosphate levels decreased, with increase in PTH, β-CTX, and P1NP levels. After 4 months of AA treatment, her bone pain significantly alleviated, accompanied by significant shortening of the fracture line. After 10 months of AA therapy, the fracture demonstrated complete healing and the patient could walk independently. BMD at lumbar spine and hips was significantly increased. Among 295 adult patients with HPP reported in the literature, 213 (72.2%) exhibited skeletal-related symptoms and 91 (30.8%) presented with bone fractures. In addition to skeletal manifestations, the patients presented with early tooth loss, muscle weakness and ectopic calcification. AA treatment, spanning 9 weeks to 3 years, has been shown to increase ALP levels, promote fracture healing, improve mobility, and alleviate bone pain.

CONCLUSION

Adult HPP patients mainly present with recurrent or poorly healing fractures, bone pain, and early loss of teeth. AA replacement therapy can effectively promote fracture healing, relieve bone pain, and enhance mobility.

Genetic characterization of a large cohort of individuals with a clinical suspicion of hypophosphatasia in the United States

Hypophosphatasia (HPP) is a rare metabolic disease resulting from variants in ALPL, inherited in an either autosomal recessive or autosomal dominant manner. Sponsored clinical ALPL testing was offered in the US for individuals with a clinical suspicion of HPP. Gene variants were assessed to determine the likelihood of identifying disease-causing variants, uncover genotype-phenotype relationships, and for further understanding of ALPL variants in the US HPP population. Variants were detected by Sanger sequencing and classified as pathogenic or likely pathogenic (P/LP; positive test result), variant(s) of uncertain significance (indeterminate test result), benign or likely benign (negative test result), or no variants (negative test result). Clinical signs/symptoms, age, sex, and family history data were voluntarily reported by participating clinicians and were explored for possible association with the test result. Of 1103 individuals tested, results were positive in 40 %, indeterminate in 5 %, and negative in 55 %. Most positive tests were monoallelic P/LP variants (n = 413). The most frequently identified P/LP variants were c.1133A > T/p.Asp378Val (n = 61), c.571G > A/p.Glu191Lys (n = 47), and c.1250A > G/p.Asn417Ser (n = 44). In total, 23 novel ALPL variants were identified, of which 43 % were P/LP and the most frequent type was missense (74 %). Among the 25 % of participants for whom signs/symptoms were reported, a significant association was observed for those with a family history of HPP signs/symptoms and a positive test result. These data contribute important information on the likelihood of disease-causing ALPL variants in individuals with clinical signs/symptoms of HPP, the importance of family history in HPP testing, distribution of ALPL variants, and identification of novel ALPL variants.

Dental manifestations of hypophosphatasia: translational and clinical advances

Hypophosphatasia (HPP) is an inherited error in metabolism resulting from loss-of-function variants in the ALPL gene, which encodes tissue-nonspecific alkaline phosphatase (TNAP). TNAP plays a crucial role in biomineralization of bones and teeth, in part by reducing levels of inorganic pyrophosphate (PPi), an inhibitor of biomineralization. HPP onset in childhood contributes to rickets, including growth plate defects and impaired growth. In adulthood, osteomalacia from HPP contributes to increased fracture risk. HPP also affects oral health. The dentoalveolar complex, that is, the tooth and supporting connective tissues of the surrounding periodontia, include 4 unique hard tissues: enamel, dentin, cementum, and alveolar bone, and all can be affected by HPP. Premature tooth loss of fully rooted teeth is pathognomonic for HPP. Patients with HPP often have complex oral health issues that require multidisciplinary dental care, potentially involving general or pediatric dentists, periodontists, prosthodontists, and orthodontists. The scientific literature to date has relatively few reports on dental care of individuals with HPP. Animal models to study HPP included global Alpl knockout mice, Alpl mutation knock-in mice, and mice with tissue-specific conditional Alpl ablation, allowing for new studies on pathological mechanisms and treatment effects in dental and skeletal tissues. Enzyme replacement therapy (ERT) in the form of injected, recombinant mineralized tissue-targeted TNAP has been available for nearly a decade and changed the prognosis for those with HPP. However, effects of ERT on dental tissues remain poorly defined and limitations of the current ERT have prompted exploration of gene therapy approaches to treat HPP. Preclinical gene therapy studies are promising and may contribute to improved oral health in HPP.

A Case of Hypophosphatasia Started Enzyme Replacement Therapy Since Babyhood Stage

BACKGROUND

Hypophosphatasia (HPP) is an inherited disease caused by low activity of tissue-nonspecific alkaline phosphatase. Dental characteristics include premature loss of primary teeth, enlarged pulp chambers, and enamel hypoplasia. Although enzyme replacement therapy with asfotase alfa was approved in 2015, there are few reports about the dental outcomes of this treatment.

CASE PRESENTATION

A 1-year-old girl referred to our hospital had already lost two primary teeth at the time of her initial visit. She started enzyme replacement therapy 6 days after birth, and genetic analysis later confirmed the diagnosis of HPP. At the age of 4 years and 7 months, 11 primary teeth had been lost, and some of the exfoliated teeth showed inflammatory root resorption or root fracture. There was also a history of abscess formation in a non-carious primary molar.

CONCLUSIONS

This report suggests that early enzyme replacement therapy may prevent traditional tooth loss in patients with HPP. It also highlights the new challenges posed for dental professionals in providing infection control in large pulp cavities and receding periodontal tissue.

Raman Spectroscopic Analysis of Molecular Structure and Mechanical Properties of Hypophosphatasia Primary Tooth

Mild hypophosphatasia (HPP) can be difficult to distinguish from other bone disorders in the absence of typical symptoms such as the premature loss of primary teeth. Therefore, this study aimed to analyze the crystallinity of hydroxyapatite (HAp) and the three-dimensional structure of collagen in HPP teeth at the molecular level and to search for new biomarkers of HPP. Raman spectroscopy was used to investigate the molecular structure, composition, and mechanical properties of primary teeth from healthy individuals and patients with HPP. The results showed that the crystallinity of HAp decreased and the carbonate apatite content increased in the region near the dentin-enamel junction (DEJ) of HPP primary teeth. X-ray diffraction (XRD) analyses confirmed a decrease in HAp crystallinity near the DEJ, and micro-computed tomography (CT) scanning revealed a decrease in mineral density in this region. These results suggest incomplete calcification in HPP primary dentin and may contribute to the development of diagnostic and therapeutic agents.

Integrated Applied Clinical Pharmacology in the Advancement of Rare and Ultra-Rare Disease Therapeutics

The introduction of safe and effective rare/ultra-rare disease treatments is a focus of many biotherapeutic enterprises. Despite this increased activity, a significant unmet need remains, and the responsibility to meet this need is augmented by enhanced genomic, biologic, medical, analytical, and informatic tools. It is recognized that the development of an effective and safe rare/ultra-rare disease therapeutic faces a number of challenges with an important role noted for clinical pharmacology. Clinical pharmacology is foundationally an integrative discipline which must be embedded in and is interdependent upon understanding the pathogenic biology, clinical presentation, disease progression, and end-point assessment of the disease under study. This manuscript presents an overview and two case examples of this integrative approach, the development of C5-targeted therapeutics for the treatment of generalized myasthenia gravis and asfotase alpha for the treatment of hypophosphatasia. The two presented case examples show the usefulness of understanding the biological drivers and clinical course of a rare disease, having relevant animal models, procuring informative natural history data, importing assessment tools from relevant alternative areas, and using integrated applied clinical pharmacology to inform target engagement, dose, and the cascade of pharmacodynamic and clinical effects that follow. Learnings from these programs include the importance of assuring cross-validation of assays throughout a development program and continued commitment to understanding the relationship among the array of Pd end points and clinical outcomes. Using an integrative approach, substantive work remains to be done to meet the unmet needs of patients with rare/ultra-rare disease.

Clinical Characteristics of Persistent Hypophosphatasemia Uncovered in Adult Patients: A Retrospective Study at a Japanese Tertiary Hospital

Background: Hypophosphatasemia is often overlooked despite its potential to indicate underlying pathologies. The aim of this study was to determine the prevalence of persistent hypophosphatasemia in a large, urban, multi-specialty hospital population and characterize the clinical and laboratory findings in adult patients with this condition. Methods: In this retrospective observational study, the results of 424,434 alkaline phosphatase (ALP) tests in 50,136 patients aged ≥18 years that were performed at Okayama University Hospital between July 2020 and October 2023 were analyzed. Persistent hypophosphatasemia was defined as consistently low ALP levels (≤40 IU/L) for 28 days with a minimum recorded level of ≤35 IU/L. Results: Persistent hypophosphatasemia was detected in 273 patients (0.54% of the tested patients), and the patients with persistent hypophosphatasemia included a higher proportion of females (72.5% vs. 52.9% in the people without persistent hypophosphatasemia; chi-squared test, p < 0.01) and had a younger median age (51 years vs. 63 years; Mann-Whitney U test, p < 0.01) than those in the overall tested population. The common causes of persistent hypophosphatasemia were cancer (30%), glucocorticoid use (21%), and immunosuppressants (16%). Notably, 38 patients (14%) had no apparent cause for low ALP values. These patients were categorized on the basis of their clinical characteristics, with some patients presenting symptoms potentially related to adult hypophosphatasia. Conclusions: This study provides prevalence and insights into the causes and characteristics of persistent hypophosphatasemia in a Japanese tertiary care setting. While most cases were associated with known causes, patients with unexplained hypophosphatasemia and symptoms such as chronic pain, muscle weakness, and general fatigue could have adult hypophosphatasia. In such cases, comprehensive evaluation and further investigation for hypophosphatasia should be considered. Persistent hypophosphatasemia of undetermined etiology could be a crucial initial step in diagnostic algorithms for this condition.

Pain, quality of life, and integral management in a cohort of patients diagnosed with hypophosphatasia in Colombia

BACKGROUND

Hypophosphatasia (HPP; OMIM 241510, 241500, and 146300) is a progressive metabolic, genetic disease with wide clinical heterogeneity, ranging from perinatal lethality to mild or moderate localized symptoms. This study aims to analyze the perception of pain, quality of life, and access barriers to healthcare among patients diagnosed with hypophosphatasia in Colombia. In this document we present pain and quality of life results.

METHODS

This study is an observational cohort of 18 HPP patients registered in the Colombian Association of Patients with Lysosomal Storage Diseases and Other Orphan Diseases (ACOPEL) database. We conducted a descriptive analysis using data from three questionnaires (SF-36, Brief Pain Questionnaire (BPQ), and Hypophosphatasia Impact Patient Survey (HIPS); the latter was translated into Spanish and validated for this study.

RESULTS

The most affected features, according to the SF-36 questionnaire, were overall health, vitality, and pain, with a median score above 67%. Patients' perception of their health status (HIPS questionnaire) was favorable, with 38.9% of cases reporting excellent health. On average, results from the BPQ indicated mild to moderate intensity of current pain experienced by patients. Consistency was observed in the reports of either the absence of pain or the presence of mild to moderate intensity when analyzing the results of the three questionnaires.

CONCLUSIONS

Colombian patients with HPP experience mild to moderate impairment in quality of life and pain that interfere with their daily activities. However, there is wide variability in the results obtained.

New insights into the landscape of ALPL gene variants in patients with hypophosphatasia from the Global HPP Registry

Hypophosphatasia (HPP) is a rare, inherited metabolic disease characterized by low tissue-nonspecific alkaline phosphatase activity due to ALPL gene variants. We describe ALPL variants from the observational, prospective, multinational Global HPP Registry. Inclusion in the analysis required a diagnosis of HPP, low serum ALP activity, and ≥1 ALPL variant. Of 1176 patients enrolled as of September 2022, 814 met inclusion criteria in Europe (48.9%), North America (36.7%), Japan (10.2%), Australia (2.6%), and elsewhere (1.6%). Most patients (74.7%) had 1 ALPL variant; 25.3% had ≥2 variants. Nearly all patients (95.6%) had known disease-causing variants; 4.4% had variants of uncertain significance. Disease-causing variants were predominantly missense (770/1556 alleles). The most common variants were c.571G>A (102/1628 alleles), c.1250A>G (66/1628 alleles), and c.1559del (61/1628 alleles). Variant profiles were generally consistent, except in Japan, where a higher proportion of patients (68.7%) had ≥2 ALPL variants, likely because more had disease onset before age 6 months (53.0% vs. 10.1%-23.1% elsewhere). Frameshift mutations (61/164 alleles) and inframe deletions (7/164 alleles) were more common in Japan. Twenty-three novel variants were discovered, each in a single geographic region, predominantly Europe. Analyses confirmed previously known ALPL variants, identified novel variants, and characterized geographic variation in frequency and type of ALPL variants in a large population.

Diagnosis and initial management of children presenting with premature loss of primary teeth associated with a systemic condition: A scoping review and development of clinical aid

BACKGROUND

Premature loss of primary teeth (PLPT) can be a rare presentation of systemic medical conditions. Premature loss of primary teeth may present a diagnostic dilemma to paediatric dentists.

AIMS

To identify systemic conditions associated with PLPT and develop a clinical aid.

DESIGN

OVID Medline, Embase and Web of Science were searched up to March 2023. Citation searching of review publications occurred. Exclusion occurred for conference abstracts, absence of PLPT and absence of English-language full text.

RESULTS

Seven hundred and ninety-one publications were identified via databases and 476 by citation searching of review articles. Removal of 390 duplicates occurred. Following the exclusion of 466 records on abstract review, 411 publications were sought for retrieval, of which 142 met inclusion criteria. Thirty-one systemic conditions were identified. For 19 conditions, only one publication was identified. The majority of publications, 91% (n = 129), were case reports or series. Most publications, 44% (n = 62), were related to hypophosphatasia, and 25% (n = 35) were related to Papillon-Lefèvre. Diagnostic features were synthesised, and a clinical aid was produced by an iterative consensus approach.

CONCLUSIONS

A diverse range of systemic diseases are associated with PLPT. Evidence quality, however, is low, with most diseases having a low number of supporting cases. This clinical aid supports paediatric dentists in differential diagnosis and onward referral.

Catalyzing precision: unraveling the diagnostic conundrum of tunisian familial hypophosphatasia case through integrative clinical and molecular approaches

Familial Hypophosphatasia presents a complex diagnostic challenge due to its wide-ranging clinical manifestations and genetic heterogeneity. This study aims to elucidate the molecular underpinnings of familial Hypophosphatasia within a Tunisian family harboring a rare c.896 T > C mutation in the ALPL gene, offering insights into genotype-phenotype correlations and potential therapeutic avenues. The study employs a comprehensive approach, integrating biochemical examination, genetic analysis, structural modeling, and functional insights to unravel the impact of this rare mutation. Genetic investigation revealed the presence of the p.Leu299Pro mutation within the ALPL gene in affected family members. This mutation is strategically positioned in proximity to both the catalytic site and the metal-binding domain, suggesting potential functional consequences. Homology modeling techniques were employed to predict the 3D structure of TNSALP, providing insights into the structural context of the mutation. Our findings suggest that the mutation may induce conformational changes in the vicinity of the catalytic site and metal-binding domain, potentially affecting substrate recognition and catalytic efficiency. Molecular dynamics simulations were instrumental in elucidating the dynamic behavior of the tissue-nonspecific alkaline phosphatase isozyme (TNSALP) in the presence of the p.Leu299Pro mutation. The simulations indicated alterations in structural flexibility near the mutation site, with potential ramifications for the enzyme's overall stability and function. These dynamic changes may influence the catalytic efficiency of TNSALP, shedding light on the molecular underpinnings of the observed clinical manifestations within the Tunisian family. The clinical presentation of affected individuals highlighted significant phenotypic heterogeneity, underscoring the complex genotype-phenotype correlations in familial Hypophosphatasia. Variability in age of onset, severity of symptoms, and radiographic features was observed, emphasizing the need for a nuanced understanding of the clinical spectrum associated with the p.Leu299Pro mutation. This study advances our understanding of familial Hypophosphatasia by delineating the molecular consequences of the p.Leu299Pro mutation in the ALPL gene. By integrating genetic, structural, and clinical analyses, we provide insights into disease pathogenesis and lay the groundwork for personalized therapeutic strategies tailored to specific genetic profiles. Our findings underscore the importance of comprehensive genetic and clinical evaluation in guiding precision medicine approaches for familial Hypophosphatasia.

Detection of hypophosphatasia in hospitalised adults in rheumatology and internal medicine departments: a multicentre study over 10 years

INTRODUCTION

Hypophosphatasia (HPP) is a rare genetic disease caused by loss-of-function mutations in the ALPL gene encoding the tissue non-specific alkaline phosphatase (ALP). Mild HPP is usually misdiagnosed in adult age. While an elevated serum ALP value draws more attention than a low value, low serum ALP should be better recognised and may lead to HPP detection.

METHODS

Patients were selected from the records of the biochemistry department of six University Hospitals in France. Patients were hospitalised in the departments of rheumatology and internal medicine between 2007 and 2017.

RESULTS

56 321 hospitalised patients had at least 2 serum ALP dosages and 664 of these patients had at least 2 low serum ALP≤35 UI/L. Among these 664 patients, 482 (72.6%) had fluctuating low values (mean age 62.9 years; 60% of women) and 182 patients (27.4%) had persistent low values below 35 IU/L (mean age 53.4 years; 67% of women). Among patients with persistent hypophosphatasaemia treated with bisphosphonates, 70.8% never had ALP measurement before treatment and 20.8% were treated despite an abnormal decrease of ALP. Genetic testing was performed in 18 patients and was positive in 11. Genetic diagnosis of HPP was at least 6.0% in persistent hypophosphatasaemia and at least 15.9% in patients with at least three symptoms suggestive of HPP.

CONCLUSION

In this 10-year retrospective study, 0.32% of adult patients hospitalised in the rheumatology and internal medicine departments had persistently low serum ALP, and among them, 6% had genetically proven HPP. Reported hypophosphatasaemia represented only 3.6% of hospitalised patients.

A case report of odonto-hypophosphatasia with a novel variant in the ALPL gene

OBJECTIVES

Hypophosphatasia (HPP) is a rare skeletal dysplasia caused by variants in the alkaline phosphatase (ALPL) gene. More than 400 pathogenic variants of the ALPL gene have been registered in the ALPL gene variant database. Here, we describe the case of a Japanese child with odonto-hypophsphatasia (odonto-HPP) and a novel ALPL variant.

CASE PRESENTATION

At the age of 2 years and 1 month, he prematurely lost one deciduous tooth, with the root intact, when he fell and hit his face lightly. Three months later, he lost another adjacent deciduous tooth without incentive. His serum alkaline phosphatase (ALP) level was 72 U/L. His urine phosphoethanolamine (PEA) level was extremely high at 938 μmol/mg·Cre. The serum pyridoxal 5'-phosphaye (PLP) level was 255.9 nmol/L. Based on the clinical symptoms and laboratory findings, the patient was clinically diagnosed with odonto-HPP. Genetic analysis of the ALPL gene revealed a heterozygous variant (NM_000478.6:c.1151C>A, p.Thr384Lys).

CONCLUSIONS

We report a case of odonto-HPP with a novel variant in the ALPL gene. HPP is a rare disease, and the heterozygous mutation in the ALPL gene highlights the novelty of this case.

Mild hypophosphatasia may be twice as prevalent as previously estimated: an effective clinical algorithm to detect undiagnosed cases

OBJECTIVES

Since the prevalence of hypophosphatasia (HPP), a rare genetic disease, seems to be underestimated in clinical practice, in this study, a new diagnostic algorithm to identify missed cases of HPP was developed and implemented.

METHODS

Analytical determinations recorded in the Clinical Analysis Unit of the Hospital Universitario Clínico San Cecilio in the period June 2018 - December 2020 were reviewed. A new clinical algorithm to detect HPP-misdiagnosed cases was used including the following steps: confirmation of persistent hypophosphatasemia, exclusion of secondary causes of hypophosphatasemia, determination of serum pyridoxal-5'-phosphate (PLP) and genetic study of ALPL gene.

RESULTS

Twenty-four subjects were selected to participate in the study and genetic testing was carried out in 20 of them following clinical algorithm criteria. Eighty percent of patients was misdiagnosed with HPP following the current standard clinical practice. Extrapolating these results to the current Spanish population means that there could be up to 27,177 cases of undiagnosed HPP in Spain. In addition, we found a substantial proportion of HPP patients affected by other comorbidities, such as autoimmune diseases (∼40 %).

CONCLUSIONS

This new algorithm was effective in detecting previously undiagnosed cases of HPP, which appears to be twice as prevalent as previously estimated for the European population. In the near future, our algorithm could be globally applied routinely in clinical practice to minimize the underdiagnosis of HPP. Additionally, some relevant findings, such as the high prevalence of autoimmune diseases in HPP-affected patients, should be investigated to better characterize this disorder.

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.

Short stature with low serum alkaline phosphatase activity: a case report of hypophosphatasia

Hypophosphatasia (HPP) is a rare condition characterized by abnormal bone mineralization. The manifestations of HPP vary from no symptoms to intrauterine fetal death; short stature is another indication of HPP. A 3 ½-year-old boy presented with short stature, transient hypercalcemia, and mild gait disturbance without definite bony deformity. Laboratory examination revealed transient hypercalcemia, normal phosphorous and 25-hydroxy vitamin D levels, and mildly low alkaline phosphatase levels. A targeted next-generation sequencing panel associated with inborn errors of metabolism revealed a pathogenic heterozygous mutation in the ALPL gene, c.979T>C (p.Phe327Leu). When a child visits a hospital with short stature, decreased height velocity, and low alkaline phosphatase level, clinicians should consider the possibility of HPP even if definite skeletal dysplasia is not evident.

Could Some Patients With Fibromyalgia Potentially Have Hypophosphatasia? A Retrospective Single-Center Study

OBJECTIVE

Hypophosphatasia (HPP) is a rare disease characterized by incomplete or defective bone mineralization due to a mutation in the alkaline phosphatase (ALP) gene causing low levels of ALP. Disease presentation is heterogeneous and can present as a chronic pain syndrome like fibromyalgia (FM). Our objective was to determine if there are any potential patients with HPP in the group of patients who were diagnosed with FM. Antiresorptive therapy use can trigger atypical femur fractures in patients with HPP.

METHODS

We performed a retrospective chart review of all patients 18 years or older at a single academic center who were diagnosed with FM and had either a low or a normal ALP level. The following characteristics were reviewed: biological sex; age; history of fractures; diagnosis of osteoporosis, osteopenia, osteoarthritis, and chondrocalcinosis; genetic testing; vitamin B6 level testing; and medications.

RESULTS

Six hundred eleven patients with FM were identified. Two hundred had at least one low ALP level, and 57 had at least three consecutively low measurements of ALP, 44% of which had a history of fractures. No patients had vitamin B6 levels checked. None of the patients had previous genetic testing for HPP or underwent testing for zinc or magnesium levels.

CONCLUSION

The percentage of patients with FM who were found to have consistently low ALP levels was 9.3%. None had vitamin B6 level or genetic testing, suggesting that the diagnosis was not suspected. It is important to diagnose HPP given the availability of enzyme replacement therapy to prevent complications from HPP such as fractures. Our data support screening for this condition as a part of the initial workup of FM.

Clinical and molecular description of the first Italian cohort of 33 subjects with hypophosphatasia

Introduction

Hypophosphatasia (HPP) is a rare genetic disease caused by inactivating variants of the ALPL gene. Few data are available on the clinical presentation in Italy and/or on Italian HPP surveys.

Methods

There were 30 suspected HPP patients recruited from different Italian tertiary cares. Biological samples and related clinical, biochemical, and anamnestic data were collected and the ALPL gene sequenced. Search for large genomic deletions at the ALPL locus (1p36) was done. Phylogenetic conservation and modeling were applied to infer the effect of the variants on the protein structure.

Results

There were 21 ALPL variants and one large genomic deletion found in 20 out of 30 patients. Unexpectedly, NGS-driven differential diagnosis allowed uncovering three hidden additional HPP cases, for a total of 33 HPP subjects. Eight out of 24 coding variants were novel and classified as "pathogenic", "likely pathogenic", and "variants of uncertain significance". Bioinformatic analysis confirmed that all the variants strongly destabilize the homodimer structure. There were 10 cases with low ALP and high VitB6 that resulted negative to genetic testing, whereas two positive cases have an unexpected normal ALP value. No association was evident with other biochemical/clinical parameters.

Discussion

We present the survey of HPP Italian patients with the highest ALPL mutation rate so far reported and confirm the complexity of a prompt recognition of the syndrome, mostly for HPP in adults. Low ALP and high VitB6 values are mandatory for the genetic screening, this latter remaining the gold standard not only to confirm the clinical diagnosis but also to make differential diagnosis, to identify carriers, to avoid likely dangerous therapy in unrecognized cases.

A unique case of childhood hypophosphatasia caused by a novel heterozygous 51-bp in-frame deletion in the ALPL gene

Hypophosphatasia (HPP) is caused by inactivating variants of the ALPL gene, which encodes tissue non-specific alkaline phosphatase (TNSALP). Among the six subtypes of HPP, childhood HPP presents after 6 months and before 18 yr of age, and is inherited in both autosomal dominant and autosomal recessive manners. Patients with childhood HPP have variable symptoms, including rickets-like bone changes, low bone mineral density (BMD), short stature, muscle weakness, craniosynostosis, and premature loss of deciduous teeth. Here, we describe a 7-yr-old boy with childhood HPP who showed short stature, impaired ossification of the carpal bones, and low BMD. Genetic testing identified a novel heterozygous 51-bp in-frame deletion in the ALPL gene (c.1482_1532del51), leading to the lack of 17 amino acids between Gly495 and Leu511 (p.Gly495_Leu511del). In vitro transfection experiments revealed the loss of enzymatic activity and the dominant-negative effect of the TNSALP[p.Gly495_Leu511del] variant; thus, the patient was diagnosed as having autosomal dominant HPP. The TNSALP[p.Gly495_Leu511del] variant was localized to the plasma membrane as was the wild-type TNSALP (TNSALP[WT]): however, co-immunoprecipitation experiments suggested a reduced dimerization between TNSALP[p.Gly495_Leu511del] and TNSALP[WT]. This case expands the variable clinical manifestation of childhood HPP and sheds light on the molecular bases underlying the dominant-negative effects of some TNSALP variants.

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.

Not just a carrier: Clinical presentation and management of patients with heterozygous disease-causing alkaline phosphatase (ALPL) variants identified through expanded carrier screening

Hypophosphatasia (HPP) is an underrecognized, complex bone mineralization disorder with variable manifestations caused by one or two deleterious variants in the alkaline phosphatase (ALPL) gene. Expanded carrier screening (ECS), inclusive of ALPL, intends to inform reproductive risk but may incidentally reveal an HPP diagnosis with 50% familial risks. We sought to investigate at-risk individuals and develop a multidisciplinary referral and evaluation protocol for ECS-identified ALPL heterozygosity. A retrospective database query of ECS results from 8 years to 1 month for heterozygous pathogenic/likely pathogenic ALPL variants was completed. We implemented a clinical protocol for diagnostic testing and imaging, counseling, and interdisciplinary care management for identified patients, and outcomes were documented. Heterozygous ALPL variants were identified in 12/2248 unrelated patients undergoing ECS (0.53%; heterozygote frequency 1/187). Of 10 individuals successfully contacted, all demonstrated symptomatology and/or alkaline phosphatase values consistent with HPP. ECS may reveal incidental health risks, including recognition of missed HPP diagnoses in ALPL heterozygotes. In our cohort, all ECS-identified ALPL heterozygotes with clinical and/or biochemical data available demonstrated features of HPP. Referral to a genetics professional familiar with HPP is indicated for family history assessment, genetic counseling, cascade testing, and long-term bone health management.

Dental manifestation and management of hypophosphatasia

Hypophosphatasia is an inherited metabolic disorder characterized by defective mineralization of bones and teeth with a wide variety of manifestations, ranging from stillbirth to dental symptoms alone. Recently, the prognosis of severe hypophosphatasia patients has been greatly improved by the introduction of enzyme replacement therapy. The typical dental manifestation is early exfoliation of primary teeth due to disturbed cementum formation, so dentures are recommended to ensure that important oral functions are acquired. Some studies have shown that enzyme replacement therapy improves dental mineralization, resulting in the stabilization of periodontal tissues and better growth of tooth roots. A nationwide Japanese survey revealed the common genetic and dental manifestations of patients with mild hypophosphatasia, which markedly differ from those of the severe forms. There may be many undiagnosed mild patients, so dentists should contribute to the early diagnosis by screening possible cases based on the typical finding of early exfoliation of primary teeth. Early diagnosis is important for patients to receive early intervention in both medical and dental fields. The establishment of fundamental dental therapy to solve the dental problems is still underway and is eagerly anticipated.

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.

Hereditary Metabolic Bone Diseases: A Review of Pathogenesis, Diagnosis and Management

Hereditary metabolic bone diseases are characterized by genetic abnormalities in skeletal homeostasis and encompass one of the most diverse groups among rare diseases. In this review, we examine 25 selected hereditary metabolic bone diseases and recognized genetic variations of 78 genes that represent each of the three groups, including sclerosing bone disorders, disorders of defective bone mineralization and disorder of bone matrix and cartilage formation. We also review pathophysiology, manifestation and treatment for each disease. Advances in molecular genetics and basic sciences has led to accurate genetic diagnosis and novel effective therapeutic strategies for some diseases. For other diseases, the genetic basis and pathophysiology remain unclear. Further researches are therefore crucial to innovate ways to overcome diagnostic challenges and develop effective treatment options for these orphan diseases.

Dental manifestations in adult hypophosphatasia and their correlation with biomarkers

Hypophosphatasia (HPP) is a genetic condition with broad clinical manifestations caused by alkaline phosphatase (ALP) deficiency. Adults with HPP exhibit a wide spectrum of signs and symptoms. Dental manifestations including premature tooth loss are common. Much of the published literature reporting dental manifestations consists of case reports and series of symptomatic patients, likely biased towards more severe dental manifestations. The objective of this study was to systematically explore the dental manifestations among adults with HPP by conducting a comprehensive dental evaluation. To minimize bias, the study explored dental manifestations in an unselected cohort of adults with HPP. Participants were identified searching electronic health record (EHR) data from a rural health system to discover adults with persistent ALP deficiency. Heterozygotes with pathogenic (P), likely pathogenic (LP), or uncertain variants (VUS) in ALPL and at least one elevated ALP substrate were defined as adults with HPP and underwent genetic, dental, oral radiographic, and biomarker evaluation. Twenty-seven participants completed the study. Premature tooth loss was present in 63% (17/27); 19% (5/27) were missing eight or more teeth. Statistically significant associations were found between premature permanent tooth loss and HPP biomarkers ALP (p = 0.049) and bone-specific ALP (p = 0.006). Serum ALP (ρ = -0.43, p = 0.037) and bone-specific ALP (ρ = -0.57, p = 0.004) were negatively correlated with number of teeth lost prematurely. As noted with tooth loss, periodontal breakdown was associated with bone-specific ALP. An inverse association between periodontal breakdown and bone-specific ALP was observed (p = 0.014). These findings suggest a role for ALP in maintenance of dentition.

Status Epilepticus due to Asfotase Alfa Interruption in Perinatal Severe Hypophosphatasia

BACKGROUND

Hypophosphatasia (HPP), an inherited, metabolic disorder caused by loss-of-function mutations in the ALPL gene, affects not only bone and tooth mineralization but also central nervous system (CNS) function, resulting in vitamin B6/pyridoxine-responsive seizures. Asfotase alfa treatment mainly improves the skeletal manifestations of HPP. As of yet, there are no reports demonstrating seizure exacerbation caused by asfotase alfa interruption.

CASE

The patient was a 2-year and 8-month-old female with clinical and genetic diagnosis of perinatal severe HPP. Genetic analysis of ALPL identified compound heterozygous variants. Asfotase alfa and pyridoxine administration begun on postnatal day 2 restored normal development and suppressed seizures except for simple febrile seizures. From age 2 years when her asfotase alfa injections became irregular, she began experiencing seizure exacerbation, including status epilepticus, leading to acute encephalopathy and severe sequelae. The seizure exacerbations always coincided with low alkaline phosphatase (ALP) activity caused by the interruption of asfotase alfa administration.

DISCUSSION

The clinical course of the present case demonstrated the effect of asfotase alfa on CNS symptoms and a clear correlation between low serum ALP activity and seizure exacerbation. Serum ALP activity measurements were useful as a therapeutic marker in the present case. Furthermore, the risk of seizure exacerbation in the patient could have been predicted, given the genotype-phenotype correlation related to the ALPL gene in the Japanese population.

CONCLUSION

Regular asfotase alfa injections are needed to prevent seizure exacerbation in patients with HPP. Educating patients and their family about the need for regular asfotase alfa treatment is crucial to preventing disease exacerbation.

Dissecting mutational allosteric effects in alkaline phosphatases associated with different Hypophosphatasia phenotypes: An integrative computational investigation

Hypophosphatasia (HPP) is a rare inherited disorder characterized by defective bone mineralization and is highly variable in its clinical phenotype. The disease occurs due to various loss-of-function mutations in ALPL, the gene encoding tissue-nonspecific alkaline phosphatase (TNSALP). In this work, a data-driven and biophysics-based approach is proposed for the large-scale analysis of ALPL mutations-from nonpathogenic to severe HPPs. By using a pipeline of synergistic approaches including sequence-structure analysis, network modeling, elastic network models and atomistic simulations, we characterized allosteric signatures and effects of the ALPL mutations on protein dynamics and function. Statistical analysis of molecular features computed for the ALPL mutations showed a significant difference between the control, mild and severe HPP phenotypes. Molecular dynamics simulations coupled with protein structure network analysis were employed to analyze the effect of single-residue variation on conformational dynamics of TNSALP dimers, and the developed machine learning model suggested that the topological network parameters could serve as a robust indicator of severe mutations. The results indicated that the severity of disease-associated mutations is often linked with mutation-induced modulation of allosteric communications in the protein. This study suggested that ALPL mutations associated with mild and more severe HPPs can exert markedly distinct effects on the protein stability and long-range network communications. By linking the disease phenotypes with dynamic and allosteric molecular signatures, the proposed integrative computational approach enabled to characterize and quantify the allosteric effects of ALPL mutations and role of allostery in the pathogenesis of HPPs.

Genetic Disorders of Calcium and Phosphorus Metabolism

In this review, we describe genetic mutations affecting metabolic pathways of calcium and phosphorus homeostasis. Calcium and phosphorus homeostasis has tight hormonal regulation by three major hormones: vitamin D, parathyroid hormone (PTH) and fibroblast growth factor 23 (FGF23). We describe the physiology and pathophysiology of disorders, their biochemical profile, clinical characteristics, diagnostics, and treatments.

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.

A Reference Range for Plasma Levels of Inorganic Pyrophosphate in Children Using the ATP Sulfurylase Method

PURPOSE

Generalized arterial calcification of infancy, pseudoxanthoma elasticum, autosomal recessive hypophosphatemic rickets type 2, and hypophosphatasia are rare inherited disorders associated with altered plasma levels of inorganic pyrophosphate (PPi). In this study, we aimed to establish a reference range for plasma PPi in the pediatric population, which would be essential to support its use as a biomarker in children with mineralization disorders.

METHODS

Plasma samples were collected from 200 children aged 1 day to 18 years who underwent blood testing for medical conditions not affecting plasma PPi levels. PPi was measured in proband plasma utilizing a validated adenosine triphosphate (ATP) sulfurylase method.

RESULTS

The analytical sensitivity of the ATP sulfurylase assay consisted of 0.15 to 10 µM PPi. Inter- and intra-assay coefficients of variability on identical samples were below 10%. The standard range of PPi in the blood plasma of children and adolescents aged 0 to 18 years was calculated as 2.36 to 4.44 µM, with a median of 3.17 µM, with no difference between male and female probands. PPi plasma levels did not differ significantly in different pediatric age groups.

MAIN CONCLUSIONS

Our results yielded no noteworthy discrepancy to the reported standard range of plasma PPi in adults (2-5 µM). We propose the described ATP sulfurylase method as a diagnostic tool to measure PPi levels in plasma as a biomarker in the pediatric population.

Pain and health-related quality of life in patients with hypophosphatasemia with and without ALPL gene mutations

BACKGROUND

Low serum alkaline phosphatase levels are the hallmark of hypophosphatasia, a disorder due to pathogenic variants of the ALPL gene. However, some patients do not carry ALPL variants and the cause of low alkaline phosphatase remains unknown. We aimed to determine health-related quality of life in adults with low alkaline phosphatase and explore the differences between patients with and without ALPL mutations.

METHODS

We studied 35 adult patients with persistently low alkaline phosphatase unrelated to secondary acquired causes who had ALPL sequenced, and 35 controls of similar age. Three questionnaires about body pain (Brief Pain Inventory, BPI), physical disability (Health Assessment Questionnaire Disability Index, HAQ-DI), and health-related quality of life (36-item Short-Form Health Survey, SF-36) were delivered by telephone interviews.

RESULTS

The mean BPI intensity and interference scores were higher in the patient group (p=0.04 and 0.004, respectively). All domains of the HAQ instrument tended to score better in the control group, with significant differences in the "reach" score (p=0.037) and the overall mean score (0.23 vs 0.09; p=0.029). Patients scored worse than controls in several SF-36 dimensions (Role physical, p=0.039; Bodily pain p=0.046; Role emotional, p=0.025). Patients with and without pathogenic variants scored similarly across all tests, without between-group significant differences.

CONCLUSIONS

Patients with persistently low levels of alkaline phosphatase have significantly worse scores in body pain and other health-related quality of life dimensions, without differences between patients with and without pathogenic variants identified in ALPL gene. This is consistent with the latter ones carrying mutations in regulatory regions.

Clinical, biochemical and genetic findings in adult patients with chronic hypophosphatasemia

PURPOSE

The study aimed to define the clinical, biochemical and genetic features of adult patients with osteopenia/osteoporosis and/or bone fragility and low serum alkaline phosphatase (sALP).

METHODS

Twenty-two patients with at least two sALP values below the reference range were retrospectively enrolled after exclusion of secondary causes. Data about clinical features, mineral and bone markers, serum pyridoxal-5'-phosphate (PLP), urine phosphoethanolamine (PEA), lumbar and femur bone densitometry, and column X-ray were collected. Peripheral blood DNA of each participant was analyzed to detect ALPL gene anomalies.

RESULTS

Pathogenic ALPL variants (pALPL) occurred in 23% and benign variants in 36% of patients (bALPL), while nine patients harbored wild-type alleles (wtALPL). Fragility fractures and dental anomalies were more frequent in patients harboring pALPL and bALPL than in wtALPL patients. Of note, wtALPL patients comprised women treated with tamoxifen for hormone-sensitive breast cancer. Mineral and bone markers were similar in the three groups. Mean urine PEA levels were significantly higher in patients harboring pALPL than those detected in patients harboring bALPL and wtALPL; by contrast, serum PLP levels were similar in the three groups. A 6-points score, considering clinical and biochemical features, was predictive of pALPL detection [P = 0.060, OR 1.92 (95% CI 0.972, 3.794)], and more significantly of pALPL or bALPL [P = 0.025, OR 14.33 (95% CI 1.401, 14.605)].

CONCLUSION

In osteopenic/osteoporotic patients, single clinical or biochemical factors did not distinguish hypophosphatasemic patients harboring pALPL or bALPL from those harboring wtALPL. Occurrence of multiple clinical and biochemical features is predictive of ALPL anomalies, and, therefore, they should be carefully identified. Tamoxifen emerged as a hypophosphatasemic drug.

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.

Dental outcomes for children receiving asfotase alfa for hypophosphatasia

INTRODUCTION

Hypophosphatasia, a genetic disease impeding development of teeth and bones, is associated with premature exfoliation of primary teeth. Hypophosphatasia is caused by mutations in the ALPL gene, which encodes the tissue non-specific form of alkaline phosphatase. Asfotase alfa (Strensiq®) is a human recombinant bone-targeted alkaline phosphatase.

OBJECTIVES

To review development and exfoliation patterns of primary/permanent teeth in a cohort of patients with hypophosphatasia enrolled in an open-label clinical trial of enzyme replacement therapy (ERT) with asfotase alfa.

METHODS

Data were collected from existing study files of a cohort of patients ≤5 years of age with infantile hypophosphatasia. Children were recruited at the Winnipeg site of a global clinical trial and were treated with ERT. Dental information, including the exfoliation/eruption patterns, were recorded at each visit.

RESULTS

Eleven children (7 females, 4 males) participated. Participants enrolled as infants (5 infants; mean age 3.0 ± 2.3 months) prematurely lost significantly fewer teeth to hypophosphatasia than patients recruited as preschoolers (6 preschoolers; mean age 52.5 ± 11.3 months), who started on asfotase alfa at a later age. Conclusion The oral health of children with early onset infantile hypophosphatasia may be improved with early and continued administration of ERT, compared to institution of therapy later in childhood.

Case Report: Variations in the ALPL Gene in Chinese Patients With Hypophosphatasia

Background: Hypophosphatasia (HPP) is an autosomal genetic disorder characterized biochemically by abnormal of bone parameters and serum alkaline phosphatase (ALP) activity as well as clinically by deficiency of teeth and bone mineralization. The clinical presentation is a continuum ranging from a prenatal lethal form with no skeletal mineralization to a mild form with late adult onset presenting with non-pathognomonic symptoms. ALP deficiency is the key to the pathogenesis of abnormal metabolism and skeletal system damage in HPP patients.

Methods: We investigated five patients with skeletal dysplasia in the clinic. Whole-exome sequencing was performed in order to aid diagnosis of the patients.

Results: Eight variants in the ALPL gene in the five unrelated Chinese patients (PA-1: c.649_650insC and c.707A > G; PA2: c.98C > T and c.707A > G; PA3: c.407G > A and c.650delTinsCTAA; PA4: c.1247G > T (homozygous); PA5: c.406C > T and c.1178A > G; NM_000478.5) were found. These variations caused two types of HPP: perinatal HPP and Odonto HPP. All cases reported in this study were autosomal recessive. Among the variants, c.1247G > T/p.Gly416Val (PA-4); c.1178A > G/p.Asn393Ser (PA-5) and c.707A > G/p.Tyr236Cys (PA-1, PA-2) have never been reported before.

Conclusion: Clinical phenotypes of perinatal HPP (PA-1,PA-2,PA-3 and PA-4) include skeletal dysplasia, shorter long bones, bowing of long bones, tetraphocomelia, abnormal posturing and abnormal bone ossification. Odonto HPP (PA-5) only presents as dental abnormality with severe dental caries and decreased ALP activity. Our study extends the pool of ALPL variants in different populations.

Intractable Vomiting in an 11-Month-Old Boy With Trisomy 21: A Case Report on Abnormal Calcium/Calcinosis/Creatinine in Down Syndrome

Abnormal calcium/calcinosis/creatinine in Down syndrome (ABCD syndrome) is a very rare condition with no clear etiology. In this paper, we describe our clinical encounter with this disease. We report the case of an 11-month-old male infant with Down syndrome (DS) who presented to the hospital with intractable vomiting and decreased oral intake and urine output. The evaluation revealed an acute kidney injury (AKI) and hypercalcemia. Although his AKI improved with intravenous hydration, his hypercalcemia persisted. Extensive studies were notable for an elevated urinary excretion of calcium and bilateral medullary nephrocalcinosis seen on renal ultrasound (US). As a result, he was diagnosed with ABCD syndrome. Dietary calcium restriction was implemented. During his follow-up visit with a pediatric endocrinologist, his serum calcium was found to be normalized. To our knowledge, this is only the seventh case report on ABCD syndrome in the literature.

Predictive modeling of hypophosphatasia based on a case series of adult patients with persistent hypophosphatasemia

Approximately half of individuals with hypophosphatasemia (low levels of serum alkaline phosphatase) have hypophosphatasia, a rare genetic disease in which patients may have stress fractures, bone and joint pain, or premature tooth loss. We developed a predictive model based on specific biomarkers of this disease to better diagnose this condition.

INTRODUCTION

Hypophosphatasemia is a condition in which low levels of alkaline phosphatase (ALP) are detected in the serum. Some individuals presenting with this condition may have a rare genetic disease called hypophosphatasia (HPP), which involves mineralization of the bone and teeth. Lack of awareness of HPP and its nonspecific symptoms make this genetic disease difficult to diagnose. We developed a predictive model based on biomarkers of HPP such as ALP and pyridoxal 5'-phosphate (PLP), because clinical manifestations sometimes are not recognized as symptoms of HPP.

METHODS

We assessed 325,000 ALP results between 2010 and 2015 to identify individuals suspected of having HPP. We performed univariate and multivariate analyses to characterize the relationship between hypophosphatasemia and HPP. Using several machine learning algorithms, we developed several models based on biomarkers and compared their performance to determine the best model.

RESULTS

The final cohort included 45 patients who underwent a genetic test. Half (23 patients) showed a mutation of the ALPL gene that encodes the tissue-nonspecific ALP enzyme. ALP (odds ratio [OR] 0.61, 95% confidence interval [CI] 0.3-0.8, p = 0.01) and PLP (OR 1.06, 95% CI 1.01-1.15, p = 0.04) were the only variables significantly associated with the presence of HPP. Support vector machines and logistic regression were the machine learning algorithms that provided the best predictive models in terms of classification (area under the curve 0.936 and 0.844, respectively).

CONCLUSIONS

Given the high probability of a misdiagnosis, its nonspecific symptoms, and a lack of awareness of serum ALP levels, it is difficult to make a clinical diagnosis of HPP. Predictive models based on biomarkers are necessary to achieve a proper diagnosis. Our proposed machine learning approaches achieved reasonable performance compared to traditional statistical methods used in biomedicine, increasing the likelihood of properly diagnosing such a rare disease as HPP.

Prosthodontic Rehabilitation of a Patient with Hypophosphatasia Using Dental Implants: A Case Report with Seven Years Follow-Up

Hypophosphatasia is a rare metabolic inherited dento-osseous disorder. Although there is some available literature on various dental characteristics of hypophosphatasia patients, few reports focus on the effects of hypophosphatasia on the permanent dentition and prosthodontic rehabilitation, particularly in relation to the use of dental implants. This paper reports a case with hypophosphatasia and prosthodontic rehabilitation using dental implants with 7-year follow-up.

Dental effects of enzyme replacement therapy in case of childhood-type hypophosphatasia

Background

Hypophosphatasia (HPP), a skeletal disease characterized by hypomineralization of bone and teeth, is caused by an ALPL gene mutation that leads to low activity of the tissue non-specific alkaline phosphatase enzyme. Although enzyme replacement therapy (ERT) was recently introduced for affected patients, no known studies have been reported regarding its dental effects related to permanent teeth and jaw bones. In the present study, we examined the dental effects of ERT in a case of childhood-type hypophosphatasia, including panoramic radiography findings used to estimate the dental age of permanent teeth and mandibular bone density. Furthermore, the effects of that therapy on the periodontal condition of the patient were evaluated by comparing periodontal pocket depth before and after initiation.

Case presentation

An 11-year-1-month-old boy was referred to our clinic for consultation regarding oral management. Two primary incisors had spontaneously exfoliated at 1 year 8 months old and he had been diagnosed with childhood-type HPP at the age of 2 years 2 months. Obvious symptoms were localized in the dental region at the time of diagnosis, though later extended to other parts of the body such as bone pain. ERT was started at 11 years 7 months of age, after which bone pain disappeared, and motor functions and activities of daily living improved. We estimated dental age based on tooth development stage. The age gap between chronological and dental ages was expanded before treatment, and then showed a constant decrease after ERT initiation and finally disappeared. The index for mandibular bone density (mandibular cortical width / length from mesial buccal cusp to apex of first molar) was increased after ERT initiation. Furthermore, the periodontal condition for all teeth except those exfoliated was stable after starting therapy.

Conclusions

ERT resulted in improved tooth and mandibular bone mineralization, with notably good effects on teeth under formation. Acceleration of mineralization of roots associated with erupting teeth leads to stabilization of the periodontal condition. We concluded that ERT contributed to the improved dental condition seen in this patient.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01673-2.

Weighted Gene Coexpression Network Analysis to Construct Competitive Endogenous RNA Network in Chromogenic Renal Cell Carcinoma

Aim

This study is aimed at constructing the competing endogenous RNA (ceRNA) network in chromophobe renal cell carcinoma (ChRCC).

Methods

Clinical and RNA sequence profiles of patients with ChRCC, including messenger RNAs (mRNAs), microRNAs (miRNAs), and long noncoding RNAs (lncRNAs), were obtained from The Cancer Genome Atlas (TCGA) database. “edgeR” and “clusterProfiler” packages were utilized to obtain the expression matrices of differential RNAs (DERNAs) and to conduct gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses. Weighted gene coexpression network analysis (WGCNA) was performed to screen the highly related RNAs, and miRcode, StarBase, miRTarBase, miRDB, and TargetScan datasets were used to predict the connections between them. Univariate and multivariate Cox proportional hazards regressions were performed in turn to elucidate prognosis-related mRNAs in order to construct the ceRNA regulatory network.

Results

A total of 1628 DElncRNAs, 104 DEmiRNAs, and 2619 DEmRNAs were identified. WGCNA showed significant correlation in 1534 DElncRNAs, 98 DEmiRNAs, and 2543 DEmRNAs, which were related to ChRCC. Fourteen DEmiRNAs, 113 DElncRNAs, and 43 DEmRNAs were screened. Nine mRNAs (ALPL, ARHGAP29, CADM2, KIT, KLRD1, MYBL1, PSD3, SFRP1, and SLC7A11) significantly contributed to the overall survival (OS) of patients with ChRCC (P < 0.05). Furthermore, two mRNAs (CADM2 and SFRP1) appeared to be independent risk factors for ChRCC.

Conclusion

The findings revealed the molecular mechanism of ChRCC and potential therapeutic targets for the disease.

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.

Metabolic Bone Diseases in the Pediatric Population

Bone plays an important role in regulating mineral balance in response to physiologic needs. In addition, bone is subject to a continuous remodeling process to maintain healthy bone mass and growth. Metabolic bone diseases are a heterogeneous group of diseases caused by abnormalities of bone mass, mineral structure homeostasis, bone turnover, or bone growth. In pediatrics, several significant advances have been made in recent years in the diagnosis of metabolic bone diseases (e.g., osteogenesis imperfecta, hyperparathyroidism, rickets, renal osteodystrophy, pediatric osteoporosis, and osteopetrosis). Imaging is fundamental in the diagnosis of these pathologies.

Investigation of ALPL variant states and clinical outcomes: An analysis of adults and adolescents with hypophosphatasia treated with asfotase alfa

BACKGROUND

Hypophosphatasia (HPP), a rare metabolic disease, can be inherited in an autosomal recessive (biallelic) or an autosomal dominant (monoallelic) manner. Most of the severe, early-onset, frequently lethal HPP in infants is acquired through recessive inheritance; less severe, later-onset, typically nonlethal HPP phenotypes are acquired through either dominant or recessive inheritance. HPP's variable clinical presentation arises from >400 identified ALPL pathogenic variants with likely variable penetrance, especially with autosomal dominant inheritance. This post hoc analysis investigated the relationship between ALPL variant state (biallelic and monoallelic) and clinical outcomes with asfotase alfa in HPP.

METHODS

Data were pooled from two phase 2, randomized, open-label studies in adolescents and adults with HPP; one study evaluated the efficacy and safety of different doses of asfotase alfa (n = 25), and the other assessed the pharmacodynamics and safety of asfotase alfa (n = 19). Patients were grouped by ALPL variant state (biallelic or monoallelic). Available data from both studies included ALPL pathogenic variant state, Baseline characteristics, HPP-specific medical history, and Baseline TNSALP substrate levels (inorganic pyrophosphate [PPi] and pyridoxal 5'-phosphate [PLP]) concentrations). Clinical outcomes over 5 years of treatment were available from only the efficacy and safety study.

RESULTS

In total, 44 patients with known variant status were included in the pooled analysis (biallelic, n = 30; monoallelic, n = 14). The most common pathogenic variant was c.571G > A (p.Glu191Lys) in biallelic patients (allele frequency: 19/60) and c.1133A > T (p.Asp378Val) in monoallelic patients (allele frequency: 7/28). Median (min, max) Baseline PPi concentrations were significantly higher in patients with a biallelic vs monoallelic variant state (5.3 [2.2, 12.1] vs 4.3 [3.5, 7.4] μM; P = 0.0113), as were Baseline PLP concentrations (221.4 [62.4, 1590.0] vs 75.1 [28.8, 577.0] ng/mL; P= 0.0022). HPP-specific medical history was generally similar between biallelic and monoallelic patients in terms of incidence and type of manifestations; notable exceptions included fractures, which were more common among monoallelic patients, and delayed walking and bone deformities such as abnormally shaped chest and head and bowing of arms or legs, which were more common among biallelic patients. Data from the efficacy and safety study (n = 19) showed that median PPi and PLP concentrations were normalized over 5 years of treatment in patients with both variant states. Median % predicted distance walked on the 6-Minute Walk Test remained within the normal range for monoallelic patients over 4 years of treatment, and improved from below normal (<84%) to normal in biallelic patients.

CONCLUSIONS

Although patients with biallelic variants had significantly higher Baseline PPi and PLP levels than monoallelic variants, both groups generally showed similar pretreatment Baseline clinical characteristics. Treatment with asfotase alfa for up to 5 years normalized TNSALP substrate concentrations and improved functional outcomes, with no clear differences between biallelic and monoallelic variant states. This study suggests that patients with HPP have significant disease burden, regardless of ALPL variant state.

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.

Clinical and genetic characteristics of hypophosphatasia in Chinese children

BACKGROUND

Hypophosphatasia (HPP) is a rare inherited disorder, which is caused by loss-of-function mutations in the ALPL gene. HPP is a heterogeneous disease that has a wide spectrum of phenotypes. Few studies were carried out in the Chinese population with HPP, especially in children.

METHODS

The clinical and genetic characteristics of 10 Chinese children with HPP who were referred to the Beijing Children's Hospital were described. Previously reported HPP cases of children in China were also reviewed.

RESULTS

A total of 33 cases were identified, which included 2 perinatal lethal HPP, 10 infantile HPP, 10 childhood HPP, and 11 odonto HPP. The male-to-female ratio was 24:9. The average age at onset was 0.69 years (ranged from 2 h after birth to 14 years), while the average age at clinical diagnosis was 3.87 years (ranged from 2 h after birth to 19 years). Serum alkaline phosphatase (ALP) levels were significantly decreased in patients with perinatal lethal/infantile HPP when compared with those with the mild forms of HPP childhood/odonto HPP (P < 0.01). Although serum phosphate levels were not different (P > 0.05), serum calcium levels were elevated, and serum intact parathyroid hormone levels were decreased in patients with perinatal lethal/infantile HPP in comparison with those with the childhood/odonto HPP (P all < 0.01). Genetic analyses identified 40 mutations in 31 HPP cases, including 28 missense mutations, 9 frameshift mutations, 2 splice junction alterations, and 1 regulatory mutation. Of which, 5 novel mutations were identified in our present study: 2 frameshift mutations (p.Arg138GlyfsTer27, p.Leu511Profs*272); 2 missense mutations (p.Ala176Val, p.Phe268Leu), and 1 splice junction alteration (c.297+5G>A). Compound heterozygous mutations accounted for 80.6% of all variants. No mutational "hot-spot" was found. Most mutations of ALPL were located in exons 5, 7, 10, and 3. Notably, subjects that carrying single heterozygous mutations showed milder phenotypes of HPP, while subjects with nonsense mutations were associated with a severer phenotype.

CONCLUSIONS

HPP is a rare disease with often delayed diagnosis, and the incidence of HPP in China may be seriously underestimated. The present study expands the phenotypic and genotypic spectrum and the understanding of HPP in Chinese children. These findings will be useful for clinical assessment and shorten the diagnosis time for pediatric HPP in China.

Hypophosphatasia: A Case of Two Patients With Spinal Cord Compression From Increase in Ligamentous Ossifications During Treatment

Treatment with asfotase alfa has transformed the prognosis of hypophosphatasia in children and improves the bone and muscle signs in adults. The doses used in adults are the same as in children, whereas bone remodeling is different between them. We report on the cases of two patients treated with 1 mg/kg/day of asfotase alfa who developed spinal cord compression from spinal ossifications during treatment. The first patient, 50 years old, presented after 2 years of treatment with quadraparesis secondary to an increase in ossifications of the cervical vertebral ligaments. The neurological damage was resolved after laminectomy, and the patient was then treated for 18 months with doses of 80 mg per week, without recurrence of the bone and muscle signs. The second patient, 26 years old, 78 kg, developed pain and cervical stiffness with pyramidal tract irritation secondary to ossifications of the vertebral ligaments. This improved with a reduction of doses to 80 mg/week, which then, after 6 months of follow‐up, enabled maintained improvement of the bone and muscle pain that was initially obtained. To our knowledge, these are the first reported cases of increased spinal ligamentous ossifications with neurological complications. Biological monitoring in adults does not seem to enable asfotase alfa doses to be adjusted. The levels of serum alkaline phosphatase (ALP) while on the recommended treatment of 1 mg/kg/day are significantly supraphysiological (5000 to 20,000 IU) and the assays of pyrophosphate and pyridoxal phosphate are not correlated with clinical efficacy. In both of our patients, the treatment with 80 mg of asfotase alfa per week, which was proposed after the occurrence of spinal complications, seemed as effective, after a follow‐up of 18 months and 6 months, as the initial treatment for improving the bone and muscle signs, and could be provided as “attack” doses after healing of the pseudoarthroses. © 2021 American Society for Bone and Mineral Research © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

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.