Development of a functional beige fat cell line uncovers independent subclasses of cells expressing UCP1 and the futile creatine cycle.

Although uncoupling protein 1 (UCP1) is established as a major contributor to adipose thermogenesis, recent data have illustrated an important role for alternative pathways, particularly the futile creatine cycle (FCC). How these pathways co-exist in cells and tissues has not been explored. Beige cell adipogenesis occurs in vivo but has been difficult to model in vitro; here, we describe the development of a murine beige cell line that executes a robust respiratory response, including uncoupled respiration and the FCC. The key FCC enzyme, tissue-nonspecific alkaline phosphatase (TNAP), is localized almost exclusively to mitochondria in these cells. Surprisingly, single-cell cloning from this cell line shows that cells with the highest levels of UCP1 express little TNAP, and cells with the highest expression of TNAP express little UCP1. Immunofluorescence analysis of subcutaneous fat from cold-exposed mice confirms that the highest levels of these critical thermogenic components are expressed in distinct fat cell populations.

Hypoalkaline Phosphatemia Dental Type: A Case Report.

Mutations in dental hypophosphatasia (HPP) have been reported less than those in other types of HPP because the symptoms are mild or the dental lesions are only partial manifestations of other types of HPP. In this case, we observe the clinical manifestation of dental hypoalkaline phosphatase by analyzing the genetic mutation and biochemical parameters in child. The clinical data of the child with odonto HPP were collected and analyzed. The blood samples of the child and his parents were sequenced and verified using Sanger through a specific probe capture and high-throughput second-generation sequencing technology. Major clinical manifestations in the patient were early loss of deciduous teeth, significantly lower serum alkaline phosphatase (ALP) levels, lower active vitamin D, and increased blood phosphorus, but no abnormality was observed in the oral X-ray. Two missense mutations-c.542C>T (p. ser181leu) and c.644 T> C (p.Ile215Thr)-were found in exon 6 of the ALPL gene from the father and mother, respectively. The clinical manifestations of odonto hypophosphatasia were early loss of deciduous teeth and significantly reduced serum ALP levels. Of 2 mutations-c.542C>T (p.ser181leu) and c.644 T> C (p.Ile215Thr)-in the ALPL gene, c.644 T> C (p.Ile215Thr) was a new mutation.

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.

Pediatric hypophosphatasia: avoid diagnosis missteps!

Hypophosphatasia (HPP) is the dento-osseous disorder caused by deactivating mutation(s) of ALPL, the gene that encodes the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP). In HPP, 3 natural substrates of cell-surface TNSALP accumulate extracellularly; phosphoethanolamine (PEA), inorganic pyrophosphate (PPi), and pyridoxal 5'-phosphate (PLP). Hypophosphatasemia together with elevated plasma levels of PEA, PPi, and PLP comprise its biochemical signature. PPi can inhibit mineralization and in extracellular excess can impair bone and tooth hardening and perhaps explain weak muscle. Autosomal dominant or autosomal recessive inheritance from among more than 400 mutations of ALPL largely accounts for HPP's broad-ranging severity, greatest among all skeletal diseases. Pediatric HPP spans life-threatening perinatal and infantile forms, childhood forms, and odonto-HPP selectively featuring premature loss of deciduous teeth. ALPL gene testing and TNSALP supplementation therapy have bolstered familiarity with HPP, but there are new considerations for diagnosis. Herein, diagnosis of a boy's mild childhood HPP was delayed by missteps involving his medical and dental history, physical examination, radiographic findings, and clinical laboratory studies. We review how pediatric HPP is now identified. Prompt diagnosis while appreciating the broad-ranging severity of HPP underlies the safe and effective management of this inborn-error-of-metabolism.

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.

ALPL regulates pro-angiogenic capacity of mesenchymal stem cells through ATP-P2X7 axis controlled exosomes secretion.

BACKGROUND: Early-onset bone dysplasia is a common manifestation of hypophosphatasia (HPP), an autosomal inherited disease caused by ALPL mutation. ALPL ablation induces prototypical premature bone ageing characteristics, resulting in impaired osteogenic differentiation capacity of human bone marrow mesenchymal stem cells (hBMMSCs). As angiogenesis is tightly coupled with osteogenesis, it also plays a necessary role in sustaining bone homeostasis. We have previously observed a decrease in expression of angiogenesis marker gene CD31 in the metaphysis of long bone in Alpl+/- mice. However, the role of ALPL in regulation of angiogenesis in bone has remained largely unknown. METHODS: Exosomes derived from Normal and HPP hBMMSCs were isolated and identified by ultracentrifugation, transmission electron microscopy, and nanoparticle size measurement. The effects of ALPL on the angiogenic capacity of hBMMSCs from HPP patients were assessed by immunofluorescence, tube formation, wound healing and migration assay. exo-ELISA and Western Blot were used to evaluate the exosomes secretion of hBMMSCs from HPP, and the protein expression of VEGF, PDGFBB, Angiostatin and Endostatin in exosomes respectively. RESULTS: We verified that ALPL ablation resulted in impaired pro-angiogenic capacity of hBMMSCs, accounting for reduced migration and tube formation of human umbilical vein endothelial cells, as the quantities and proteins composition of exosomes varied with ALPL expression. Mechanistically, loss of function of ALPL enhanced ATP release. Additional ATP, in turn, led to markedly elevated level of ATP receptor P2X7, which consequently promoted exosomes secretion, resulting in a decreased capacity to promote angiogenesis. Conversely, inhibition of P2X7 increased the angiogenic induction capacity by preventing excessive release of anti-angiogenic exosomes in ALPL deficient-hBMMSCs. CONCLUSION: The ALPL-ATP axis regulates the pro-angiogenic ability of hBMMSCs by controlling exosomes secretion through the P2X7 receptor. Thus, P2X7 may be proved as an effective therapeutic target for accelerating neovascularization in ALPL-deficient bone defects.

A Case of Hypophosphatasia With Normal Alkaline Phosphatase Levels.

Background/Objective: Hypophosphatasia (HPP) is a rare disease associated with low serum alkaline phosphatase (ALP) activity. Here, we present a case of a patient with normal serum ALP levels diagnosed with HPP. Case Report: A 36-year-old woman presented with progressive fatigue, weakness, and joint pain. She had been evaluated in the past for genetic disorders due to these symptoms and was found to have a history of several total ALP levels within normal limits but elevated vitamin B6 levels. She also reported having loose teeth and "gray gums" during her childhood. Bone-specific ALP was tested for suspicion of HPP and returned at 4.4 µ/L (reference range, 5.3-19.5 µg/L), which prompted genetic testing. Genetic testing confirmed a positive pathogenetic variant of the ALPL gene, the c.542C>T (p.Ser181Leu) variant. She started asfotase alfa treatment to improve her symptoms. Discussion: HPP was diagnosed based on clinical suspicion supported by laboratory findings, which can cause it to be underdiagnosed or misdiagnosed. Current literature reports that a low total ALP level is the main biochemical marker of HPP and the only level needed to diagnose the disease. However, bone-specific ALP, a common marker used for bone turnover, has not been required to be tested. Conclusion: This case highlights a patient with normal total ALP, but low bone-specific ALP diagnosed with HPP confirmed by genetic testing. This case warrants future investigation into the diagnostic approach to HPP and the diagnostic utility between ALP and bone-specific ALP.

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.

TGF-ß1/Smad3 Signaling Is Required to Alleviate Fluoride-Induced Enamel Hypomineralization.

Excessive fluoride intake during enamel development can affect enamel mineralization, leading to dental fluorosis. However, its potential mechanisms remain largely unexplored. In the present study, we aimed to investigate the impact of fluoride on the expressions of RUNX2 and ALPL during mineralization and the effect of TGF-ß1 administration on fluoride treatment. A dental fluorosis model of newborn mice and an ameloblast cell line ALC were both used in the present study. The mice of the NaF group, including the mothers and newborns, were fed with water containing 150 ppm NaF after delivery to induce dental fluorosis. The mandibular incisors and molars showed significant abrasion in the NaF group. Immunostaining, qRT-PCR, and Western blotting analysis indicated that exposure to fluoride markedly down-regulated RUNX2 and ALPL in mouse ameloblasts and ALCs. Besides, fluoride treatment significantly decreased the mineralization level detected by ALP staining. Furthermore, exogenous TGF-ß1 up-regulated RUNX2 and ALPL and promoted mineralization, while the addition of SIS3 could block such TGF-ß1-induced up-regulation. In TGF-ß1 conditional knockout mice, the immunostaining of RUNX2 and ALPL was weaker compared with wild-type mice. Exposure to fluoride inhibited the expressions of TGF-ß1 and Smad3. Co-treatment of TGF-ß1 and fluoride up-regulated RUNX2 and ALPL compared with the fluoride alone treatment, promoting mineralization. Collectively, our data indicated that TGF-ß1/Smad3 signaling pathway was necessary for the regulatory effects of fluoride on RUNX2 and ALPL, and the fluoride-induced suppression of ameloblast mineralization was mitigated by activating TGF-ß1/Smad3 signaling pathway.

Proposed diagnostic criteria for the diagnosis of hypophosphatasia in children and adolescents: results from the HPP International Working Group.

Hypophosphatasia (HPP) is a rare inborn error of metabolism that presents variably in both age of onset and severity. HPP is caused by pathogenic variants in the ALPL gene, resulting in low activity of tissue nonspecific alkaline phosphatase (TNSALP). Patients with HPP tend have a similar pattern of elevation of natural substrates that can be used to aid in diagnosis. No formal diagnostic guidelines currently exist for the diagnosis of this condition in children, adolescents, or adults. The International HPP Working Group is a comprised of a multidisciplinary team of experts from Europe and North America who have expertise in the diagnosis and management of patients with HPP. This group reviewed 93 papers through a Medline, Medline In-Process, and Embase search for the terms "HPP" and "hypophosphatasia" between 2005 and 2020 and that explicitly address either the diagnosis of HPP in children, clinical manifestations of HPP in children, or both. Two reviewers independently evaluated each full-text publication for eligibility and studies were included if they were narrative reviews or case series/reports that concerned diagnosis of pediatric HPP or included clinical aspects of patients diagnosed with HPP. This review focused on 15 initial clinical manifestations that were selected by a group of clinical experts.The highest agreement in included literature was for pathogenic or likely pathogenic ALPL variant, elevation of natural substrates, and early loss of primary teeth. The highest prevalence was similar, including these same three parameters and including decreased bone mineral density. Additional parameters had less agreement and were less prevalent. These were organized into three major and six minor criteria, with diagnosis of HPP being made when two major or one major and two minor criteria are present.

A Novel Case of Concomitant PHEX and ALPL Mutation In a Family With Rickets.

Currently, no published cases report concomitant X-linked hypophosphatemia (XLH) and adult hypophosphatasia (HPP). Both diseases share clinical phenotypes that are almost indistinguishable. The correct diagnosis may be missed without a standardized laboratory and genetic testing approach. Pathogenic variants in the phosphate regulating endopeptidases homolog X-linked gene (PHEX) and the tissue-nonspecific alkaline phosphatase gene (ALPL) are genes that cause XLH and HPP, respectively. We describe a concomitant yet undescribed genetic pathogenic variant in a family. A 61-year-old woman was referred by orthopedic surgery for the presence of bilateral leg bowing and short stature during the assessment of knee surgery. The patient had a biochemical workup relevant for low serum phosphorus and 1,25-dihydroxy vitamin D and normal alkaline phosphatase (ALP). Genetic analysis revealed pathogenic variants in PHEX and ALPL. Her 42-year-old daughter shared identical symptoms and genetic variants with her mother. Both patients started conventional treatment for XLH with phosphorus and vitamin D, and the daughter later switched to burosumab-twza. Adult XLH and HPP may have similarities in clinical presentation but differ in some essential laboratory findings. Normal ALP levels helped direct our diagnosis toward XLH. However, the diagnosis was challenging due to the presence of concurrent variants in the genes involved. These variants illustrate the significant heterogeneity of the clinical expression.

Uncovering structural variants associated with body weight and obesity risk in labrador retrievers: a genome-wide study.

Although obesity in the domestic dog (Canis lupus familiaris) is known to decrease well-being and shorten lifespan, the genetic risk variants associated with canine obesity remain largely unknown. In our study, which focused on the obesity-prone Labrador Retriever breed, we conducted a genome-wide analysis to identify structural variants linked to body weight and obesity. Obesity status was based on a 5-point body condition score (BCS) and the obese dog group included all dogs with a BCS of 5, along with dogs with the highest body weight within the BCS 4 group. Data from whole-gene sequencing of fifty dogs, including 28 obese dogs, were bioinformatically analyzed to identify potential structural variants that varied in frequency between obese and healthy dogs. The seven most promising variants were further analyzed by droplet digital PCR in a group of 110 dogs, including 63 obese. Our statistical evidence suggests that common structural mutations in or near six genes, specifically ALPL, KCTD8, SGSM1, SLC12A6, RYR3, and VPS26C, may contribute to the variability observed in body weight and body condition scores among Labrador Retriever dogs. These findings emphasize the need for additional research to validate the associations and explore the specific functions of these genes in relation to canine obesity.

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.

Odontohypophosphatasia caused by a novel combination of two heterozygous variants: a case report.

Hypophosphatasia (HPP) is a rare genetic disorder mainly characterized by skeletal dysplasia that results from a deficiency in tissue-nonspecific alkaline phosphatase (TNSALP), which is encoded by the alkaline phosphatase (ALPL) gene. Odontohypophosphatasia (odonto-HPP) is a mild form of HPP characterized by oral symptoms, such as premature loss of primary teeth. This study was to describe a 4-year-old boy with premature loss of primary teeth who was diagnosed with odonto-HPP. X-ray radiography and laboratory examinations were performed for the diagnosis. Genetic etiology was revealed by whole-exome sequencing. A novel combination of two variants in the ALPL gene was identified in this case; this combination resulted in the odonto-HPP phenotype. c.346G>A (p.Ala116Thr) was inherited from the proband's father, whereas c.1563C>G (p.Ser521Arg) was inherited from the proband's mother. The proband's 8-year-old sister was a heterozygous carrier of c.346G>A (p.Ala116Thr) in the ALPL gene. Thus far, the proband's sister has been asymptomatic. Our findings indicate that c.346G>A is a pathogenic genetic alteration; c.1563C>G might cause a predisposition to the dental phenotype in combination with c.346G>A. It is important for pediatric dentists to consider a diagnosis of odonto-HPP in children with premature loss of primary teeth.

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 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.

Clinical and Genetic Characteristics of Hypophosphatasia in Chinese Adults.

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

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.

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.