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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., (© 2023. The Japanese Society Bone and Mineral Research.)

Introduction: Hypophosphatasia (HPP) is caused by mutations in the ALPL gene encoding tissue nonspecific alkaline phosphatase (TNSALP) and inherited in either an autosomal recessive or autosomal dominant manner. It is characterized clinically by defective mineralization of bone, dental problems, and low serum ALP levels. In the current report, we demonstrate a novel mutation in the ALPL gene (c.244G > A p.Gly82Arg) in a Japanese family with low serum ALP levels., Materials and Methods: The ALPL gene analysis using hybridization capture-based next-generation sequencing was performed. The expression plasmids of the wild type and mutated TNSALP were introduced into COS-7 cells. The enzymatic activity of ALP in the cell lysates was measured using p-nitrophenylphosphate as a substrate., Results: TNSALP with the novel ALPL mutation (c.244G > A p.Gly82Arg) completely lost its enzymatic activity and suppressed that of wild-type TNSALP, corroborating its dominant negative effect. The diagnosis of autosomal dominant HPP was confirmed in three members of the family., Conclusion: Our approach would help to avoid the inappropriate use of bone resorption inhibitors for currently mis- or under-diagnosed HPP, given that the presence of further, yet undetected mutations of the ALPL gene are plausible., (© 2021. The Japanese Society Bone and Mineral Research.)

Introduction: Hypophosphatasia (HPP) is caused by mutations in the ALPL that encodes the tissue-nonspecific isoenzyme of alkaline phosphatase (ALP). Clinical manifestations range from extreme life-threatening lethal forms to no signs or symptoms at all., Materials and Methods: Consecutive 30,000 outpatients and inpatients with ALP data were screened retrospectively, out of which 1000 patients were found to have low levels of ALP more than once. Then, patients were evaluated for the symptoms and signs of HPP with further biochemical and genetic analyses., Results: Thirty-seven patients who had severe musculoskeletal pain, recurrent fractures, and tooth anomalies were then screened with substrate and DNA sequencing analyses for HPP. It was determined that eight patients had variants in the ALPL gene. A total of eight different ALPL variants were identified in eight patients. The variants, namely c.244G > C (p.Gly82Arg), c.1444C > T (p.His482Tyr), c.1487A > G (p.Asn493Ser), and c.675_676insCA (p.Met226GlnfsTer52), had not been previously reported., Discussion: Considering the wide spectrum of clinical signs and symptoms, HPP should be among the differential lists of bone, muscle, and tooth abnormalities at any age.

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

Hypophosphatasia is a rare inherited disorder characterized by a low serum alkaline phosphatase (ALP) activity and defective bone mineralization. Adult hypophosphatasia typically manifests in middle-age as a result of osteomalacia with recurrent stress fractures of the lower limb. However, considerable variation occurs in the clinical expression of hypophosphatasia, and no curative treatment has yet been established. We herein report a case of adult hypophosphatasia with painful calcific periarthritis, which showed improvement after surgical resection. A 32-year-old male was referred to our clinic complaining of pain in his elbows and knees. A painful subcutaneous mass was palpable on his right lateral epicondyle, where periarticular calcification was detected by plain radiography. The laboratory data showed a slight decrease in serum ALP activity and bone mineral density, and an elevation in the urinary phosphoethanolamine. Genomic DNA sequencing revealed an F310L mutation and a Y246H polymorphism in the tissue-nonspecific alkaline phosphatase gene, confirming the diagnosis of hypophosphatasia. The pain in the patient's right elbow was not responsive to nonsteroidal anti-inflammatory drugs, and triamcinolone diacetate was locally injected for treatment. His symptoms were ameliorated after the injection; however, they recurred in 3 months, and he became refractory to additional steroid injection. Surgical debridement of the calcified lesion was performed, and his symptoms were successfully ameliorated after the surgery.

Hypophosphatasia is a rare inherited disorder characterized by poor bone mineralization and deficiency of alkaline phosphatase activity. It is caused by mutations in the liver/bone/kidney alkaline phosphatase gene encoding the tissue-nonspecific isoenzyme of alkaline phosphatase (TNAP), which displays many allelic heterogeneities, leading to different clinical phenotypes. This study reports the case of a patient diagnosed with lethal perinatal hypophosphatasia. His gene analysis showed compound heterozygocity of two novel mutations: c.650delTinsCTAA and c.984_986delCTT, which led to p.217delVinsAK and p.328delF, respectively. The two mutations originated separately from his parents, consistent with autosomal recessive perinatal hypophosphatasia. For these two novel mutations, we analyzed their functions through three-dimensional structural analysis. This revealed that V217 is located in the β-sheet area, V217 is deleted, and insertion of alanine and lysine alter the secondary structure, causing instability in the hydrophobic region, which may influence the metal-binding vicinity. This mutant structure loses its catalytic activity. Deletion of 328F also results in protein structural alteration and affects TNAP functions. These results may provide an explanation of the two novel mutated alleles correlating with the lethal phenotype of our patient. In conclusion, we demonstrated the case of a patient with lethal perinatal hypophosphatasia caused by two novel heterozygous mutations.

The tissue-nonspecific alkaline phosphatase (TNSALP) gene in four unrelated patients with hypophosphatasia was analyzed using polymerase chain reaction-single strand conformation polymorphism and the direct sequencing method. Of the participating patients, one had childhood-type and three had perinatal-type disease. All carried a deletion of T at cDNA number 1559, which causes a frameshift downstream from codon L503, as a heterozygote. In the childhood-type patient, an F310L mutation was detected in the opposite allele. Similarly, a perinatal-type patient carried a V3651 mutation in the opposite allele. Mutations in the opposite alleles were not detected in the other two patients with perinatal-type disease. In addition, although both parents carried the deletion as a heterozygote in two families with childhood-type and perinatal-type disease, patients from those families were not homozygous for the deletion. Several single-nucleotide polymorphisms (SNPs) were also detected, which were shown to be useful for haplotype analysis. Allele frequency of the deletion among Japanese patients was 36% (10 of 28 alleles) but none occurred in Caucasian patients. These findings indicate that regardless of clinical type, deletion in the TNSALP gene occurs frequently among Japanese patients. Furthermore, haplotype analysis using SNPs suggested that the deletion might have derived from more than a single founder.