Hypophosphatasia in Japan: ALPL Mutation Analysis in 98 Unrelated Patients
Hypophosphatasia (HPP) is highly variable in clinical expression and is generally classified into six subtypes. Although it would be beneficial to be able to predict the clinical course from the ALPL genotype, studies on this issue are limited. Here, we aimed to clarify the features of Japanese HPP and the relationships between genotype and clinical manifestations. We analyzed 98 unrelated Japanese patients to investigate the percentage of each clinical form, frequently detected mutations, and the relationship between the genotype and phenotype. Some of the identified mutants were characterized by transfection experiments. Perinatal severe form was the most frequent (45.9%), followed by perinatal benign form (22.4%). Among the 196 alleles, p.Leu520ArgfsX86 (c.1559delT) was detected in 89 alleles, and p.Phe327Leu (c.979T>C) was identified in 23 alleles. All of the homozygotes for p.Leu520ArgfsX86 were classified into perinatal severe form, and patients carrying p.Phe327Leu in one of the alleles were classified into perinatal benign or odonto HPP. Twenty of the 22 patients with perinatal benign HPP were compound heterozygous for p.Phe327Leu and another mutation. Most patients with odonto HPP were found to be monoallelic heterozygotes for dominant-negative mutations or compound heterozygotes with mutants having residual activity. The high prevalence of p.Leu520ArgfsX86 and p.Phe327Leu mutations might underlie the high rate of perinatal severe and perinatal benign forms, respectively, in Japanese HPP. Although ALPL genotyping would be beneficial for predicting the clinical course to an extent, the observed phenotypical variability among patients sharing the same genotypes suggests the presence of modifiers.
KeywordsHypophosphatasia Mutations Genotype–phenotype correlation ALPL
The authors thank all the patients, families, and doctors who contributed to this study. This work was supported by a grant from the Japan Agency for Medical Research and Development (AMED) Practical Research Project for Rare/Intractable Disease Project of Japan (17ek010935h0003), and by Research on rare and intractable diseases, Health, Labour and Welfare Sciences Research Grants (19FC1006).
Compliance with Ethical Standards
Conflict of interest
Toshimi Michigami, Kanako Tachikawa, Miwa Yamazaki, Masanobu Kawai, Takuo Kubota, and Keiichi Ozono declare that they have no conflict of interest.
Human and Animal Rights and Informed Consent
Informed consent was obtained from the patients or guardians of minor patients.
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