The Effect of Monoallelic Variants in the ALPL Gene on the Natural Course of Hypophosphatasia in Russia

Inclusion criteria: 1. Age ≥4 to \<18 years, or ≥18 years at the time of enrollment; 2. Signed ICF for patients ≥18 years, or legal representatives (parents) of patients aged ≥4 to \<18 years; 3. Written informed assent (for patients aged ≥14 to \<18 years only); 4. No history of HPP treatment with enzyme-replacement therapy; 5. Diagnosis of HPP confirmed by: * reduced alkaline phosphatase (ALP) activity relative to age- and sex-specific reference ranges, confirmed by at least two separate measurements, AND * the identification of a monoallelic pathogenic, likely pathogenic, or variant of uncertain significance in the ALPL gene on genetic testing. Exclusion Criteria: 1. Confirmed conditions presenting with clinical features overlapping with HPP, including but not limited to: cerebral palsy, Duchenne muscular dystrophy, limb-girdle muscular dystrophy (Erb-Roth dystrophy), acquired secondary myopathies of various etiologies; 2. Сurrent participation in any clinical study (patients participating in other non interventional studies may be included); 3. Homozygous or compound heterozygous mutation in the ALPL gene 4. In the opinion of the investigator, the patient is not able to return for follow-up visits or obtain required follow-up studies. 5. Pregnant and breastfeeding women.