Clarify HPP: Disease Burden of HPP Patients in China

Inclusion Criteria: Participants are eligible to be included in the study only if all the following criteria apply: 1. Confirmed diagnosis of HPP, defined by meeting all the following: * At least 1 skeletal or non-skeletal manifestation consistent with HPP; * Persistently low age- and sex-adjusted ALP: at least two independent tests with an interval of ≥14 days, both results below the local laboratory's age-/sex-specific reference lower limit; * Positive ALPL gene test result (pathogenic or likely pathogenic variant, or variant of uncertain significance \[VUS\]) - gene testing will be provided by the study if not already available for the participant; OR Elevated pyridoxal 5'-phosphate (PLP) level, if this test is available at the clinic. 2. Participant or parent (or legal guardian) must provide written informed consent prior to the performance of any study-related procedures and must be willing to comply with study procedures. Exclusion Criteria: Participants will be excluded from the study if they meet any of the following criteria: 1. Prior or current use of first-generation asfotase alfa at any time before study enrollment. 2. Participation in any other interventional clinical trial for HPP or other metabolic diseases within 3 months prior to study enrollment. 3. Severe comorbid conditions (e.g., end-stage organ failure, advanced malignancy) judged by the treating physician to interfere with the collection of valid study data or participant safety during follow-up. 4. Inability to comply with study follow-up procedures (e.g., geographic inaccessibility, cognitive impairment) as assessed by the treating physician.