A Retrospective Study of the Natural History of Patients With Severe Perinatal and Infantile Hypophosphatasia (HPP)

Inclusion Criteria: * Parent(s) or legal guardian(s) must provide written informed consent prior to data abstraction, unless all of the following apply: * The patient is deceased; AND * The responsible IRB/IEC/REB does not require informed consent per a review of their documented local policies for collecting retrospective data on patients who are deceased; AND * Written confirmation is received from the responsible IRB/IEC/REB confirming that the abstracted data can be analyzed and used to support regulatory filings by the Sponsor * Patient must have a documented diagnosis of HPP as indicated by 1 or more of the following: * Documented ALPL gene mutation(s) * Serum alkaline phosphatase (ALP) below the age-adjusted normal range and either plasma pyridoxal 5'-phosphate (PLP) or urinary phosphoethanolamine (PEA) above the upper limit of normal * Serum ALP below the age-adjusted normal range and HPP-related radiographic abnormalities on X-ray * Patient must have onset of signs of HPP prior to 6 months of age and have documentation of 1 or more of the following characteristics of perinatal and infantile HPP: * Respiratory compromise (up to and including respiratory failure) requiring institution of respiratory support measure(s), requiring medication(s) for management of symptom(s), and/or associated with other respiratory complications (e.g., pneumonia(s), respiratory tract infection(s)) * Pyridoxine (vitamin B6)-responsive seizures * Rachitic chest deformity Exclusion Criteria: Patients will be excluded from study participation if they have 1 or more of the following exclusion criteria: * Patient received treatment with asfotase alfa at any time prior to data abstraction * Patient has clinically significant other disease Both living and deceased patients will be considered for study participation