This study aims to characterize the natural history of patients with severe perinatal or infantile onset HPP.

Hypophosphatasia (HPP) is a life-threatening, genetic, and ultra-rare metabolic disease characterized by defective bone mineralization and impaired phosphate and calcium regulation that can lead to progressive damage to multiple vital organs, including destruction and deformity of bones, profound muscle weakness, seizures, impaired renal function, and respiratory failure. There are no approved disease-modifying treatments for patients with this disease. There is also limited data available on the natural course of this disease over time, particularly in patients with the juvenile-onset form.

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

Patients with perinatal and/or infantile onset HPP. Thirty-six patients were invasively ventilated or died, and 12 patients were censored.

Participation in a multicenter study involves a commitment to publish the data from the study in a cooperative publication prior to release of study results on an individual basis. Therefore, PIs are subject to certain disclosure and publication limitations.