The purpose of this study is to assess medical events during follow-up of adult patients having hypophosphatasia and consulting rheumatologists.

Hypophosphatasia (HPP) is a rare inherited disease caused by mutations of the ALPL gene. In adult HPP, patients may suffer from fractures, pseudofractures, fracture healing complications, osteoarthritis, chondrocalcinosis, dental diseases, muscle pain and disability, but also headache, muscle weakness, ocular disease, and other symptoms. In some cases the diagnosis is severely delayed. Moreover a number of patients having such symptoms and a low level of serum alkaline phosphatase, without gene mutation can be followed by rheumatologists with difficulties in management of bone fragility and pain. The aim of this register is to describe prospectively the medical events in adult patients having hypophosphatasia, whether or not there is a proven genetic abnormality.

Inclusion Criteria:

• men and women,
• aged 18 and over, with no upper age limit, who have had a total alkaline phosphatase value of less than 40 IU/l on at least 3 occasions, or at least a total alkaline phosphatase value below 40 IU/L and evidence of ALPL gene polymorphism
• with at least one rheumatological symptom.

Exclusion Criteria:

• transient hypophosphatasia: absence of confirmation of a value below 40 IU/l on at least 3 samples, lack of genetic confirmation
• secondary hypophosphatasia according to the expert rheumatologist (drugs, endocrine disease, other genetic disease...).

Patients with hypophosphatasia discovered in adulthood.