Hypophosphatasia (HPP) is an inherited, chronic condition that affects the development of bones and teeth which can lead to devastating complications. It is caused by a defect in the gene that makes an enzyme called tissue-nonspecific alkaline phosphatase (TNSALP) leading to low alkaline phosphatase (ALP) activity which is necessary for bone formation and maintenance.
When ALP levels are low, this disrupts a process called mineralization, in which minerals such as calcium and phosphorus are deposited in developing bones and teeth. Mineralization is important in the development of strong bones. Therefore, in people with HPP, bones can be soft or weak leading to destruction and deformity of bones, skeletal abnormalities, and systemic complications including muscle weakness and respiratory failure.
Although HPP can occur anywhere from before birth to adulthood, the most severe forms of the disorder tend to occur before birth and in early infancy. Perinatal/infantile-onset is defined as symptoms appearing before 6 months of age and juvenile-onset is defined as symptoms appearing between 6 months and 18 years of age.