Hereditary hypophosphatasia and hyperphosphatasia.

Hereditary hypophosphatasia and hyperphosphatasia are two rare skeletal disorders, which commonly present during childhood and are characterized by a decrease and an increase, respectively, in serum tissue nonspecific alkaline phosphatase activity. The primary defect in hereditary hypophosphatasia appears to be a structural abnormality in the tissue nonspecific alkaline phosphatase gene, resulting in a decrease or absence of enzymatic activity. The pathogenesis of hyperphosphatasia is unknown. There is no treatment for hypophosphatasia. Treatment with pamidronate appears promising for patients with hereditary hyperphosphatasia.