Inherited isolated hyperphosphatasemia.

An 11-year-old girl presented with permanent elevation of serum alkaline phosphatase activity (AP) exceeding 4 times the upper normal limit. Family investigations revealed a persistent increment of AP activity in the father and one of the two sisters, indicating a dominant form of inheritance. Physical examination and laboratory results were normal; isoenzyme studies revealed that the raised serum AP activity was mainly due to an increase of the bone isoenzyme. No disturbance of calcium or phosphate metabolism or morphological alterations of the skeleton could be demonstrated. This indicates an inherited abnormality in the metabolism of bone AP in the absence of disease.