Persistent isolated hyperphosphatasemia.

We have presented the case of a 7-year-old girl with a two-year history of elevated levels of serum alkaline phosphatase, without evidence of bone or liver disease. Family investigations showed minimal increases in SAP levels in both of her parents. Eight other families with persistent isolated hyperphosphatasemia have been reported previously. This disorder differs from transient isolated hyperphosphatasemia by its later age of detection (usually greater than 5 years), duration of elevation (greater than 1 year), elevation of bone isoenzyme levels alone, and frequent familial incidence.