Alkaline phosphatase isoenzymes and clinical features in hypophosphatasia

Hypophosphatasia is an hereditary disease characterized by low activity of total serum alkaline phosphatase (TALP) accompanied by a range of skeletal diseases. We have measured the main circulating alkaline phosphatase isoenzymes--bone (BALP), liver (LALP), intestinal (IALP), placental (PALP)--in six families with hypophosphatasia, using kinetic and electrophorectic methods. Our observations show that patients with skeletal disease tend to have a very low BALP activity. Patients even with undetectable LALP activity do not appear to manifest any clinical complications. Patients also showed proportionately high IALP activity. Since the production of significant IALP activity is not a constant feature in all healthy individuals, it remains to be established whether the survival of one of these patients (IALP > 80% of TALP) depended on the presence of circulating IALP.