Comparison of serum catalytic activity and immunoreactivity of bone alkaline phosphatase in hypophosphatasia

Hypophosphatasia is a rare bone disorder characterised by low levels of tis sue non-specific alkaline phosphatase (TNSALP). Although TNSALP is widespre ad in virtually all tissues the clinical effects, when produced, seem only to affect the mineralizing tissue such as teeth and skeleton. The skeleton is severely affected in the perinatal form of the disease, when death may o ccur in utero, or may not be affected in the adult type variety of the dise ase. We therefore compared the catalytic (cBALP) and immunoreactivity (iBAL P) of bone alkaline phosphatase isoenzyme in six families with hypophosphat asia. iBALP was measured using an IRMA method. cBALP was measured after ele ctrophoretic separation of serum alkaline phosphatase isoenzymes on lectin containing agarose gel. The percentage of different isoenzymes was calculat ed using densitometric scanning and cBALP calculated from the known total s erum alkaline phosphatase activity. Results showed cBALP=0.796 + 3.269iBALP , r=0.9 p <0.01, in cases of hypophosphatasia. In general, the lower the iB ALP and cBALP the more severe the skeletal disease. The bone isoenzyme leve l predicts the clinical severity of bone disease. (C) 2000 Elsevier Science B.V. All rights reserved.