Isoenzymes of alkaline phosphatase in infantile hypophosphatasia.

Infantile hypophosphatasia is a rare inborn error of metabolism in which the expression of the liver/kidney/bone locus of the alkaline phosphatase gene is defective. Analysis of tissues from a suspected case of hypophosphatasia for alkaline phosphatase activity demonstrated very low levels of activity in liver, kidney, and rib as compared to tissues from a case of osteogenesis imperfecta or normal adult tissues. Intestinal and placental tissues demonstrated significant levels of activity. Gene-specific amino acid inhibitors and isoelectric focusing demonstrated that the activity which was present in the liver, kidney, and rib tissues from the case of hypophosphatasia was of the intestinal type and not the normal liver/kidney/bone form of the enzyme.