Intestinal Alkaline Phosphatase Activity in Familial Hypophosphatasia

Homogenates of small-Intestine mucosa obtained from members of a family with hypophosphatasia were assayed for alkaline phosphatase activity with four phosphate esters. The results were compared to those obtained for 14 control subjects. In one patient with clinical and biochemical manifestations of hypophosphatasia intestinal alkaline phosphatase activity for each substrate was either normal or elevated. Five relatives with only the biochemical abnormalities of the disease also had normal or elevated intestinal activities. Of two relatives with no apparent clinical or biochemical involvement, one had normal, and one had elevated intestinal alkaline phosphatase activities. The results show that, contrary to previous impressions, alkaline phosphatase activity is not uniformly reduced in all tissues in all patients with hypophosphatasia. These tissue differences may reflect differences in genetic control mechanisms.