Alcaptonuria and sucrase-isomaltase deficiency in three offspring of a consanguineous marriage

Intestinal brush border membrane hydrolases and HLA lymphocyte antigens have been examined in three siblings with sucrose intolerance and alcaptonuria, and their consanguineous parents. Sucrase-isomaltase activity was absent in the three patients, and corresponded with the gel electrophoresis of SDS-solubilized brush border membranes, which failed to demonstrate the protein band normally associated with sucrase-isomaltase complex. The activities of all brush border membrane enzymes in the mother were normal, while those of the father were generally low. The use of hydrolytic capacity ratios, however, permitted the designation of both parents as heterozygotes. Significant homogentisic aciduria was found only in the three propositi, and no effect of homogentisic acid on the sucrase activities of two normal, unrelated children could be demonstrated in vitro. The HLA lymphocyte antigen profiles of all seven family members demonstrated remarkable histocompatibility in five of them.