Large Islets, Beta-Cell Proliferation, and a Glucokinase Mutation

To the Editor: Rare, naturally occurring gene mutations provide important insights into normal human physiology. We report on a young girl with severe neonatal hypoglycemia due to a novel glucokinase mutation (V91L). Her father had a similar clinical course, but neither his DNA nor his pancreatic tissue was available for study. V91L showed a markedly increased affinity for glucose that was more than 8.5 times as high, an enzyme efficiency that was 7 times as high, and a relative-activity index that was 30 times as high as that of the wild-type enzyme. The estimated threshold for glucose-stimulated insulin secretion was . . .