Three mutant insulins in man.

We have previously identified a structurally abnormal insulin in the serum and pancreas of a middle-aged man with diabetes mellitus which arose from a leucine for phenylalanine substitution at position 24 or 25 of the insulin B chain; further analysis of the patient's leukocyte DNA showed that one of the patient's insulin alleles had undergone mutation resulting in loss of an MboII restriction site normally present in the human insulin gene. Two additional and unrelated patients with the same clinical syndrome have now been identified (ref. 4 and unpublished results). All of these patients showed hyperglycaemia typical of diabetes and with marked hyperinsulinaemia typical of insulin resistance, but all three show normal tolerance to exogenously administered insulin. As the opportunity of examining pancreatic tissue from patients suspected of secreting insulin variants is rare, we have developed a method combining HPLC and radioimmunoassay to identify insulin variants isolated from human sera. By this method we have shown that all three patients noted above secrete structurally variant and chemically distinct insulins. In correction of our original assignment, one is identified as [LeuB25]insulin.