Identification of new mutations in the hepatocyte nuclear factor 4alpha gene among families with early onset Type 2 diabetes mellitus.

Mutations in hepatocyte nuclear factor (HNF)-4alpha gene located on chromosome 20q have been found to be responsible for the development of early onset Type 2 diabetes mellitus (DM). Through a national campaign, 53 families with autosomal dominant, early onset Type 2 DM (n=654) were assembled to determine the frequency of mutations in the HNF-4alpha gene and their contribution to the development of diabetes. Twelve exons and the promoter region of the HNF-4alpha gene were screened in probands of the families by a double gradient, denaturing gradient gel electrophoresis (DG-DGGE) protocol combined with automated bi-directional sequencing of the PCR products of all heterozygous individuals. We detected two new mutations in the HNF-4alpha gene that changed the amino-acid sequence. The first mutation was a Gly-->Ser substitution in codon 115 within a highly conserved DNA binding domain, and all six carriers of this mutation had diabetes and low insulin secretion. The second mutation was an Ile-->Val substitution in codon 454 within the transactivation domain. It was carried by four family members, two of whom also carried a mutation in the HNF-1alpha gene. Of those having only the mutation in HNF-4alpha one had diabetes and the other had normal glucose tolerance and both were obese and hyperinsulinaemic. Thus, it is uncertain that this mutation is responsible for any of the diabetes in this family. We have found that mutations in the HNF-4alpha gene account for a small proportion, about 2-4%, of families with early onset, autosomal dominant, Type 2 DM in US Caucasians.