Analysis of the HNF4 alpha gene in Caucasian Type II diabetic nephropathicpatients

Aims/hypothesis. Linkage and association studies in Caucasian patients with Type II (non-insulin-dependent) diabetes mellitus suggest that one or more diabetes susceptibility gene(s) reside within human chromosome 20q12-13.1. This region of chromosome 20 contains the maturity-onset diabetes of the y oung type 1 gene, HNF4 alpha. The purpose of this study was to assess the p ossible involvement of HNF4 alpha in Type II diabetes. Methods. Mutation analysis was done on the 12 exons and promoter regions of the HNF4 alpha gene in 182 Caucasian diabetic nephropathic patients and 10 0 Caucasian control subjects. The functional consequences of a novel promot er mutation were examined using a reporter system in the HepG2 liver cell L ine and electrophoretic mobility shift assays. Results. We identified two novel mutations in the HNF4 alpha, an R323H miss ense mutation in exon 8, and a 7 bp deletion (Delta 7) in the proximal prom oter region resulting in deletion of a single putative Spl binding site. Us ing a reporter assay system, the Delta 7 sequence was found to exhibit a 51 .2% (standard error +/- 4.2 %) reduction in promoter activity relative to t he normal sequence. In electrophoretic mobility shift assays using specific and non-specific competitors, the Delta 7 sequence had a 45.5% (range 40.4 -46.6) reduction in binding compared with the normal sequence. The Delta 7 allele occurs in a family with multiple cases of Type II diabetes in a patt ern consistent with coinheritance of the Delta 7 allele and diabetes. Conclusion/interpretation. Analysis of the HNF4 alpha gene revealed two pos sible mutations in 182 diabetic patients which suggests that the HNF4 alpha gene does not make a large contribution to diabetes susceptibility in the general population of Caucasian diabetic nephropathic patients. Functional analysis of the Delta 7 promoter deletion suggests, however, that promoter mutations in otherwise normal genes could contribute to diabetes susceptibi lity.