Aims/hypothesis. Maturity-onset diabetes of the young is an autosomal dominant form of diabetes characterised by an early age of onset (usually <25 years). We investigated the prevalence and trans-activating activity of hepatocyte nuclear factor (HNF)-1! mutations in southern Chinese families with MODY.

Methods. We screened for mutations in the HNF-1! gene in 50 unrelated southern Chinese families, which fulfilled the minimum criteria for MODY. Functional properties of the mutant proteins were investigated using site-directed mutagenesis and luciferase reporter assay.

Results. Five of the 50 (10%) families were found to have mutations in the coding region, including a new nonsense mutation Q176X and four reported mutations (frameshift mutation P379fsdelCT, nonsense mutation R171X, missense mutations G20R and P112L). These mutations had decreased trans-activating activity on the human insulin gene promoter. We also detected a new intronic sequence variation IVS7nt-6 GMA, which co-segregated with diabetes. The intronic variation creates a potential splice acceptor site and might alter the splicing of the HNF-1! mRNA.

Conclusion/interpretation. Mutations in the HNF-1! gene seem to be an important cause of MODY in southern Chinese. The mutations could affect normal islet function by altering the expression of target genes.