Identification and functional analysis of mutations in the hepatocyte nuclear factor-1 alpha gene in anti-islet autoantibody-negative Japanese patients with type 1 diabetes

Mutations in the hepatocyte nuclear factor-1 alpha (HNF-1 alpha) gene are t he cause of maturity-onset diabetes of the young type 3 (MODY 3), which is characterized by a severe impairment of insulin secretion and early onset o f the disease. Although the majority of patients with type 1 diabetes have type 1A, immune-mediated diabetes, there is a significant percentage of the patients who have no evidence of an autoimmune disorder at the onset of di sease. The aim of this study was to estimate the prevalence of MODY 3 in an tiislet autoantibody negative patients with type 1 diabetes. From a large p opulation-based sample of unrelated Japanese patients with type 1 diabetes, 28 patients who lacked autoantibodies to glutamic acid decarboxylase, isle t cell antigen 512/insulinoma-associated antigen-2, phogrin (phosphate homo log of granules of insulinoma)/insulinoma-associated antigen-2 beta, and in sulin at the onset of type 1 diabetes were examined by PCR-based direct seq uencing of the 10 exons, flanking introns, and the promoter region of the H NF-1 alpha gene. Two (7.1%) of 28 autoantibody-negative patients with type 1 diabetes were identified as carrying mutations in the HNF-1 alpha gene. O ne patient carried a frameshift mutation (Pro(379)fsdelCT) in exon 6, and a nother patient carried a novel 2-bp substitution at nucleotides +45 (G to A ) and +46 (C to A) from the transcriptional site of the promoter region. Th ese mutations were identified in heterozygous form and were not identified in 64 unrelated healthy control subjects or 54 unrelated islet autoantibody -positive patients with type 1 diabetes. Functional analysis of the mutant HNF-1 alpha gene indicated that the Pro379fsdelCT mutation had no transcrip tional trans-activation activity and acted in a dominant negative manner. T he +45/46 GC to AA mutation in the promoter region showed reduced promoter activity by 10-20% compared to the wild-type sequence. In conclusion, about 7% of Japanese diabetic patients lacking antiislet autoantibodies initiall y classified as having type 1 diabetes could have diabetes caused by mutati ons in the HNF-1 alpha gene.