Analysis of a non-functional HNF-1alpha (TCF1) mutation in Japanese subjects with familial type 1 diabetes

Mutations in the transcription factor hepatocyte nuclear factor-1alpha (HNF-1alpha; gene symbol TCF1) cause maturity-onset diabetes of the young type 3 (MODY3), a form of diabetes mellitus characterized by autosomal dominant inheritance, early onset, and pancreatic beta-cell dysfunction. Recent genetic studies, however, also found mutations in patients diagnosed with idiopathic (non-autoimmune based) type 1 diabetes. We identified a novel frameshift mutation (142delG) in the TCF1 gene in a family with a strong family history of type 1 diabetes and examined the functional properties of the mutant HNF 1alpha. The expression of the mutant protein was not detected in COS-7 cells by Western blot analysis after transfection of the mutant cDNA. This is the first case of an unstable mutant HNF-1alpha protein. Reporter gene analysis indicated that the mutant HNF-1alpha had no transactivation activity in HeLa and MIN6 cells. Haploinsufficiency for HNF-1alpha may lead to severe forms of diabetes like type 1 diabetes.