Objective: HNF-1alpha gene mutations (MODY3) present with marked hyperglycemia in lean young adults and may, therefore, be mistaken for type 1 diabetes, with implications for individual treatment and risk of diabetes in other family members. We examined the prevalence of HNF-1alpha mutations in families with three generations of diabetes identified in a population-based study of childhood diabetes, representing a subpopulation in which misclassification was likely.
Research design and methods: In a study population of 1,470 families, 36 families (2.4%) with three affected generations were identified. In the 18 families in whom DNA samples were available, islet autoantibody testing, HLA class II genotyping, and HNF-1alpha sequencing were performed.
Results: At least one islet autoantibody was found in 13 of 14 probands, and diabetes-associated HLA class II haplotypes were found in 17 of 18. One proband, who had no islet autoantibodies and was homozygous for the protective HLA haplotype DRB1*02-DQB1*0602, had a novel HNF-1alpha heterozygous nonsense mutation (R54X). This mutation cosegregated with diabetes in the family. The proband, his brother, mother, and maternal grandmother were diagnosed with type 1 diabetes aged 14-18 years and treated with insulin (0.39-0.74 units/kg) from diagnosis. The mother has since been successfully transferred to sulfonylurea treatment.
Conclusions: Family history alone is of limited value in identification of individuals with HNF-1alpha mutations, and we propose a stepwise approach that restricts sequencing of the HNF-1alpha gene to those with a family history of diabetes who also test negative for islet autoantibodies.