High frequency of mutations in MODY and mitochondrial genes in Scandinavian patients with familial early-onset diabetes

Aims/hypothesis. To investigate the contribution of mutations in maturity-onset diabetes of the young (MODY) and mitochondrial genes to early-onset diabetes with a strong family history of diabetes in a cohort with a high prevalence of Type I (insulin-dependent) diabetes mellitus. Methods. Screening for sequence variants in the hepatocyte nuclear factor (HNF)-4 alpha (MODY1), glucokinase (MODY2), HNF-1 alpha (MODY3) genes and mitochondrial DNA was carried out in 115 Finnish and Swedish patients with early-onset (less than or equal to 40 years) diabetes using the single strand conformation polymorphism (SSCP) technique and direct sequencing. Allele frequencies were compared with 118 patients with onset of diabetes Type II (non-insulin-dependent) diabetes mellitus after the age of 40 and 92 non-diabetic control subjects without a family history of diabetes. Results. In total 52 sequence variants were found in the HNF-1 alpha, HNF-4 alpha and glucokinase genes, 12 of which were considered as MODY mutations. Three families had the A3243G mutation in the mitochondrial tRNA(Leu) gene, which resulted in an overall pre valence of these mutations of 13%. Conclusion/interpretation. Among 115 Scandinavian families, mutations in the HNF-1 alpha gene represented the most common cause of familial early-onset (less than or equal to 40 years) diabetes: MODY3 (5.2%) more than MODY2 (3.5%) more than MIDD (2.6%) more than MODY1 (1.7%).