Mitochondrial DNA mutation at np 3243 in a family with maternally inherited diabetes mellitus

Mitochondrial DNA (mtDNA) gene defects may play a role in the development o f maternally inherited diabetes mellitus and deafness (MIDD). A family from Southern Italy who showed maternal transmission of type 2 diabetes mellitu s with three individuals affected is described. A 10.4 kb deletion and muta tions at nucleotide positions (np) 3243, 7445 and 11778 in the mtDNA of six relatives were sought. The mitochondrial np 3243 mutation of the tRNA Leu (UUR) gene was identified in a boy affected by optic atrophy and mental ret ardation, as well as in his diabetic mother. No other mutations or deletion s were found, Our study points out the variable phenotypic expression of th e np 3243 mtDNA mutation. This may suggest the presence of other mitochondr ial or nuclear mutations required to modulate the phenotype. A clinical and metabolic follow-up of all family members was necessary to understand the role of the np 3243 mutation, especially in one child affected by optic atr ophy and mental retardation. Further studies will be aimed at investigating the prevalence of mutations and deletions of mtDNA in type 2 diabetes mell itus.