Early Age at Onset and High Frequency of Associated Complications in Maternally Transmitted Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a heterogeneous group of conditions characterized by hyperglycemia and shows different modes of inheritance (autosomal dominant, autosomal recessive and maternal inheritance). Inheritance pattern was studied in a total of 223 type 2 diabetic cases through the pedigree data obtained from the index cases. Of the total 223 cases studied, 159 cases showed familial incidence and the remaining cases had no family history of the disorder. The 159 cases, which had family history of diabetes, were analysed for mode of inheritance. 54 had female parent affected and 22 cases had male parent affected with disease thus suggesting that mothers are excessively impl icated in the transmission of the disorder. The 54 pedigrees where the female parent was affected were further analysed for the pattern of inheritance. It was observed that 23 (about 10% of the total cases studied) of them showed maternal mode of inheritance, wherein if the mother was affected with the disease, all the offspring’s (both male and female) are affected with the disease and only the affected daughters transmitted the condition to their progeny but the sons did not transmit the condition to their progeny. The remaining 31 pedigrees showed Mendelian mode of inheritance. Furthermore, cases showing maternal inheritance have an early age at onset of the disease compared to Mendelian mode of inheritance and are more frequently associated with the complications of the disorder (neuropathy, nephropathy, retinopathy, cardiovascular disorders). This study highlights the clinical importance of maternally inherited type 2 diabetes mellitus.