Mitochondrial diseases are a clinically heterogeneous group of disorders that arise as a result of dysfunction of the mitochondrial respiratory chain. They can be caused by mutations in both nuclear and mitochondrial DNA. In fact, mitochondrial DNA (mtDNA) defects are known to be associated with a large spectrum of human diseases and patients might present wide range of clinical features with various combinations.

Our study reported a Tunisian family with clinical features of maternally inherited diabetes and deafness (MIDD). Accordingly, we performed a whole mitochondrial genome mutational analysis, results revealed a haplotype composed by “A750G, A1438G, G8860A, T12705, T14766C and T16519C”, in homoplasmic state, in the mother and transmitted to her daughter and her son. The patient with MIDD2 and retinopathy presented, in addition to this haplotype associated to the MIDD, two de novo variations including a novel one m.8241 T > G (p. F219C) in MT-CO2 gene and a known one m.13276G > A (p. M314 V) in MT-ND5 gene. The coexistence of these two mutations could explain the retinopathy observed in this patient.