Abstract： Objective To investigate clinical traits of 2 families members habouring mtDNA 12026A→G mutation based on our previous studies.Methods 25 members in 2 families with probands with mtDNA 12026 mutation were examined.All their clinical and biochemical data were collected.Total genome was extracted conventionally from peripheral leucocytes of all participants,and PCR-RFLP techniques were applied to screen A to G substitution at nucleotide 12026 of mtDNA in ND4 region.Results We found 13 individuals habouring the 12026 A→G mutation in 2 pedigrees,all without deafness.Among them,5 with diabetes were found.Interestingly,we found 3 individuals with hyperthyroidism in one family(one also combined with diabetes).Conclusions Our findings suggest that diabetic families with mtDNA 12026 A→G mutation in ND4 region can have different clinical pictures,and may involve in autoimmune diseases