Mitochondrial gene mutations in familial non-insulin-dependent diabetes mellitus in Taiwan

Mitochondrial gene mutations are found to cause certain forms of diabetes mellitus and related syndromes. To study the prevalence of mitochondrial gene mutations in subjects with non-insulin-dependent diabetes mellitus (NIDDM) in Taiwan, 23 pedigrees with multiple siblings affected with NIDDM were consecutively collected from patients living in northern Taiwan. The A-to-G mutation at position 3243 np in the tRNA Leu gene and the mutation at position 8344 were screened by PCR-RFLP methods and confirmed by direct DNA sequence analysis. Among 23 NIDDM pedigrees, one pedigree was found to carry the 3243 np mutation. There was no 8344 np mutation in this series. Clinical features of this pedigree were consistent with mitochondrial disease in terms of maternal transmission, relatively early onset, non-obesity, insulin-requirement and association with hearing impairment. There was no correlation between the degree of heteroplasmy of mitochondrial gene mutation in leukocyte DNA and clinical severity. We conclude that a mitochondrial gene defect is an important genetic factor in familial cases with NIDDM in Taiwan.