Molecular epidemiologic study of mitochondrial DNA mutations in patients with mitochondrial diseases in Taiwan

We report an 8-year molecular study of mitochondrial DNA (mtDNA) mutations in patients with mitochondrial diseases in Taiwan. One hundred and seventy- seven patients met the diagnostic criteria of mitochondrial disease and wer e recruited into the study. The results showed that 32 patients, including 25 with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like e pisodes (MELAS) syndrome, one with Kearns-Sayre syndrome (KSS), one with di abetes mellitus and deafness, and five with chronic progressive external op hthalmoplegia (CPEO), harbored the A3243G mtDNA mutation. The A8344G mutati on was found in nine patients, all of whom suffered from myoclonic epilepsy and ragged-red fibers (MERRF) syndrome. The G11778A mtDNA mutation was fou nd in 18 of 22 patients with Leber's hereditary optic neuropathy. The T8993 C and T8993G mutations were found, respectively, in one and two patients wi th Leigh syndrome. Large-scale deletions of mtDNA were found in 17 patients with CPEO, one with KSS, one with MELAS, and two with MERRF syndrome. The mtDNA mutations in patients with each of the mitochondrial diseases found i n Taiwan were restricted mainly to a single site, while those reported for the same diseases in other ethnic groups occurred in many sites. Furthermor e, significant levels of additional mtDNA mutations occurred in some patien ts with mitochondrial encephalomyopathies We suggest that these additional (or secondary) mtDNA mutations are generated as a consequence of the preexi sting primary mtDNA mutations and may contribute to the age-dependent progr essive deterioration characteristic of mitochondrial diseases.