MELAS syndrome withmitochondrial tRNALeu(uuR) gene mutation ina Chinese family

Theclinical features ofa patient ina Chinesefamilywith mitochondrial myopathy, encephalopathy, lactic acidosis,and stroke-like episodes (MELAS syndrome)are reported. The study revealed thathearing andvisual impairmentsand miscarriages may be early clinical presentations inMELAS. A heteroplasmic A to G transition in the tRNAIAu(uuR) gene was notedat the nucleotide pair3243inthemitochondrial DNA ofmuscle, blood, andhairfollicles oftheprobandandhismaternal relatives.Quantitative analysisof the mutatedmitochondrial DNA revealed variable proportions indifferent tissues andsubjects ofmaternallineage inthe family. Muscletissue contained ahigher proportion ofthemutantmitochondria thanothertissues examined. Thefunctionofthereproductive systemofthe probandseemstobeimpaired. Inone clinically healthy sibling, the3243rd point mutation wasfoundinspermmitochondrial DNA,although spermmotility was notaffected. Itseemsthatbiochemical defects inmitochondrial respiration and oxidative phosphorylation aretissue specificexpressions ofthe3243rdpoint mutationinthemitochondrial DNA of theaffected target tissues.