Analysis of mitochondrial DNA A3 243G point mutation in 9 cases with mitochondrial encephalomyopathy,lactic acidosis and stroke-like episodes

Objective To study the characteristics of molecular genetics concerning Chinese mitochondr ial encephalomyopathy,lactic acidosis and stroke-like episodes (MELAS). Methods A3243G and T3271C point mutations in the mtDNA of muscle and (or) blood cells were investigated in 9 patients with MELAS and some o f their maternal relatives from 7 families by using PCR-RFLP. Furthermore,mut ant mtDNA in the sample harboring mutation was quantitatively analysed. Results The mtDN A A3243G point mutation was unanimously identified in tissues of all patients an d 1 of their relatives. However,the T3271C point mutation was identi f ied in none of series in our study. The proportion of mtDNA A3243G was 46.8%～ 61. 0% in muscle (4 cases) as well as 26.8%～50.3% in blood (9 cases). In the 3 p atie nts with muscles and blood cells available,their mutant mtDNA proportion in mus cle is consistently higher than in blood cells. The study of leukocytes of some maternal relatives from 6 families showed that,while only 1 proband had a siste r harboring A3243G mutation and none of the mothers of another 3 probands or sib lings of the other 2 probands had the point mutation. However,the sons of 2 pr o bands had not only phenotype of MELAS,but also mtDNA A3243G point mutation in t heir blood. Conclusion mtDNA A3243G mutation highly exists in the series with M E LAS syndrome in our study and can be detected in various tissues,which is consi stent with reports abroad. However,most of our cases are sporadic rather than m aternal inherited. It is presumedly caused by a de novo mutation. Whether i t is due to ethnic difference or sporadic event needs to be investigated further.