Higher proportion of mitochondrial A3243G mutation in blood than in skeletal muscle in a patient with cardiomyopathy and hearing loss

Phenotypes of individuals with the mitochondrial A3243G mutation and amount of mutant DNA in different tissues can be very variable, but the proportion of mutant DNA was consistantly lower in blood than muscle in previously studied patients. We detected the A3243G mutation in a 54-year-old patient with cardiomyopathy and hearing loss, where the amount of mutant DNA was higher in blood (19%) than in muscle (6%). This shows that the level of A3243G mutation is not always lower in rapidly dividing tissues such as blood than in muscle, as has been presumed until now.