Single-cell analysis of mitochondrial DNA in patients and a carrier of the tRNA(Leu)(UUR) gene mutation.

We examined heteroplasmy of mutated mitochondrial DNA in single peripheral lymphocytes derived from 4 individuals carrying the nt 3243 A-to-G mutation, including two patients with MELAS, a patient with cardiomyopathy, deafness and diabetes mellitus, and the asymptomatic mother of one of the MELAS patients. In these subjects, all lymphocytes examined were heteroplasmic to different degrees, with a wider range of heteroplasmy evident in the symptomatic patients than in the healthy carrier.