Heteroplasmy of mitochondrial genomes in clonal cultures from patients with Kearns-Sayre syndrome.

We have analyzed heteroplasmy of mitochondrial DNA in clonal cultures from two patients with Kearns-Sayre syndrome, and have found that individual muscle or fibroblast clones contained either a mixed (i.e. heteroplasmic) population of normal and deleted mitochondrial DNAs, or only normal mitochondrial DNAs (i.e. homoplasmic at a level of detection of less than 1% deleted genomes). The heteroplasmic clones grew significantly more slowly than did "homoplasmic" clones, probably due to defects of respiratory chain enzymes containing mtDNA-encoded polypeptides.