Mutant POLG2 disrupts DNA polymerase gama subunits and causes progressive external opthalmoplegia

A heterozygous dominant mutation in POLG2 is described, the gene encoding the p55 accessory subunit of pol gama, that causes progressive external opthalmoplegia with multiple mtDNA deletions and cytochrome c oxidase-(COX) deficient muscle fibres. The progressive accumulation of mtDNA deletions causes COX deficiency in muscle fibres and results in the clinical phenotype.