In a groundbreaking 2001 paper, the heterozygous POLG c.2864A>G/p.Y955C mutation (hereafter POLG Y955C) cosegregated with autosomal dominant progressive external ophthalmoplegia (adPEO) in a family, establishing that a POLG mutation causes the disorder (9). The gene discussed is POLG; the disease is autosomal dominant progressive external ophthalmoplegia.