Leigh syndrome appears to manifest at a high threshold level (≥90%), whereas other clinical phenotypes are associated with a lower mutant heteroplasmy, consistent with a previous observation.16 Several other MT‐ATP6 pathogenic variants, including m.9035T>C, m.9176T>C, and m.9185T>C, are associated with a very high phenotypic threshold level (>90%). Here, MT-ATP6 is linked to Leigh syndrome.