The m.8993T>G (p.L156R) variant in MT-ATP6 has been reported in >16 individuals with primary mitochondrial disease (PS4; PMIDs: 2137962, 8250532, 8240109, 7605802, 8505474, 9221962, 10208283, 16525806, 10660580). There are several reports of de novo occurrences of this variant (PM6_strong, PMIDs: 29602698, 27450679, 12134275). This variant is located at the same amino acid position as another well-known pathogenic variant, m.8993T>C (p.L156P) (PM5). This variant segregated with disease in multiple affected members in multiple families and several healthy family members had lower to undetectable levels of the variant (PP1_moderate; PMIDs: 2137962, 1436530, 1550128, 8095070, 9221962). This variant is absent in population databases after removing known patients with mitochondrial disease (PM2_supporting). In silico tools (APOGEE) predict this variant to be pathogenic (PP3). Cybrid studies supported the functional impact of this variant (PS3_supporting; PMID: 14998933, 8078883, 19875463). In summary, this variant meets criteria to be classified as pathogenic for primary mitochondrial disease inherited in a mitochondrial manner. This classification was approved by the NICHD U24 Mitochondrial Disease Variant Curation Expert Panel on March 22, 2021. Mitochondrial DNA-specific ACMG/AMP criteria applied: PS3_supporting, PS4, PM2_supporting, PM5, PM6_strong, PP1_moderate, PP3).