The m.13514A>G (p.D393G) variant in MT-ND5 has been reported in at least 12 unrelated individuals with primary mitochondrial disease with onset ranging from childhood to adulthood and features variably consistent with Leigh syndrome and MELAS, as well as hypertrophic cardiomyopathy, optic atrophy, and neuropathy (PS4_moderate; PMIDs: 26341968, 25974876, 32504279, 20972245, 23847141, 21712854, 15576045, 14684687, 11198278). Heteroplasmy levels in affected individuals ranged from 55-70% in muscle, 12-55% in fibroblasts, 4-50% in blood, and 90% heart. This variant has been identified as a de novo occurrence in at least two probands with primary mitochondrial disease (PM6_supporting; PMIDs: 14684687, 11198278). There are no large families reported in the medical literature to consider for evidence of segregation. This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). Another variant at this amino acid position leading to a different amino acid change is classified as pathogenic by this Expert Panel – m.13513G>A (p. D393N, PM5). Cybrid studies showed a tight correlation between higher heteroplasmy level and lower complex I activity (PS3_supporting, PMID: 11198278). The computational predictor APOGEE gives a consensus rating of pathogenic with a score of 0.95 (Min=0, Max=1), which predicts a damaging effect on gene function (PP3). In summary, this variant meets criteria to be classified as likely pathogenic for primary mitochondrial disease inherited in a mitochondrial manner. This classification was approved by the NICHD/NINDS U24 Mitochondrial Disease Variant Curation Expert Panel on May 3, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PS4_moderate, PM6_supporting, PM2_supporting, PM5, PS3_supporting, PP3.