The m.10197G>A (p.A47T) variant in MT-ND3 has been reported in at least 22 probands with primary mitochondrial disease. Affected individuals had variable ages of onset (first months of life to childhood to adulthood). Features included Leigh syndrome, Leigh syndrome/MELAS overlap, and LHON with good visual recovery. Heteroplasmy levels were variable among tissues and affected individuals, and ranged from 10% (in an individual with LHON) to homoplasmy (in an individual with Leigh syndrome; PS4; PMIDs: 15372108, 17152068, 17413873, 18977334, 19458970, 20818383, 20972245, 24708134, 30128709, 30199507, 30776730, 32045392; two articles with no PMIDs: Pereira et al., 2019; JIEMS, 2019, Vol7: e20180003; Huang et al., 2017, J Clin Exp Ophthalmol 2017, 8:4). 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: 17152068, 17413873, 30128709, 30776730). This variant occurred de novo in at least three individuals (PM6_moderate, PMIDs: 24708134, 17413873; article with no PMID: Huang et al., 2017, J Clin Exp Ophthalmol 2017, 8:4). There are four occurrences of this variant in the GenBank dataset, and three of these four are not listed as patient sequences. However, upon discussion on the Expert Panel (EP) call, concern was raised that phylogenetic studies use patient samples and submit these to GenBank. This variant is absent in gnomAD v3.1.2 and in Helix dataset so the EP agreed to consider this supporting line of evidence (PM2_supporting). Cybrid studies showed a correlation between higher heteroplasmy level and lower complex I activity (PS3_supporting, PMID: 17152068). The computational predictor APOGEE gives a consensus rating of pathogenic with a score of 0.88 (Min=0, Max=1), which predicts a damaging effect on gene function (PP3). 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/NINDS U24 Mitochondrial Disease Variant Curation Expert Panel on July 25, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PM2_supporting, PP3, PP1_moderate, PS3_supporting, PM6_moderate, PS4.