The m.583G>A variant in MT-TF has been reported in two unrelated individuals with primary mitochondrial disease. The first was a woman with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) who also had retinal dystrophy, ataxia, and dystonic posturing (PMID: 9771776). The second reported individual had myopathy and retinal dystrophy (PMID 16806928). The variant in the first case was heteroplasmic in the patient’s muscle (58%) but undetectable blood. The variant was also undetectable in the mother's blood. In the second case, the variant was heteroplasmic (79%) in the patient’s muscle but undetectable in other tissues. The ages of onset in the two cases were 12 and 17 years, respectively (PS4_supporting). There are no large families reported in the medical literature to consider for evidence of segregation. The variant was reported de novo in one case report as it was absent in mother’s blood (PMID: 9771776), however the variant was also absent in the proband’s blood, no additional tissues were tested, and technology performed at the time of publication would not detect low heteroplasmy levels of the variant. There are no other reports of de novo occurrences to our knowledge. The computational predictor MitoTIP suggests this variant is pathogenic, scoring in the 93.1 percentile, and HmtVAR also predicts it to be pathogenic with a score of 0.85 (PP3). The m.583G>A variant is absent in the GenBank dataset, the Helix dataset, and gnomAD3.1.2 (PM2_supporting). A single-fiber study (PMID: 16806928) showed the variant heteroplasmy to be higher in COX-negative fibers (78±22%; n = 11) than in COX-positive fibers (45±16%; n = 15; P < 0.001). An aminoacylation study (PMID: 17878308) showed significant losses in aminoacylation efficiency for this variant (PS3_supporting). In summary, this variant meets criteria to be classified as uncertain significance for primary mitochondrial disease inherited in a mitochondrial manner. This classification was approved by the NICHD/NINDS U24 ClinGen Mitochondrial Disease Variant Curation Expert Panel on October 10, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PS4_supporting, PS3_supporting, PP3, PM2_supporting.