The m.8296A>G variant in MT-TK has been reported in 18 unrelated individuals with primary mitochondrial disease with varying phenotypes (diabetes, hypertrophic cardiomyopathy, optic atrophy, sensorineural hearing loss, and generalized epilepsy; 10 subjects reported in PMIDs: 9802769, 9571188, 10525672; additional subjects reported in PMIDs: 10737988, 12504210, 18651333, 20143911, 37573175), however analyses for other genetic etiologies were limited in these affected individuals precluding their inclusion in this curation. The variant was present in some affected individuals at homoplasmy and in others at heteroplasmy. In at least one family, the variant was present at homoplasmy in the proband and in his healthy mother and sister (PMID: 18651333). There are no reported de novo occurrences to our knowledge. This variant is present in population databases and is seen in individuals from several different haplogroups (MITOMAP: 0.061%, 38/61,883; gnomAD v3.1.2: 0.044%, 25/56,432 homoplasmic occurrences, one heteroplasmic occurrence; Helix: 0.048%, 94/195,893 homoplasmic occurrences). The computational predictor MitoTIP suggests this variant is pathogenic (72.3 percentile) and HmtVAR predicts it to be pathogenic score of 0.85 (PP3). Single fiber testing showed similar levels of the variant in COX-negative ragged red fibers and normal fibers (PMID: 9932960), and cybrid studies showed no significant differences from wild type (PMID: 11857739). 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 February 4, 2025. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PP3.