The m.7512T>C variant in MT-TS1 has been reported in four unrelated individuals with primary mitochondrial disease (PS4_moderate; PMIDs: 7669057, 17894844, 9778262). Clinical features in affected individuals include mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) as well as seizures, cognitive decline, dementia, muscle atrophy, muscle weakness, ataxia, developmental regression, and sensorineural hearing loss. Muscle biopsy in some cases showed ragged red fibers. Heteroplasmy levels in affected individuals ranged from 24% to homoplasmy. There are no reported de novo occurrences of this variant reported to our knowledge. The variant segregated with clinical features in all reported families (PP1_moderate; PMIDs: 7669057, 17894844, 9778262). This variant is absent in the GenBank dataset and gnomAD v3.1.2, and there is one heteroplasmic occurrence in the Helix dataset (PM2_supporting). The computational predictor MitoTIP suggests this variant is pathogenic (64.2 percentile) and HmtVAR predicts it to be pathogenic score of 0.75 (PP3). Single fiber analysis showed significantly higher levels of the variant in COX-negative fibers (n=10, median 97%, range: 94–99%) compared with COX-positive fibers (n=10, median 36%, range: 12–91%) (PS3_supporting, PMID: 17894844). 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 ClinGen Mitochondrial Disease Variant Curation Expert Panel on July 8, 2024. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PS4_moderate, PP1_moderate, PM2_supporting, PP3, PS3_supporting.