The m.15197T>C (p.S151P) variant in MT-CYTB has been reported in one individual with primary mitochondrial disease to date. This individual had exercise intolerance in early childhood and had the variant present at 80% heteroplasmy in muscle. The variant was undetectable in blood and skin fibroblasts. Complex III activity was reduced at 17% of controls in muscle, 28% in blood, and 50% in skin fibroblasts (PMID: 11454242). There are no reports of large families with this variant segregating with disease. There are no reported de novo occurrences of this variant to our knowledge. This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). The computational predictor APOGEE gives a consensus rating of pathogenic with a score of 0.72 (Min=0, Max=1), which predicts a damaging effect on gene function (PP3). There are no cybrids, single fiber studies, or other functional assays reported on this variant. 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 January 8, 2024. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PM2_supporting, PP3.