The m.8969G>A (p.S148N) variant in MT-ATP6 has been reported in at least five individuals from four families in the literature with features including nephrotic syndrome, developmental delay, seizures, stroke-like episodes, muscle weakness, brain atrophy, agenesis of the corpus callosum, hearing loss, Wolff-Parkinson-White syndrome, increased fasting level of glucose, liver steatosis, and failure to thrive, with heteroplasmy levels ranging from 61-96% (PS4_moderate; PMIDs: 25037980, 29350304, 27812026, 27450679). Additionally, this expert panel knew of two local families with affected individuals with this variant that the expert panel agreed to include. The variant was de novo in two of the four families reported in the literature (PS2_moderate; PMIDs: 25037980, 27450679). This variant segregated with disease in multiple affected members in one family and several healthy family members had lower to undetectable levels of the variant (PP1_moderate; PMIDs: 29350304). This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). Studies in cybrids and yeast support the functional impact of this variant (PS3_supporting; PMID: 27812026). The computational predictor APOGEE gives a consensus rating of pathogenic with a score of 0.57 (Min=0, Max=1), which predicts a damaging effect on gene function (PP3). 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 Mitochondrial Disease Variant Curation Expert Panel on March 28, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PS4_moderate, PS2_moderate, PP1_moderate, PM2_supporting, PS3_supporting, PP3.