The m.8529G>A variant (resulting in p.Trp55X in MT-ATP8 and p.M1M in MT-ATP6) has been reported in one individual with primary mitochondrial disease (PMID: 17953552). This is a male with hypertrophic cardiomyopathy, gross motor delay, exercise intolerance, dysarthria, ataxia, ophthalmoplegia, and elevated cerebrospinal fluid lactate. The variant was present at homoplasmy in muscle and fibroblasts. Although not included in this curation given additional details are not available, we are aware of one additional case by personal communication with ataxia and spastic paraplegia. There are no reported de novo occurrences of this variant to our knowledge. There are no reports of large families with this variant segregating with disease. This variant is absent in the GenBank dataset, Helix dataset, and gnomAD v3.1.2 (PM2_supporting). There are no in silico predictors for this type of variant in mitochondrial DNA. Cybrid studies showed that the homoplasmic mutant clones had statistically significant decreases in Complex V activity (PS3_supporting, PMID: 17954552). 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 August 12, 2024. Mitochondrial DNA-specific ACMG/AMP criteria applied (PMID: 32906214): PS3_supporting, PM2_supporting.