The m.7471dup variant in MT-TS1 has been reported in >16 unrelated individuals with primary mitochondrial disease across several haplogroups. This variant is most commonly associated with sensorineural hearing loss however affected individuals can also have other features. Affected individuals have been reported with features including MELAS, cerebellar ataxia, myoclonus, epilepsy, white matter disease, intellectual disability, cerebellar atrophy, exercise intolerance, and hypotonia; and this variant has been seen in affected individuals in the homoplasmic and heteroplasmic states (PS4; PMIDs: 7581383, 9708714, 9832034, 9778262, 9778273, 10094190, 15482956, 11378827, 15292920, 15482956, 11378827, 15292920, 1533431, 16368237, 17637808, 15833431, 16368237). This variant segregated with disease in multiple affected members in multiple families and several healthy family members had lower to undetectable levels of the variant (PP1_moderate, PMIDs: 7581383, 9708714). Cybrid studies supported the functional impact of this variant (PS3_supporting; PMID: 10545608). There are no de novo occurrences to our knowledge. There are no in silico predictors for this type of variant in mitochondrial DNA. In summary, this variant meets criteria to be classified as likely pathogenic however this Expert Panel elected to modify the classification to pathogenic given the overwhelming evidence of pathogenicity. Furthermore, the mitochondrial DNA variant specifications are known to not be optimized for pathogenic variants that tend to be homoplasmic in nature, have reduced penetrance, and/or variants that are insertions. This classification was approved by the NICHD/NINDS U24 ClinGen Mitochondrial Disease Variant Curation Expert Panel on November 14, 2022. Mitochondrial DNA-specific ACMG/AMP criteria applied(PMID: 32906214): PS4, PP1_moderate, PS3_supporting.