The m.12239C>T variant in MT-TS2 was reviewed by the Mitochondrial Disease Nuclear and Mitochondrial Variant Curation Expert Panel as part of the variant pilot for mitochondrial DNA variant specifications (McCormick et al., 2020; PMID: 32906214). This variant is seen in 3.631% of individuals in the GenBank dataset (BA1), including in haplogroup B4a (90.9% of individuals). Furthermore, this variant is seen in the gnomAD dataset (v3.1.2) at an overall homoplasmic allele frequency of 0.2% including in haplogroup B at 7%. If an affected individual is not a member this haplogroup, further evaluation of the variant in that particular individual should be considered. The computational predictor MitoTIP suggests this variant does not impact the function of this tRNA with a score in the 5th percentile, as does HmtVar with a score of <0.35 (BP4). In summary, this variant meets criteria to be classified as benign. This classification was approved by the NICHD U24 Mitochondrial Disease Variant Curation Expert Panel as of August 20, 2020. Mitochondrial DNA-specific ACMG/AMP criteria applied: BA1, BP4.