However, the absence of mitochondrial defects in skin fibroblasts from patients with mitochondrial defects in muscle is not uncommon.15 Nevertheless, given the dramatic impact of the TDP2 mutation on nuclear DNA repair, we suggest that any association of SCAR23 with mitochondrial disease is most likely an indirect or secondary dysfunction resulting from a nuclear disorder.16 Here, TDP2 is linked to inborn mitochondrial metabolism disorder.