Equivalent reactions using pathological variant‐containing forms of TOP3A found that the p.Leu37Val (Fig 6C) and p.Met575Val (Fig 6I) variants found in the mitochondrial patient cohort, as well as the p.Ala176Val variant (Fig 6G) found in Bloom syndrome, showed a marked loss of decatenation activity. Here, TOP3A is linked to Bloom syndrome.