CHEK1 and Leigh syndrome: Of note, alteration in at least one of the DNA damage response and repair genes (ERCC2, ERCC3, ERCC4, ERCC5, BRCA1, BRCA2, RAD50, RAD51, RAD51B, RAD51C, RAD51D, RAD52, RAD54L, NBN, MRE11A, ATM, ATR, MDC1, CHEK1, CHEK2, PALB2, BRIP1, FANCA, FANCC, BLM, MUTYH, RECQL4, PARP1, and POLE) was found in 94% of the patients with LS, compared with 23% in the sporadic cohort (P < .001).