This is further supported by observations that COSMIC tumor mutational signatures (SBS18/SBS36), indicative of defective base excision repair, are present only in biallelic MUTYH pathogenic variants carriers but not in CRC tumors of monoallelic MUTYH pathogenic variant carriers.8 Similarly, monoallelic carriers of either of the 2 common pathogenic variants in NTHL1, c.268C>T:p.Gln90Ter or c.859C>T:p.Gln287Ter, were not associated with an increased risk of CRC. The gene discussed is NTHL1; the disease is colorectal carcinoma.