The genetic aetiology of FCCTX is most likely heterogenous and may include rare pathogenic germline variants in e.g. heterozygous MUTYH, CHEK2, BRCA2, POLE, POLD1, SEMA4A, BMPR1A, RPS20 or OGG1 or modifying single nucleotide polymorphisms in SEMA4A, EXO1, TGFBR1, or NUDT1 [1, 5, 9, 10, 12, 24, 25, 29, 40]. This evidence concerns the gene SEMA4A and familial colorectal cancer type X.