SMAD4 and familial colorectal cancer type X: Although the genetic causes of FCCTX are still unknown, several studies identified some CRC predisposing genes including BRCA2, SEMA4A, APC, BMPR1A, NTS, CDH18, RPS20, GREM1, BCR, KIF24, GALNT12, ZNF367, HABP4, GABBR2, TP53, SMAD4, and BMP4 (11–13, 22–24).