Notably, although early linkage or targeted sequencing studies in large multiplex CH families have found four risk genes, including L1CAM (OMIM# 307000) (Rosenthal, Jouet, Jouet, & Kenwrick, 1992), CCDC88C (OMIM# 236600) (Ekici et al., 2010), MPDZ (OMIM# 615219) (Al‐Dosari et al., 2013), and AP1S2 (OMIM# 300629) (Tarpey et al., 2006), these findings in aggregate explain less than 5% of CH cases, suggesting additional risk genes await discovery. This evidence concerns the gene L1CAM and cyclic hematopoiesis.