CCDC8 and 3M syndrome: The prevalence of 3M syndrome has not yet been clearly defined, but pathogenic variants of three genes, namely, CUL7 (3M1, MIM #273750), OBSL1 (3M2, MIM #612921), and CCDC8 (3M3, MIM #614205), were responsible for 77.5%, 16%, and <5% of 3M syndrome cases, respectively (Hanson et al., 2009, 2011; Huber et al., 2009, 2011).