TTC21B and cranioectodermal dysplasia: Mutations in the genes encoding other members of this complex, IFT144 (WDR19), IFT121 (WDR35), IFT139 (TTC21B), can produce CED [23–26], SRPS [13, 34], a distinctive form of EVC [35], and ATD [17] overlapping phenotypes that imply disruption of similar biological mechanisms when the IFT-A complex is defective.