WDR19 and cranioectodermal dysplasia: CED is genetically heterogeneous, with homozygous or compound heterozygous mutations found in either of IFT122 (mutated in classical CED phenotype), WDR35/IFT121 (associated with CED2), IFT43 (causing CED3), or WD Repeat Domain 19 (WDR19)/IFT144 (causing CED4) genes.