TTC21B and Jeune syndrome: In 2007, mutations in IFT80 were found to be associated with Jeune syndrome [54], a gene encoding a protein that is part of the multi-subunit IFT-B complex; however, almost all other mutations associated with human skeletal ciliopathies occur in genes encoding proteins that are part of the IFT-A complex involved in retrograde transport, i.e., IFT122 [23], WDR35/IFT121 [22, 28], TTC21B/IFT139 [55], WDR19/IFT144 [43], IFT140 [42], IFT43 [56], and DYNC2H1 [57], a subunit of the cytoplasmic dynein motor 2.