TTC21B and nephronophthisis: In C. elegans, loss of IFT 139 leads to formation of abnormal, short cilia (Niwa, 2016), and mutations in the human gene encoding IFT139 (TTC21B) have been linked to nephronophthisis and thoracic dystrophy (Davis et al., 2011; Huynh Cong et al., 2014).