TTC21B and autosomal dominant polycystic kidney disease: Components of the Hh signaling pathway are elevated in human ADPKD tissue (Silva et al., 2018; Song et al., 2009), mice with mutations in the ciliary genes, Ift140, Thm1, and Arl13b (Jonassen et al., 2012; Li et al., 2016; Tran et al., 2014); two ADPKD models, the jck mutant and the conditional deletion of Pkd1 in postnatal mice (Tran et al., 2014); as well as in cystic murine metanephric kidney explants (Chan et al., 2010).