In addition, Pcm1−/− mice exhibited cerebellar hypoplasia and partially penetrant hydronephrosis, both of which can be caused by defective Hedgehog signaling, a signal transduction pathway dependent on cilia (Huangfu et al., 2003; Spassky et al., 2008; Wallace, 1999; Wechsler-Reya and Scott, 1999; Yu et al., 2002). The gene discussed is PCM1; the disease is hydronephrosis.