Cells in these mice lack primary cilia, and the conditional deletion of exons 11 and 12 of Ta3 in the limb leads to polydactyly and abnormal Shh signalling [25] while deletion in the central nervous system causes cerebellar hypoplasia and ataxia (key features of Joubert syndrome- a ciliopathy) with abnormal Shh signalling [31]. This evidence concerns the gene SHH and Joubert syndrome.