Mutations disrupting primary cilia cause retinal, renal, and cerebellar defects, and misregulated Sonic hedgehog signaling. A new mouse mutant in the TTBK2 kinase fails to make cilia, and shows neural tube and Sonic hedgehog signaling defects. Ciliary targeting mutations in human TTBK2 are linked to spinocerebellar ataxia, suggesting cilia protect from neurodegeneration.
