KATNIP (katanin-interacting protein, also known as KIAA0556) is a scaffold protein that regulates primary cilia formation and length through its interaction with ciliogenesis-associated kinase 1 (CILK1) 1. At the basal body, KATNIP binds CILK1 through its domain of unknown function (DUF), drastically elevating CILK1 protein levels and enabling the critical TDY phosphorylation required for CILK1 activation 1. This enhanced CILK1 activation increases phosphorylation of downstream substrates, suppressing cilia elongation and controlling ciliation frequency 2. KATNIP also interacts with the microtubule-severing katanin complex, suggesting a role in microtubule dynamics at the ciliary base 3. Pathogenic KATNIP variants cause Joubert syndrome 26, a ciliopathy characterized by cerebellar malformation and multi-systemic involvement 4. Disease variants exhibit loss-of-function phenotypes: truncated variants bind CILK1 but fail to support its activation and cilia length restriction 2. Notably, KATNIP-associated Joubert syndrome often lacks the classical molar tooth sign and presents with variable phenotypes including pituitary abnormalities, renal disease, esophageal atresia, and eye involvement 45. Recent evidence also links KATNIP defects to syndromic inherited retinal diseases 6, expanding its clinical relevance beyond classical ciliopathies.