Ji Eun Lee^1,2, Jennifer L Silhavy^1,2, Maha S Zaki³, Jana Schroth^1,2, Stephanie L Bielas^1,2, Sarah E Marsh^1,2, Jesus Olvera^1,2, Francesco Brancati^4,5, Miriam Iannicelli⁴, Koji Ikegami⁶, Andrew M Schlossman^1,2, Barry Merriman⁷, Tania Attie-Bitach⁸, Clare V Logan⁹, Ian A Glass^10,11, Andrew Cluckey¹², Carrie M Louie^1,2, Jeong Ho Lee^1,2, Hilary R Raynes^13-15, Isabelle Rapin^13-15, Ignacio P Castroviejo¹⁶, Mitsutoshi Setou⁶, Clara Barbot¹⁷, Eugen Boltshauser¹⁸, Stanley F Nelson⁷, Friedhelm Hildebrandt¹², Colin A Johnson⁹, Daniel A Doherty^10,11, Enza Maria Valente^4,19 & Joseph G Gleeson^1,2,*

¹Department of Neurosciences, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California, USA. ²Neurogenetics Laboratory, Institute for Genomic Medicine, Department of Pediatrics, University of California, San Diego, La Jolla, California, USA. ³Clinical Genetics Department, Human Genetics and Genome Research Division, National Research Centre, Dokki, Egypt. ⁴Casa Sollievo della Sofferenza (CSS) Hospital, CSS-Mendel Laboratory, San Giovanni Rotondo, Italy. ⁵Department of Biopathology and Diagnostic Imaging, Medical Genetics Unit, Tor Vergata University, Rome, Italy. ⁶Department of Cell Biology and Anatomy, Hamamatsu University School of Medicine, Hamamatsu, Japan. ⁷Department of Human Genetics, Pathology and Laboratory Medicine, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California, USA. ⁸Departement de Genetique, Institut National de la Sante et de la Recherche Medicale (INSERM) U781, Hopital Necker.Enfants Malades, Universite Paris Descartes, Paris, France. ⁹Section of Ophthalmology and Neurosciences, Leeds Institute of Molecular Medicine, St James’s University Hospital, Leeds, UK. ¹⁰Department of Pediatrics, Division of Developmental Medicine, University of Washington, Seattle Children’s Hospital, Seattle, Washington, USA. ¹¹Division of Genetic Medicine, University of Washington, Seattle Children’s Hospital, Seattle, Washington, USA. ¹²Department of Pediatrics and Communicable Diseases, Howard Hughes Medical Institute, University of Michigan, Ann Arbor, Michigan, USA. ¹³Saul R. Korey Department of Neurology, Albert Einstein College of Medicine, New York, New York, USA. ¹⁴Department of Pediatrics, Albert Einstein College of Medicine, New York, New York, USA. ¹⁵Rose F. Kennedy Intellectual and Developmental Disabilities Research Center, Albert Einstein College of Medicine, New York, New York, USA. ¹⁶Pediatric Neurology Service, University Hospital La Paz, Madrid, Spain. ¹⁷Servico de Neuropediatria, Hospital de Criancas Maria Pia, Porto, Portugal. ¹⁸Department of Pediatric Neurology, University Children’s Hospital of Zurich, Zurich, Switzerland. ¹⁹Department of Medical and Surgical Pediatric Sciences, University of Messina, Messina, Italy. ^*Correspondence should be addressed to J.G.G.

Tubulin glutamylation is a post-translational modification that occurs predominantly in the ciliary axoneme and has been suggested to be important for ciliary function^1,2. However, its relationship to disorders of the primary cilium, termed ciliopathies, has not been explored. Here we mapped a new locus for Joubert syndrome (JBTS)³, which we have designated as JBTS15, and identified causative mutations in CEP41, which encodes a 41-kDa centrosomal protein⁴. We show that CEP41 1 is localized to the basal body and primary cilia, and regulates ciliary entry of TTLL6, an evolutionarily conserved polyglutamylase enzyme⁵. Depletion of CEP41 causes ciliopathy-related phenotypes in zebrafish and mice and results in glutamylation defects in the ciliary axoneme. Our data identify CEP41 mutations as a cause of JBTS and implicate tubulin post-translational modification in the pathogenesis of human ciliary dysfunction.