Mutations in the β-tubulin TUBB impair ciliogenesis and are associated with ciliopathy-like phenotypes

Tubulinopathies and neurodevelopmental ciliopathies are two groups of genetic disorders that cause structural brain malformations. Tubulinopathies result from mutations in tubulins, the building blocks of microtubules, most of which are dominant. Neurodevelopmental ciliopathies are mostly recessive disorders caused by defects in the primary cilium, an organelle that regulates key signaling pathways during brain development. Although more than 40 genes have been associated with neurodevelopmental ciliopathies, many patients still lack a known genetic cause. Here, we present a de novo heterozygous missense variant (p.G308S) in Tubulin Beta Class I (TUBB) identified in a patient showing features of both ciliopathy and tubulinopathy. While microtubules are essential for primary cilia formation and function, an association between tubulin mutations and neurodevelopmental ciliopathies has not been established. Using patient-derived cells and gene-edited isogenic cell lines, we show that the identified variant impairs the early stages of cilia formation by altering microtubule dynamics and structure. Consistent with this, mice carrying the variant display decreased ciliation in the cerebellum and kidney. Furthermore, we demonstrate that the disease mechanism is not haploinsufficiency and that other patient mutations in TUBB affect cilia formation, putting forward defective ciliogenesis as a contributing pathogenic factor in a subset of tubulinopathy patients.