Pathogenic variants in autism gene KATNAL2 cause hydrocephalus and disrupt neuronal connectivity by impairing ciliary microtubule dynamics.

Enlargement of the cerebrospinal fluid (CSF)-filled brain ventricles (cerebral ventriculomegaly), the cardinal feature of congenital hydrocephalus (CH), is increasingly recognized among patients with autism spectrum disorders (ASD). KATNAL2, a member of Katanin family microtubule-severing ATPases, is a known ASD risk gene, but its roles in human brain development remain unclear. Here, we show that nonsense truncation of Katnal2 (Katnal2Δ17) in mice results in classic ciliopathy phenotypes, including impaired spermatogenesis and cerebral ventriculomegaly. In both humans and mice, KATNAL2 is highly expressed in ciliated radial glia of the fetal ventricular-subventricular zone as well as in their postnatal ependymal and neuronal progeny. The ventriculomegaly observed in Katnal2Δ17 mice is associated with disrupted primary cilia and ependymal planar cell polarity that results in impaired cilia-generated CSF flow. Further, prefrontal pyramidal neurons in ventriculomegalic Katnal2Δ17 mice exhibit decreased excitatory drive and reduced high-frequency firing. Consistent with these findings in mice, we identified rare, damaging heterozygous germline variants in KATNAL2 in five unrelated patients with neurosurgically treated CH and comorbid ASD or other neurodevelopmental disorders. Mice engineered with the orthologous ASD-associated KATNAL2 F244L missense variant recapitulated the ventriculomegaly found in human patients. Together, these data suggest KATNAL2 pathogenic variants alter intraventricular CSF homeostasis and parenchymal neuronal connectivity by disrupting microtubule dynamics in fetal radial glia and their postnatal ependymal and neuronal descendants. The results identify a molecular mechanism underlying the development of ventriculomegaly in a genetic subset of patients with ASD and may explain persistence of neurodevelopmental phenotypes in some patients with CH despite neurosurgical CSF shunting.

Disruption of mTORC1 rescues neuronal overgrowth and synapse function dysregulated by Pten loss.

Phosphatase and tensin homolog deleted on chromosome 10 (PTEN) is a negative regulator of AKT/mTOR signaling pathway. Mutations in PTEN are found in patients with autism, epilepsy, or macrocephaly. In mouse models, Pten loss results in neuronal hypertrophy, hyperexcitability, seizures, and ASD-like behaviors. The underlying molecular mechanisms of these phenotypes are not well delineated. We determined which of the Pten loss-driven aberrations in neuronal form and function are orchestrated by downstream mTOR complex 1 (mTORC1). Rapamycin-mediated inhibition of mTORC1 prevented increase in soma size, migration, spine density, and dendritic overgrowth in Pten knockout dentate gyrus granule neurons. Genetic knockout of Raptor to disrupt mTORC1 complex formation blocked Pten loss-mediated neuronal hypertrophy. Electrophysiological recordings revealed that genetic disruption of mTORC1 rescued Pten loss-mediated increase in excitatory synaptic transmission. We have identified an essential role for mTORC1 in orchestrating Pten loss-driven neuronal hypertrophy and synapse formation.