A new knockin mouse carrying the E364X patient mutation for CDKL5 deficiency disorder: neurological, behavioral and molecular profiling.

CDKL5 deficiency disorder (CDD) is a rare neurodevelopmental syndrome caused by mutations in the X-linked CDKL5 gene. Hundreds of pathogenic variants have been described, associated with a significant phenotypic heterogeneity observed among patients. To date, different knockout mouse models have been generated. Here we present a new knockin CDKL5 mouse model carrying a humanized, well-characterized nonsense variant (c.1090G > T; p.E364X) described in the C-terminal domain of the CDKL5 protein in a female patient with a milder phenotype. Both male and female Cdkl5 ^E364X mice were analyzed. The novel Cdkl5 ^E364X mouse showed altered neurological and motor neuron maturation, hyperactivity, defective coordination and impaired memory and cognition. Gene expression analysis highlighted an unexpected reduction of Cdkl5 expression in Cdkl5 ^E364X mice brain tissues, with a significant increase in overall neuron-specific gene expression and an area-dependent alteration of astrocyte- and oligodendrocyte-specific transcripts. Moreover, our results showed that the loss of CDKL5 protein had the most significant impact on the cerebellum and hippocampus, compared to other analyzed tissues. A targeted analysis to study synaptic plasticity in cerebellum and hippocampus showed reduced Gabra1 and Gabra5 expression levels in females, whereas Gabra1 expression was increased in males, suggesting an opposite, sex-dependent regulation of the GABA receptor expression already described in humans. In conclusion, the novel Cdkl5^E364X mouse model is characterized by robust neurological and neurobehavioral alterations, associated with a molecular profile related to synaptic function indicative of a cerebellar GABAergic hypofunction, pointing to Gabra1 and Gabra5 as novel druggable target candidates for CDD.