Deficiency of cyclin-dependent kinase-like 5 causes spontaneous seizures in neonatal mice

Cyclin-dependent kinase-like 5 (CDKL5), an X-linked gene encoding a serine-threonine kinase, is enriched in the mammalian forebrain and critical for neuronal maturation and synaptic function. Mutations in this gene cause CDKL5 deficiency disorder (CDD) that is characterized by early-onset epileptic seizures, autistic behaviors and intellectual disability. Although numerous CDD symptoms have been recapitulated in mouse models, spontaneous seizures have not been reported in mice with CDKL5 deficiency. Here, we present the first systematic study of spontaneous seizures in a mouse model of CDD. Through wireless electroencephalographic (EEG) recording and simultaneous videotaping, we observed epileptiform discharges accompanied with ictal behaviors in pups lacking CDKL5 at a selective time window during the pre-weaning period. The seizure-like patterns of EEG showed robust increase in total number of spike events, the total number and duration of bursts in Cdkl5 null pups compared to wild-type littermate controls at the age of postnatal day 12 (P12). The mutants displayed not only jerky and spasm-like movements during the prolonged bursts of discharges at P12, but also strengthened ictal grasping in both juvenile stage and adulthood. In addition, loss of CDKL5 remarkably reduced the phosphorylation of K+/Cl- co-transporter 2, which may impede GABA-mediated inhibition, in the cortex of P12 mouse pups. Our study reveals previously unidentified phenotypes of early-onset seizures in CDKL5-deficient mice, highlights the translational value of mouse models of CDD and provides a potential molecular target for early diagnosis and treatment for CDD. Significance StatementCyclin-dependent kinase-like 5 (CDKL5) is an X-linked gene encoding a serine-threonine kinase. Mutations in this gene cause CDKL5 deficiency disorder (CDD), a rare disease characterized by developmental delays, autistic behaviors and early-onset epilepsy. Even though many symptoms of CDD patients have been phenocopied in mice, spontaneous seizures are yet to be reported in mouse models of CDD. Here, for the first time, we identified early-onset seizures and ictal behaviors in neonatal pups of CDKL5-deficient mice. Loss of CDKL5 also selectively reduced protein levels of phosphorylated K+/Cl-cotransporter 2 in neonatal cortex of mice. Our study reveals an indispensible role of CDKL5 in regulating neuronal excitability in developing brains and highlights the translational significance of the CDD mouse models.