CDKL5 Deficiency Disorder Without Epilepsy

Cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) has epilepsy as a cardinal feature. Here we report two new female patients and review six previously published patients, one male and five females, with features of CDD but who never developed epilepsy. In contrast with the classical and severe CDD phenotype, they presented with milder gross motor delays, autism spectrum disorder, and no visual cortical impairment. Prolonged video electroencephalography was normal in adult cases but showed interictal frontal-temporal bilateral spikes and sharp waves in sleep in the three-year-old girl. Causative CDKL5 variants included two likely gene damaging (nonsense and frameshift) and six missense variants, being de novo or maternally inherited from asymptomatic females with skewed X-chromosome inactivation (two missense variants). Our data indicate that a milder form of CDD without epilepsy can occur in some cases without clear correlation with specific variants in the CDKL5 gene.