CDKL5 deficiency disorder (CDD) is an X-linked disorder resulting from mutations in the CDKL5 gene, which encodes a kinase involved in synaptic plasticity, glutaminergic signaling, and dendrite formation. 1,2 Girls are ~4-fold more often affected, but boys are more severely affected. The incidence is ~1 per 50 000 births. 1 CDD typically presents in the first 3 months of life with treatment-resistant epilepsy (TRE) and hypotonia followed by global developmental delays and cortical visual impairment. 1,2 Infantile spasms and other generalized or mixed generalized/focal epilepsies may be the initial seizure type, with evolution to multiple seizure types that often straddle or fail to conform to standard classifications. Seizures often respond initially but recur, and most children have daily seizures despite multiple antiseizure medication (ASM) regimens. 1,2 Fenfluramine (FFA) enhances serotonin release, positively modulates sigma-1 receptors, 3 and has potent, durable efficacy in treating convulsive seizures in Dravet syndrome and