Mediates phosphorylation of MECP2 (PubMed:15917271, PubMed:16935860). May regulate ciliogenesis (PubMed:29420175). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with MECP2. Expressed in brain, lung, kidney, prostate, ovary, placenta, pancreas and testis. Predominant transcript in brain. Autophosphorylated. Chromosomal aberrations involving CDKL5 are found in patients manifesting early-onset seizures and spams and psychomotor impairment. Translocation t(X;6)(p22.3;q14); translocation t(X;7)(p22.3;p15). The disease is caused by variants affecting the gene represented in this entry. Belongs to the protein kinase superfamily. CMGC Ser/Thr protein kinase family. CDC2/CDKX subfamily. It is uncertain whether Met-1 or Met-10 is the initiator.