CDKL5 is a gene that provides instructions for making a protein called cyclin-dependent kinase-like 5 also known as serine/threonine kinase 9 (STK9) that is essential for normal brain development. Mutations in the gene can cause deficiencies in the protein. The gene regulates neuronal morphology through cytoplasmic signaling and controlling gene expression. The CDKL5 protein acts as a kinase, which is an enzyme that changes the activity of other proteins by adding a cluster of oxygen and phosphorus atoms (a phosphate group) at specific positions. Researchers are currently working to determine which proteins are targeted by the CDKL5 protein. The CDKL5 protein acts as a kinase, which is an enzyme that modulates the activity of other proteins by adding a phosphate group to specific positions. The CDKL5 protein regulates neuronal morphology through cytoplasmic signaling and by controlling gene expression, playing a crucial role in the development and maintenance of the nervous system. Studies have shown that the CDKL5 protein interacts with various signaling pathways and plays a role in controlling neurotransmitter release, synaptic plasticity, and cell survival. The CDKL5 protein has also been shown to regulate the activity of genes involved in neuronal development and the formation of synaptic connections. Researchers are actively working to better understand the role of the CDKL5 protein in brain development and the underlying mechanisms of CDKL5 disorders. Further studies are needed to determine which proteins are targeted by the CDKL5 protein, as well as to develop effective treatments for individuals affected by CDKL5 disorders. Mutations Mutations in the CDKL5 gene cause CDKL5 deficiency disorder. CDKL5 Deficiency had been thought of as a variant of Rett's Syndrome due to some similarities in the clinical presentation, but it is now known to be an independent clinical entity caused by mutations in a distinct X-linked gene, and is considered separate from Rett Syndrome rather than a variant of it. While CDKL5 is primarily associated with girls, it has been seen in boys as well. This disorder includes many of the features of classic Rett syndrome (including developmental problems, loss of language skills, and repeated hand wringing or hand washing movements), but also causes recurrent seizures beginning in infancy. Some CDKL5 mutations change a single protein building block (amino acid) in a region of the CDKL5 protein that is critical for its kinase function. Other mutations lead to the production of an abnormally short, nonfunctional version of the protein.