CDKL5 and atypical Rett syndrome: Further, a rarer variant of Rett Syndrome characterised by mutations in the CDKL5 (Cyclin-Dependent Kinase-Like 5) gene, a regulator of MeCP2 which also has important roles in brain development and neuronal maturation [8], suggests a common underlying mechanism related to abnormalities in synapse formation in Rett Syndrome.