Rett syndrome (RTT), an X-linked neurodevelopment disorder affecting almost exclusively females, is associated with a single monogenic mutation (methyl-CpG binding protein 2, MeCP2) in up to 95% of cases [1], more rarely by mutations in cyclin-dependent kinase-like 5 (CDKL5) [2], and forkhead box protein G1 (FOXG1) gene [3]. The gene discussed is CDKL5; the disease is atypical Rett syndrome.