CDKL5 and atypical Rett syndrome: Rett Syndrome (RTT) is a disorder caused by mutations in Methyl CpG binding protein 2 (MECP2), Forkhead box G1 (FOXG1) or Cyclin-dependent kinase-like 5 (CDKL5) genes [1–3] Although the phenotype of patients with mutations in MECP2 differs from the phenotype of patients with FOXG1 or CDKL5 mutations, there are some similarities in the clinical profile that overlap with RTT.