MECP2 and atypical Rett syndrome: Furthermore, as can be usefully exemplified by CDKL5, the complex interplay with other gene products, i.e., MECP2 (methyl CpG binding protein 2), which works as a transcriptional repressor/activator, results in partially overlapping, complex neurodevelopmental phenotypes falling within the so-called Rett syndrome spectrum [70].