MECP2 and atypical Rett syndrome: In the case of specific examples of syndromic autism, the explanation for how a single gene mutation can result in such a complex neurodevelopmental disorder often lies in the complex function of the protein product of the mutated gene; in Rett syndrome, MeCP2 regulates the transcription of a host of genes yet to be identified, which may number over 1,000 (Horvath and Monteggia, 2017).