MECP2 and atypical Rett syndrome: The literature search was conducted on PubMed and Consensus (https://consensus.app/) using combinations of the keywords: “tryptophan metabolism,” “kynurenine,” “serotonin,” “indole,” AND each disorder name (e.g., “autism,” “ADHD,” “Rett syndrome,” “MeCP2 duplication”), with no time restriction and including both preclinical and clinical studies.