MECP2 (Methyl-CpG-Binding Protein 2 Epigenetic Regulator)
MECP2 (methyl-CpG binding protein 2; HGNC:6990, NCBI Gene ID 4204) is a human locus mapped to chromosome band Xq28 that encodes chromatin reader Methyl-CpG-binding protein 2 (486 aa e2 / 498 aa e1 isoforms). MECP2 acts in 5-methylcytosine & 5-hydroxymethylcytosine chromatin reading and NCoR/HDAC3 recruitment, together with BDNF (Brain-Derived Neurotrophic Factor), HDAC3 (Histone Deacetylase 3), and IGF1 (Insulin-Like Growth Factor 1). Encodes the X-linked methyl-CpG-binding chromatin reader mutated in Rett syndrome.
Approved Symbol
MECP2
Chromosomal Locus
Xq28
Encoded Product
Chromatin reader Methyl-CpG-binding protein 2 (486 aa e2 / 498 aa e1 isoforms)
Primary Pathway
5-methylcytosine & 5-hydroxymethylcytosine chromatin reading and NCoR/HDAC3 recruitment
Clinical / Therapeutic Role
Loss-of-function causes Rett syndrome; Xq28 duplication causes MECP2 duplication syndrome
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 4-exon X-linked gene at Xq28 generating two alternatively spliced isoforms (MeCP2-e1 and MeCP2-e2) that share a conserved N-terminal methyl-CpG-binding domain (MBD) and a transcriptional repression domain (TRD) containing an NCoR/SMRT co-repressor interaction motif (NID).
Cellular & Tissue Expression Profile: Expressed ubiquitously across tissues but reaches near-histone stoichiometry in mature post-mitotic central nervous system neurons, where there are approximately 16 million MeCP2 molecules per neuronal nucleus.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Binds methylated CG (mCG) and methylated CA (mCAC) dinucleotides across neuronal chromatin and recruits the NCoR1/SMRT-HDAC3 deacetylase complex to dampen transcription of long synaptic genes while also facilitating activity-dependent expression of neurotrophic loci such as BDNF.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Heterozygous de novo loss-of-function mutations in females cause classic Rett syndrome, marked by normal infancy followed at 6–18 months by developmental regression, loss of purposeful hand skills, stereotypic hand wringing, gait ataxia, and respiratory dysrhythmias, whereas hemizygous Xq28 duplications in males cause MECP2 duplication syndrome, illustrating extreme dosage sensitivity.
Therapeutic & Clinical Pharmacology: Because neuronal MeCP2 expression must remain within a narrow physiological window, next-generation AAV9 gene replacement vectors incorporate synthetic miRNA-responsive self-regulating 3-prime UTRs (such as TSHA-102 and NGN-401), alongside X-chromosome reactivation strategies, RNA base editing, and FDA-approved trofinetide (IGF-1 N-terminal tripeptide analog).