Molecular Functions of MECP2 in Rett Syndrome Pathology
As reviewed by Sharifi and Yasui, MECP2 protein, encoded by the MECP2 gene binds to DNA with a high affinity for CpG methylated DNA sites and affects transcription. MECP2 can bind to 5mc (5-methylcytosine) and 5hmc (5-hydroxymethylcytosine) with similar affinity, and these dinucleotides account for the majority of MECP2 binding sites in the mammalian genome. MECP2 is involved in higher order chromatin organization and appears necessary for compacting chromosomes. MECP2 binding to DNA influences mRNA splicing events. MECP2 also appears to function in DNA repair processes. MECP2-/+ deficient female mice have elevated rates of cell death when exposed to DNA damaging agents and are prone to early senescence. Interactive pathway map
An interactive pathway map of Rett syndrome has been published. Diagnosis
Prior to the discovery of a genetic cause, Rett syndrome had been designated as a pervasive developmental disorder by the Diagnostic and Statistical Manual of Mental Disorders (DSM), together with the autism spectrum disorders. Some argued against this conclusive assignment because RTT resembles non-autistic disorders such as fragile X syndrome, tuberous sclerosis, or Down syndrome that also exhibit autistic features. After research proved the molecular mechanism, in 2013 the DSM-5 removed the syndrome altogether from classification as a mental disorder.Rett syndrome diagnosis involves close observation of the childs growth and development to observe any abnormalities in regards to developmental milestones. A diagnosis is considered when decreased head growth is observed.
In this form of Rett syndrome, the patients have epilepsy before 5 months of age.The definition itself of the Rett syndrome has been refined over the years: as the atypical forms subsist near to the classical form (Hagberg & Gillgerg, 1993), the "Rett Complex" terminology has been introduced. Cause
Genetically, Rett syndrome (RTT) is caused by mutations in the gene MECP2 located on the X chromosome (which is involved in transcriptional silencing and epigenetic regulation of methylated DNA), and can arise sporadically or from germline mutations. In less than 10% of RTT cases, mutations in the genes CDKL5 or FOXG1 have also been found to resemble it. Rett syndrome is initially diagnosed by clinical observation, but the diagnosis is definitive when there is a genetic defect in the MECP2 gene. It has been argued that Rett syndrome is in fact a neurodevelopmental condition as opposed to a neurodegenerative condition. One piece of evidence for this is that mice with induced Rett Syndrome show no neuronal death, and some studies have suggested that their phenotypes can be partially rescued by adding functional MECP2 gene back when they are adults. This information has also helped lead to further studies aiming to treat the disorder. Sporadic mutations
In at least 95% of Rett syndrome cases, the cause is a de novo mutation in the child. That is, it is not inherited from either parent.