MECP2 and atypical Rett syndrome: Furthermore, in animal models of Rett syndrome (RTT), a devastating neurodevelopmental disorder, which is caused by a mutation in the X-linked MECP2 gene encoding methyl-CpG-binding protein 2, microglia release an abnormally high level of glutamate, causing excitotoxicity that may contribute to dendritic and synaptic abnormalities in RTT [99].