Cognitive deficits in Rett syndrome: what we know and what we need to know to treat them.

Rett syndrome is an autism spectrum disorder and a leading cause of severe mental retardation in girls. The nature of the cognitive abnormalities in Rett, as described in humans and other animal models, and its potential reversibility and treatment are the subject of this review. Rett syndrome is associated with severe mental retardation and a host of impairments that include social and motor deficits, and respiratory and bone abnormalities. More than 80% of Rett girls have mutations in the gene that encodes MeCP2, which is a protein with a complex set of functions that include transcriptional repression and activation. The complex phenotype associated with Rett and the knowledge of the causal genetic mutation provide a unique opportunity within the autism spectrum to explore the relationship between transcriptional control, brain abnormalities and specific behavioral functions, importantly the elusive cognitive dysfunctions associated with mental retardation. The nature of the cognitive abnormalities related to Rett and the potential reversibility and treatment of these abnormalities have not been studied as extensively as some of the other aspects of the Rett phenotype. The cognitive phenotype associated with Rett is also less well studied relative to that in other well known developmental disorders, such as Down syndrome and Fragile X. Nevertheless, some recent studies provide hope that the cognitive impairments, as well as other symptoms of Rett, can be rescued.