Rett syndrome is a progressive neurodevelopmental disorder and one of the most common causes of mental retardation in females, with an incidence of about 1 in 10,000. Babies with Rett syndrome seem to develop normally until 6-18 months, at which point they begin showing a reduction in brain size and become prone to seizures and autism.
The syndrome is caused by mutation of MECP2, a gene on the X chromosome. So, females with one intact copy of the gene usually survive into adulthood, despite their neurological problems, whereas male embryos that carry the mutation--on their single X chromosome--die during embryogenesis. The protein encoded by the 'Rett' gene, methyl-CpG-binding protein 2 (MeCP2), binds to DNA segments that have been modified by methylation and represses the production of messenger RNA from adjacent genes. As this kind of transcriptional repression is thought to control a large number of genes, especially during embryonic development, it has been hypothesized that Rett syndrome might result from widespread aberrations during early stages of development that affect the brain and possibly other organs.
Two studies now indicate that MeCP2 is required for the maintenance of neuronal function, mostly after birth (Nature Genetics, Vol. 27, No. 3, 02 Mar 2001). Groups led by Rudolf Jaenisch (of the Massachusetts Institute of Technology, Massachusetts) and Adrian Bird (of the University of Edinburgh, UK) have engineered mice that lack functional MeCP2. They find that the mutant mice have symptoms reminiscent of Rett syndrome, including small brains and small neurons. They observed the same syndrome in mice lacking expression of MeCP2 in the brain, showing that Rett syndrome is not due to developmental defects in organs other than the brain. Finally, ablation of MeCP2 in mouse brain after birth resulted in a Rett-like syndrome--although at a later age than in mice lacking MeCP2 from conception. These studies indicate that Rett syndrome is primarily due to the lack of MeCP2 in neurons and that it is a disruption in the maintenance of neuronal function after birth that is critical to the disorder. As it is easier to treat newborns than to correct defects in embryonic development, these findings hold promise for the therapy of Rett syndrome.
Dr. Rudolf Jaenisch
Massachusetts Institute of Technology
Cambridge, Massachusetts, USA
Telephone: +1 (617) 258-5186
Fax: +1 (617) 258-6505
Dr. Adrian Bird
University of Edinburgh
Telephone: (44) 131-650-5670
Fax: (44) 131-650-5379
(C) Nature Genetics press release.
Message posted by: Trevor M. D'Souza
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