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 L1 retrotransposons are particularly active in the cerebellum, which plays an important role in motor control. Green cells represent neurons with new L1 insertions. (Credit: Courtesy of Dr. Carol Marchetto, Salk Institute for Biological Studies)

ScienceDaily (Nov. 17, 2010) — With few exceptions, jumping genes-restless bits of DNA that can move freely about the genome-are forced to stay put. In patients with Rett syndrome, however, a mutation in the MeCP2 gene mobilizes so-called L1 retrotransposons in brain cells, reshuffling their genomes and possibly contributing to the symptoms of the disease when they find their way into active genes, report researchers at the Salk Institute for Biological Studies.

Their findings, published in the November 18, 2010 issue of the journal Nature, could not only explain how a single mutation can cause the baffling variability of symptoms typical of Rett syndrome but also shed new light on the complexity of molecular events that underlie psychiatric disorders such as autism and schizophrenia.

“This is the first time that we can show a connection between genomic stability and a mental disorder,” says lead author Fred Gage, Ph.D., a professor in the Salk’s Laboratory of Genetics and holder of the Vi and John Adler Chair for Research on Age-Related Neurodegenerative Diseases. “In general genomic mosaicism, generated by L1 retrotransposition, likely requires tight regulation. Epigenetic mechanisms like methlyation are ideally suited for controlling L1 activity.”

“There is certainly a genetic component to Rett syndrome and other psychiatric disorders but it may not be the only thing that’s relevant,” says first author Alysson Muotri, Ph.D., who started the study as a postdoctoral researcher in the Gage lab and now holds an appointment as an assistant professor in the Department of Pediatrics/Cellular and Molecular Medicine at the University of California, San Diego School of Medicine. “Somatic insertions and alterations caused by L1 elements could play a significant but underestimated role because they are hard to detect,” he adds.

Rett syndrome, a rare neurodevelopmental disease, affects mostly girls and is considered one of the autism spectrum disorders. Most babies seems to grow and develop normally at first, but over time, children with Rett syndrome have increasing problems with movement, coordination and communication.

Typical features include loss of speech, stereotypic movements, mental retardation and social-behavioral problems. Although almost all cases are caused by a mutation in the MeCP2 gene, how severely people are affected by the symptoms of Rett syndrome varies widely.

Read in Full:  http://www.sciencedaily.com/releases/2010/11/101117141417.htm



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