Reversal of Symptoms Accomplished in Autism Disorder

Findings of a landmark study showed that symptoms of Rett syndrome (RTT), an autism disorder, were reversed in a genetic mouse model.

The study, led by Adrian Bird, Ph.D., professor of genetics at the University of Edinburgh (UK) and chairman of the Rett Syndrome Research Foundation (RSRF; Cincinnati, OH, USA) scientific advisory board, appears online in the journal Science Express on February 8, 2007.

Rett Syndrome is a severe childhood neurologic disease that is the most physically disabling of the autism spectrum disorders. Caused by mutations in the gene MECP2, RTT affects mostly girls, striking at random in early childhood and destroying speech, normal movement, and functional hand use. Many children become wheelchair bound; those who walk display an abnormal, stiff-legged gait, chaotic breathing patterns, and Parkinson-like tremors are typical. Restoration of fully functional MECP2 over a four-week period eradicated tremors and normalized breathing, mobility and gait in mice that had previously been fully symptomatic and, in some cases, only days away from death.

"Like many other people, we expected that giving MECP2 to mice that were already sick would not work,” said Dr. Bird. "The idea that you could put back an essential component after the damage to the brain is done and recover an apparently normal mouse seemed farfetched, as nerve cells that developed in the absence of a key component were assumed to be irrevocably damaged. The results are gratifyingly clear, though, and must give hope to those who are affected by this distressing disorder.”

MECP2, first identified by Dr. Bird in 1990, is believed to be a protein that regulates the expression of other genes by turning them off at the appropriate time. In 1999, other researchers discovered that RTT is caused by mutations in the MECP2 gene. Mutations in MECP2 are now being seen in some cases of childhood schizophrenia, classic autism, and learning disabilities.

The reversal study was carried out in the Bird lab by research assistant Dr. Jacky Guy. Employing technology known as Cre-lox recombination, she created mouse models in which MECP2 was silenced by insertion of a Stop cassette into the gene, resulting in the neurologic deficits seen in RTT. Silencing could be reversed at will by removing the Stop cassette, thereby reactivating the MECP2 gene. This was achieved by treating the mice with a drug that caused the enzyme Cre to enter the cell nucleus where it could splice out the cassette.

As well as losing overt behavioral defects, the mice also recovered a major electrophysiologic function of the brain. This was determined by measuring LTP (long-term potentiation), which provides a quantifiable measurement of the ability of neurons to respond to stimulation. LTP has long been thought to reflect the cellular basis of learning and memory. Although LTP in RTT mice models was defective, it was restored to normal function by the reversal experiments.

"The reversal of neurological defects, reported in the remarkable article by Guy et al, is surprising because the cause of the symptoms occurred early in development and was expected to be permanent. Of particular note is the recovery of LTP, which is the best current physiological correlate of learning and memory. These findings are very encouraging for those searching for a treatment because they give hope that the symptoms could not only be halted from progressing, but the course of the disease itself may be able to be reversed,” stated Fred Gage, Ph.D. of the Salk Institute of Biological Studies (La Jolla, CA, USA).

"Dr. Bird's astonishing results usher in a new era for Rett Syndrome and other autism spectrum disorders. The reversal experiments provide justification for aggressive exploration of next steps on all fronts, from drug discovery to gene correction. The Rett Syndrome Research Foundation will be focused on a comprehensive effort to identify and speed treatments to the children and adults in dire need of them,” commented Monica Coenraads, co-founder and director of research for RSRF and mother of a young daughter with the disorder.




Related Links:
University of Edinburgh
Rett Syndrome Research Foundation