Since one of the primaryfunctions of GABA is to inhibit nerve cells from firing, it plays a keyrole in telling the body to "slow down.". The GABA system thereforeacts as a sort of information filter, preventing the brain frombecoming over-stimulated, the researchers explained.
"Impairing the GABA systemcould overwhelm the brain with sensory information, leading to both thebehavior and the pattern of cell damage that emerges in autism," saidJohn Hussman, Ph.D., a study co-author and president of The HussmanFoundation, one of the groups that funded the study.
The researchers examined 14genes that encode portions of the GABA receptor in 470 Caucasianfamilies. Of those families, 266 included more than one person withautism and 204 included one autistic individual. The team tested forassociations between particular gene variants and the disease. Theyalso applied sophisticated statistical methods designed to zero in onthe effects of particular gene combinations.
The researchers found that oneof the GABA receptor genes, GABRA4, is involved in the origin ofautism. Moreover, they report, GABRA4 appears to increase autism riskthrough its interaction with a second GABA gene, GABRB1.
"This is a key finding for ourunderstanding of the complexity of interactions that underlie autism,"Pericak-Vance said. "We can now apply the analytical approach to othergenes that may play a role in the disease." Such findings mayultimately yield a method to screen for individuals at high risk forthe disease, she added.
"The new findings offerimportant new information for families affected by autism about thecomplexity of the disease," said clinical psychologist Michael Cuccaro,Ph.D., a study co-author also of the Duke Center for Human Genetics.
Furthermore, he added, existingmedications already target the GABA system, including diazepam(Valiumฎ) and some anti-epileptic drugs. "As we begin to understand theGABA system as it relates to the neurological underpinnings of autism,we may advance toward new therapies."
Collaborators on the studyinclude D.Q. Ma, P.L. Whithead, M.M. Menold, E.R. Martin, A.E.Ashley-Koch, G.R. DeLong and J.R. Gilbert, all of Duke; H. Mei of NorthCarolina State University; M.D. Ritchie of Vanderbilt University; andH.H. Wright, Ruth Abramson of University of South Carolina.
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