Gene Linked To Autism In Families With More Than One Affected Child
Autism spectrum disorders
A version of a gene has been linked to autism in families that have more than one child with the disorder. Inheriting two copies of this version more than doubled a child's risk of developing an autism spectrum disorder, scientists supported by the National Institutes of Health's (NIH) National Institute of Mental Health (NIMH) National Institute on Child Health and Human Development (NICHD) have discovered. In a large sample totaling 1,231 cases, they traced the connection to a tiny variation in the part of the gene that turns it on and off. People with autism spectrum disorders were more likely than others to have inherited this version, which cuts gene expression by half, likely impairing development of parts of the brain implicated in the disorder, report Drs. Daniel Campbell, Pat Levitt, Vanderbilt Kennedy Center at Vanderbilt University, and colleagues, online during the week of the October 16, 2006 in the Proceedings of the National Academy of Sciences.
"This common gene variant likely predisposes for autism in combination with other genes and environmental factors," said Levitt. "It exerts the strongest effect detected thus far among autism candidate genes."
Autism is one of the most heritable mental disorders. If one identical twin has it, so will the other in nearly 9 out of 10 cases. If one sibling has the disorder, the other siblings run a 35-fold greater-than-normal risk of having it. Still, scientists have so far had only mixed success in identifying the genes involved.
While most previous studies had focused on genes expressed in the brain, Levitt's team saw a clue in the fact that some people with autism also have gastrointestinal, immunological or neurological symptoms in addition to behavioral impairments. They focused on a gene that affects such peripheral functions as well as the development of the cortex and cerebellum, brain areas disturbed in autism. Moreover, it is located in a suspect area of chromosome 7 that has been previously linked to autism spectrum disorders.
This MET receptor tyrosine kinase gene codes for a protein that relays signals that turn on a cell's internal machinery and is known to play a key role in both normal and abnormal development, such as cancer metastases (hence its name). Levitt's group and others had earlier found that impairing the receptor's signaling interferes with neuron migration and disrupts neuronal growth in the cortex and similarly shrinks the cerebellum