In fact, a person with autism may have mutations in several of perhaps 20 possible genes. Thus, two people with the disorder might have mutations in two completely different sets of genes. In the past two years, scientists have identified several candidate genes. Some might alter the effects on the brain of neurotransmitters, others might compromise the immune system enough to allow viral infections that may cause autism, and another may influence embryonic development of the nervous system. Among the most promising findings, say experts, are reports that an autism gene may be on the long arm of chromosome 15, near the centromere an indented point that holds the two sides of a chromosome together.
Short duplications cause no apparent harm.
But longer duplications are associated with about a 50 percent risk for autism. Last year, the research team of child psychiatrist Edwin Cook, MD, of the University of Chicago, reported that the autism risk associated with longer duplications appears to come through the mother. In fact, three genes for three GABA receptor subunits all are good candidates because they are associated with seizures and anxiety, which are common among autistic children, Cook says. His team found moderately strong evidence for an association between one GABA subunit and autism about one of every 70 children studied had a chromosome 15 duplication including this gene. Duke University researchers say an autism gene might be a little farther away from chromosome 15 s centromere, just beyond the GABA receptor genes.