Scientists have identified the first gene that may contribute to autism, a type of mental retardation long thought to run in families. The finding, described in next month's issue of Molecular Psychiatry, suggests that autistic children are more likely to inherit a shortened form of the gene, which was already known to help regulate a key brain chemical called serotonin.
Serotonin, a chemical signal released when a neuron fires, has been suspected for over 30 years to play a role in autism. The strongest clue was the discovery that antidepressant drugs like fluoxetine (Prozac) relieve some of the symptoms of autism, such as aggression, fear, and repetitive, ritualistic behaviors. These drugs inhibit the reabsorption of serotonin, making it available longer for transmitting signals between neurons. Ed Cook, a psychiatrist at the University of Chicago Medical Center, reasoned that a gene that regulates serotonin levels might be involved in autism.
Cook and his colleagues examined 86 autistic children and their parents. They found that the autistic children were significantly more likely to have inherited the short version of the gene than simple chance would predict, a finding Cook calls "counterintuitive." That's because the short version should prevent production of a protein that reabsorbs serotonin, leading to higher-than-normal serotonin levels, the opposite of what is expected.
Although seemingly paradoxical, the finding is "potentially enormously important," says Yale University psychiatric geneticist Joel Gelernter. He suggests that in the course of development the body could find ways to compensate for a surplus of serotonin. Cook adds that the short form of the gene is only one factor in the disorder, as it occurs in 16% of the general population, while less than 0.1% is afflicted with autism.