Because elevated blood levels of the neurotransmitter serotonin have long been associated with this disorder, the researchers focused on the genes that regulate the production and function of this powerful chemical messenger. They zeroed in on the serotonin transporter gene (HTT), which codes for a protein that re-absorbs serotonin into the nerve cell after it has been released.
Although the researchers found no change in the coding region of the gene, they did find that autistic children were much more likely to have inherited a shortened form of the gene’s promoter — the DNA sequence that serves as the “on ramp” for the cellular machinery that will express the gene.
A previous clinical study, led by Cook and published in 1992, also points to this protein. Cook and colleagues demonstrated that drugs, such as Prozac (fluoxetine), that inhibit serotonin transport, can reduce the repetitive behaviors exhibited by some children with autism.
Several research teams, studying different groups of patients, are already trying to replicate the team’s discovery of a link between autism and the HTT promoter.