Common gene variation involved in regulating serotonin and norepinephrine in the brain may be the reason behind problem behaviors among people with developmental and intellectual disabilities.
"Problem behaviors in these populations account for billions of dollars in intervention costs each year, but nearly all of these interventions occur after the fact. This research suggests one way we might predict which individuals are at risk of being aggressive and destructive and provide treatment before problems occur," Craig Kennedy, a co-author of the study and professor of special education at Vanderbilt University's Peabody College of education and human development, said.
Published in the American Journal on Intellectual and Developmental Disabilities, the study focused specifically on aggression, self-injury, or property destruction.
The researchers set out to determine whether there was a genetic underpinning for these behaviors, and focused on the gene that encodes monoamine oxidize A (MAOA).
MAOA is involved in the regulation of the neurotransmitter serotonin, which is linked to appetite and mood, and the neurotransmitter and hormone norepinephrine, which is linked to the fight-or-flight response.
Studies conducted in the past have shown that variations in MAOA are linked to violent behavior.
"We found that a common variant of the MAOA gene was strongly associated with problem behaviors in adults with developmental and / or intellectual disabilities," Kennedy said.
The researchers divided 105 white men between the ages of 18 and 50 into three groups: those with developmental/intellectual disabilities and a history of more than 10 years of problem behavior, those with the disabilities but without problem behavior, and a typically developing control group.
They say that only white men were sampled because the MAOA gene is linked to the X chromosome, and also is shown to vary by ethnicity.
Forty-three percent of those with developmental/intellectual disabilities and behavior problems had the gene variant, compared to 20 percent of the same group with no behavior issues and 20 percent of a typically developing control group.
The same MAOA variation has also been linked to autism in children, autism severity and communication problems.
The researchers suggest that problem behaviors linked to this variation may explain increased autism severity in individuals with it.
However, it is not linked to behavior problems in individuals with fragile X syndrome, pointing to the need for further research on genetic and other contributors to problem behavior in individuals with different developmental disabilities.