By Jennifer Thomas
WEDNESDAY, Oct. 23 (HealthScoutNews) -- Researchers have taken a major step toward finding the genetic underpinnings for attention deficit hyperactivity disorder (ADHD), a discovery they hope will lead to better diagnosis and treatment.
Interestingly, the chromosomal region implicated in ADHD is the same region that previous research has linked to autism, says study author Susan Smalley, co-director of the Center for Neurobehavioral Genetics at the University of California, Los Angeles.
This suggests the two disorders, though they have different symptoms, could share some of the same underlying genetic risk factors, Smalley says.
"It's an intriguing possibility that there could be a common gene that contributes to both," she says. "I won't be surprised if it's the same gene contributing to both, but I certainly don't know for sure."
The study appears in the October issue of the American Journal of Human Genetics.
Smalley and her colleagues spent five years gathering clinical and genetic data on 203 families who had more than one child with ADHD. Using statistical analysis, the researchers identified a series of molecular markers on a region of chromosome 16 among the siblings with ADHD.
The region on chromosome 16 contains about 150 of the 35,000 genes in the human genome. Pinpointing the exact ADHD gene or genes will take additional research, Smalley says.
"All we've done is narrowed down the search from 35,000 genes," she says. "There are still up to 150 genes it could be. Even to find that one, we still have a lot of work to do."
ADHD is the most commonly diagnosed behavioral disorder in children. Though symptoms vary from child to child, it's often characterized by inattention, hyperactivity, impulsiveness, a failure to follow through or plan ahead, and in some cases difficulty maintaining social relationships.
Autism, while a distinct disorder, has some of the same symptoms. Children with autism have problems relating to others. They also have a tendency to perform repetitive movements and develop an obsessive interest in a single subject.
"Either they hardly talk at all or they talk 'at you,' rather than talking 'with you,'" says Dr. Sarah Spence, medical director of the Autism Genetic Resource Exchange, a gene bank for autism research. "No two kids with autism have exactly the same symptoms."
There are some tantalizing similarities between ADHD and autism, says Spence, who was not involved in the just-published research.
Many parents of autistic children report hyperactivity and inattentiveness in their children, emotional outbursts or tantrums, and impulsive behavior. Ritalin or other stimulants, which are commonly prescribed to treat ADHD, are often used to help autistic children, Spence says.
However, both researchers caution against jumping to conclusions about the genetic similarities.
"It could be that the autism gene is in that group of 150 genes, but it's a completely different gene than the ADHD gene," Spence says.
Not only that, complex disorders such as ADHD and autism are almost surely due to multiple genetic and environmental factors, not a single gene, Smalley says.
Based on their analysis, Smalley and her colleagues estimate the gene or genes on chromosome 16 might account for as much as 30 percent of the genetic cause of ADHD. It's estimated that ADHD is 70 percent to 80 percent genetic, she says.
The hope is that when the exact gene or genes are identified, researchers can then study what role they play in brain functioning and what goes awry in children with ADHD or autism.
From there, they could diagnose the disorders sooner -- and develop better, more effective, treatments, Spence says.
"Once we understand the biology of it better, we can learn to treat it better," she says. "Right now, we're at a bit of a loss for what to do and how to know early on if somebody is going to have ADHD."
New treatments don't just mean medications, Smalley says. Some research has shown environmental factors, including low birth rate and smoking during pregnancy, might put children at risk for ADHD.
Anything from dietary adjustments to finding methods of teaching children with ADHD that are better suited to them could help, she says.