Genetic profile may clarify ADHD drug response

A study explains why some children with the disease don't respond to treatment and may lead to more tailored prescribing.

By Victoria Stagg Elliott, AMNews staff. Sept. 26, 2005.

The fact that some children with attention-deficit/hyperactivity disorder do not respond to the medications that are most commonly prescribed for the condition could be blamed on their genes, according to a study published in the July issue of Neuropsychopharmacology.

Researchers tested nearly 50 children for variations in the 3'-untranslated region of the dopamine transporter gene and changed medication dosages over a four-week period. Those who were homozygous for the less common 9-repeat DAT1 VNTR sequence were far less likely to respond to methylphenidate, a stimulant that is often the first line of treatment for ADHD. They were also less likely to improve as dosages were increased.

"This is an exciting finding, because ADHD is such a common disorder, and it's often difficult to know how patients will respond to ADHD medications," said Mark Stein, PhD, principal investigator and director of the Hyperactivity, Attention and Learning Problems Clinic at the University of Illinois, Chicago.

This finding could lead to genetic testing before prescribing to reduce the amount of time a patient spends taking a drug that is not likely to be effective, the authors said. This is particularly key for ADHD, since it may be weeks before it becomes apparent that the drugs are not working.

"There has always been an art to choosing and titrating medications for ADHD," Dr. Stein said. "It would be tremendous if we could scientifically predict medication response or nonresponse prior to treatment."