New research points out that the difference in genes might be responsible for the way patients suffering from attention deficit hyperactivity disorder (ADHD) differ in reacting to medications.
The study, done by the researchers from University of Illinois at Chicago, had found that children with a variant form of a dopamine transporter gene -- a variant known to be associated with ADHD -- responded poorly to one of the most common stimulant medications, methylphenidate. The transporter gene encodes a protein on the nerve cell membrane that helps to clear the neurotransmitter dopamine from the nerve junction.
The researchers had first reported an association of this gene with ADHD 10 years ago. In the new study, they had examined the relationship between the gene and patients' medication response over a four-week period, first on a placebo and then on three increasing dosages of methylphenidate.
The researchers tested 47 children with ADHD between 5 and 16 years old to determine which variant of the dopamine transporter gene they carried. They focused on two specific variants -- called 9R and 10R -- of the transporter gene and evaluated how varying doses of methylphenidate would affect ADHD symptoms, impairment, and stimulant side effects.
The majority of the patients had one or two copies of the 10R variant. Of these children, nearly 60 percent had excellent response to the highest dosage (54 milligrams). In contrast, of the patients with two copies of the 9R variant, none displayed such dramatic improvement.
Results of the current study appear in the July issue of the journal Neuropsychopharmachology.