KEY POINTS:
SYDNEY - A genetic test may help to stop hyperactive children being overdosed on psycho-stimulant drugs such as Ritalin, Australian research suggests.
About 50,000 Australian children are prescribed stimulants to treat Attention Deficit Hyperactivity Disorder (ADHD), but problems getting the dose right mean many are initially over-drugged.
Studies in adults with the condition show there is a gene which makes some more sensitive to the medication and prone to the "zombie-like" side-effects of overdose.
But overdose affects children in the same way, making them obsessive, introverted, highly focused and unable to change their attention from one thing to another.
ADHD expert Professor Florence Levy, from the University of New South Wales' school of psychiatry, has called for testing to see if the gene couldhelp to get the dose right for young sufferers.
"It has been very hard to predict how kids will respond to treatment," said Professor Levy.
"Some need high doses and some only very small doses ... so you always get people who get far more than they need until it gets picked up, and that's a real problem."
Stimulant medications for ADHD - methylphenidate, known as Ritalin, and dexamphetamine - work by stimulating dopamine, a chemical that controls several brain functions and relays messages.
International researchers have discovered a gene, called COMT, which controls how much dopamine each person produces.
Adults with one version of the gene produced lower dopamine levels and therefore needed higher doses of the stimulants for the drug to work.
But those with the other version already had high levels and required only very small doses of medication.
"So, essentially the wrong people were being overdosed," said Professor Levy, who has published a review in the Australian and New Zealand Journal of Psychiatry calling for the gene to be studied in children.
"It might just be that we're able to predict how kids will react to the drug in advance, and save them [from these fluctuations]."
SIDE-EFFECTS
Overdoses make children:
* Obsessive.
* Introverted.
* Highly focused.
* Inflexible.
- AAP
