JUNKY GENES

SLIGHT genetic variations may make the difference between a person being
unlikely to abuse heroin and being predisposed to it. Now researchers in
Cincinnati are discovering how small changes in a gene could influence
people's tendency to abuse opiates.

If it exists, the link between genes and addiction is likely to be easier
to pinpoint for opiates such as heroin than for other types of addiction.
This is because, unlike alcohol or cocaine, opium works through only one
molecular gateway in the cell.

Studies have already identified a small variation in the gene for the opium
receptor that appears more often in heroin addicts. Now researchers have
confirmed this finding and have found several new variants of the gene, one
of which appears to protect against drug addiction.

Lei Yu of the University of Cincinnati College of Medicine and colleagues
found that an opium receptor gene variant, A118G, which occurs in 20 per
cent of the population, turns up nearly twice as often in people who have
never been addicted to opiates as it does in addicts. They also found that
a naturally occurring brain opioid binds to the A1 18G receptor three times
more strongly than it does to normal opiate receptors (Proceedings of the
National Academy of Sciences, vol 95, p 9608).

The researchers caution that these results are preliminary and based on
only a small study group. Further work will be necessary to determine how
stronger opiate binding could translate into a protection from addiction,
they say. Yu and his colleagues are enrolling more people in their study
and are checking whether other variants associated with heroin addiction
also change the way opiates bind to the receptor.

"It's tremendously exciting," says Alan Leshner, director of the US
National Institute on Drug Abuse near Washington DC. He says the research
shows the first link between a variation in the biochemical activity of a
protein and a predisposition towards heroin addiction. "This is not yet
vulnerability to addiction but it shows we are looking in the right place,"
he says.