Heroin habit linked to gene
by Michael Day
A TENDENCY to abuse heroin can arise partly from your genes, say
researchers in Israel. Experts say that their discovery of a link between a
specific gene mutation and opiate addiction adds weight to the growing
evidence that a handful of key genes play a role in a wide variety of
addictions.
The group, led by Richard Ebstein of the Sarah Herzog
Memorial Hospital in Jerusalem, studied 141 men who were addicted
to heroin. In each of the men the researchers analysed the gene which
produces a receptor molecule, called the D4 receptor, for the brain
chemical dopamine.
The researchers had suspected that the D4 receptor was linked
to opiate addiction because some studies have hinted that an
abnormally long, mutated form of this gene is relatively common in
people who demonstrate impulsive, "novelty seeking" behavioura
trait that is common among drug addicts.
"This appears to be contributing something to drug abuse and
heroin abuse," Ebstein told New Scientist. In this month's issue of
Molecular Psychiatry (vol 2, p 251), his team reports that this
mutation was almost 25 times as common in the 141 addicted men as
in 110 controls: 29 per cent of the addicts had the mutant D4
receptor gene, compared with 12 per cent of the controls.
Studies of this type are controversial because of the possibility
that the genetic trait only occurs in the racial group under investigation,
and might not exist among addicted people in other ethnic populations.
So the authors studied two related but distinct ethnic groups: Israeli
Arabs and Sephardic Jews. They found that the ratio of normal to long
D4 genes in the addicts and controls of both groups was similar.
"This mutation in the D4 receptor has been associated with
alcohol and nicotine abuse, so it's not that surprising that it is linked to
heroin abuse too," says Kenneth Blum of the University of Texas
Health Science Center at Houston, a leading researcher into addiction.
"But it does show that the common genetic factors put people at
greater risk of a variety of addictive behaviours. "
Obviously, genetic factors do not cause addictionthey
merely raise or lower the risk. "The environment has a big role to
play," says Blum. Ebstein and his colleagues note that other, as yet
unidentified genes may also contribute to the risk of addiction. Blum
suspects that mutations in the genes for receptors called D2 and D1
may play a role.