STUDY LINKS GENETICS AND ADDICTION

Drug addiction has become a pervasive and pernicious problem, not
simply because of the wide availability of drugs, but also because
nearly everyone inherits a vulnerability for addiction to
mind-altering chemicals, according to new research.

Just as certain genes make some people more prone to heart disease,
cancer or Alzheimer's disease, scientists now believe that other genes
may make them more susceptible to becoming addicted to heroin,
marijuana or other compounds that affect the brain's natural reward
system.

``It appears that the genetic vulnerability for substance and alcohol
abuse is fairly general in our society,'' says Dr. David Goldman,
chief of neuro-genetics at the U.S. National Institute on Alcohol
Abuse and Alcoholism.

In underscoring the roles that genes and environment play in causing
addiction, the new findings open the possibility of developing the
first effective prevention and treatment strategies for drug abuse.

The findings reveal the inherited biology that turns some people into
alcoholics and debunk long-held beliefs, such as the notion that
marijuana use puts an individual on the slippery slope to cocaine or
heroin use.

Western cultures tend to view addiction as a sin to be condemned or as
a disease to be treated, Goldman says.

``The fact that we have failed too often with either approach suggests
that a better understanding of the origins of addiction could be
useful to help people make better decisions,'' he says.

A study of identical and fraternal twins found that, in general,
genetic influences account for one-third of addiction, family another
third, and peers, friends and co-workers the remaining third.

But all types of addiction are not equal when it comes to the impact
of genes.

The study, which appears in the Archives Of General Psychiatry, found
that genes accounted for more than half of the risk of heroin
addiction, but only 26 per cent of the addiction to
psychedelics.

The biggest factor influencing addiction to psychedelics is the
non-family environment, including friends, schoolmates and co-workers,
which accounts for 53 per cent.

For marijuana addiction, the non-family environment has the biggest
influence, accounting for 38 per cent, while genes account for 33 per
cent.

``Some of these addictions - for example, alcohol and opioid abuse -
are more heritable than susceptibility to coronary artery disease or
obesity,'' Goldman says.

Although addiction-predisposing genes are not yet known, finding them
has become a major goal of the U.S. National Institute on Drug Abuse.
Early success by researchers in linking some genes to alcoholism has
convinced the institute to do the same thing for addiction genes.

The ability to diagnose genes that make a person more susceptible to
specific addictions could result in lifestyle changes to prevent
addiction or the development of medicines that block the individual
action of each drug of abuse.

``Drug addictions join a series of other conditions - for example,
lung cancer, cardiovascular disease, acquired immunodeficiency
syndrome and alcoholism - that are recognized as common, complex,
genetically influenced diseases,'' Goldman says.

``Each of these disorders can be profoundly influenced both by
inherited genes and by such life choices as smoking, diet, exercise,
condom use and abstinence from alcohol.''

The study, headed by Harvard's Dr. Ming Tsuang, also overturns the old
belief that the use of less-addictive drugs such as marijuana, sets
people on the path to becoming hooked on cocaine or heroin.

While some people abuse every drug they can, because these drugs
affect a major chemical path in their reward system, others have genes
that make them addicted to one type of drug that affects only a very
specific part of the reward mechanism.

``There are genetic effects that make some people predisposed to
substance abuse,'' says Dr. Jack Goldberg of the University of
Illinois at Chicago School of Public Health.

``It doesn't mean that addiction is predetermined by genes. It just
means that some of us are more susceptible than others to abusing
drugs if we try them,'' says Goldberg, who participated in the study.

``If you're not genetically predisposed to drug abuse, but are in an
environment where everyone uses drugs, and you do too, you might
become addicted.''

Abused drugs tend to alter levels of natural chemicals called
neurotransmitters, such as serotonin and dopamine, which are involved
in impulse control and the ability of the brain's reward system to
dole out sensations ranging from pleasure to euphoria.

``Nobody gets addicted the first time they use a drug; that's a
myth,'' says Dr. Alan Leshner, director of the drug abuse institute.
``But people do become addicted at different rates. The problem is
that you as an individual have no idea how susceptible you are to
being addicted.

``At its core, addiction is about changed brains. We need to be
looking at genes to see whose brain is more or less susceptible to
being changed.''

Researchers recently found a gene that is linked to antisocial
alcoholism. It is a mutant form of a gene known as HTR1B, which lowers
levels of serotonin and increases the risk of impulsive aggression.

The mutant gene was discovered through genetic analysis of Finnish
alcoholic criminal offenders and a Southwest American Indian tribe
with a high rate of alcoholism.

``These drugs talk directly to the brain in a way a therapist never
can,'' Goldman says. ``Once somebody becomes addicted to a drug, it
appears that the brain is forever changed. They have a greater
vulnerability for relapse.''

Discovering the genes that predispose to addiction will help
scientists track chemical pathways in the brain, allowing them to
devise counter-measures to block a drug's ability to cause a ``high.''
Learning what behaviours in families and among friends induce people
to try drugs and to abuse them will also help to derail environmental
risks.