Biological Explanation
Addiction Genes.
Genetic Factors
- This can explain why although many people engage in potentially addictive behaviours, not everyone
becomes addicted.
- If genes play a role in the development of addiction, then people who are closely related should be more likely
to share the behaviour.
- David Goldman et al (2005): Addictions are ‘moderately to highly heritable’, ranging from +.39 for
hallucinogens. to +.72 for cocaine.
- Some specific genes, following this, have been implicated in the psychopathology of addiction.
DRD2
- DRD2 is the D2 dopamine receptor gene.
- Individuals with the A1 allele of this gene have fewer receptors in an area of the brain that provides us with a
sense of pleasure in response to normally adaptive behaviours such as eating or sex.
- The lower number of receptors may mean the individual overcompensates by engaging in behaviours which
stimulate the receptors by activating dopamine release in the Mesolimbic pathway.
- David Comings et al (1996): 48.7%. of smokers and ex-smokers carry the A1 variant of DRD2 compared with
25.9% of the general population. It was also found in 50.9% of gambling addicts.
ADH
- ADH and ALDH genes are responsible for how alcohol is metabolised by the body.
- Normally, the body metabolises alcohol into acetaldehyde through the enzyme alcohol dehydrogenase (ADH),
and then acetaldehyde dehydrogenase (ALDH) breaks it down further into acetic acid and water.
- Some variants of the genes decrease the risk of alcoholism, they increase the amount of acetaldehyde in the
body which then results in unpleasant reactions to alcohol such as facial flushing or nausea.
- There are lower rates of alcoholism in East Asia, and this reaction is found in greater numbers in these
populations; suggests that they experience the unpleasant reactions and are less likely to engage in the
behaviour again/excessively and thus are less likely to become addicted.
- Therefore, variations of the ADH gene have also been linked to higher risk levels of alcoholism- individuals
with these variations break down alcohol at a much slower rate and are more likely to drink a greater amount.
- Subsequently they are more likely to become addicted.
- Lower activity variants of ADH genes have been linked with an increased risk of alcoholism in oriental
populations, while ADH4 variants have been found to affect the risk in European populations.
Inheritance Studies
- Prescott and Kendler (1999): Used personal interviews to assess alcohol abuse and dependence among 3,516
twins from male-male pairs born in Virginia between 1940 and 1974.
- Concordance rates were much higher between MZ twins than between DZ twins and they concluded that 48-
58% of the variance in alcohol addiction is genetic.
- Kendler et al (2012): large scale adoption study in Sweden, they found that children who had a biological
parent or sibling with a drug addiction were at significantly higher risk of drug addiction themselves.
- The risk was much higher if there were environmental factors in the adopted family such as criminal activity,
divorce, alcohol problems or death.
- Agrawal and Lynskey (2008): reviewed the previous research into the genetic basis of addiction and found
that the genetic influence of addiction ranged from 30-70%. They also highlighted the importance of the
interplay between genes and the environment.
Other Genes
- Mice without the cannabinoid receptor gene Cnr1 are less responsive to morphine.
- Mice bred to lack the ß2 subunit of nicotinic cholinergic receptors have a reduced reward response to cocaine.
- Non-smokers are more likely than smokers to carry a protective allele of the CYP2A6 gene, which causes
them to feel nausea and dizziness from smoking.
