Addiction: Biological explanation; genes

Question 1

What are addiction genes?

Answer 1

• in addition to the role of neurotransmitters and brain processes as explained. the biological approach also suggests that genetics plays a role in explaining why many people engage in behaviours that may be addictive, as not everyone that engages in an addictive behaviour becomes an addict.
• Genes may affect how people respond when they try the behaviour in the first place.

Question 2

What genes are associated with addiction? (DRD2)

Answer 2

• many studies have indicated a role for the D2 dopamine receptor gene (DRD2). individuals with A1 variant of this gene have fewer dopamine receptors in an area of the brain that provides us with a sense of pleasure in response to normally adaptive behaviours such as eating and sex (i.e. in the brain’s pleasure centre)
• The lower the number of dopamine receptors in these individuals mean that they try and compensate for this by overstimulation through engaging in addictive behaviours
• David Comings (1996) found that 48.7% of smokers and ex smokers carried the A1 variant of the DRD2 gene compared with 25.9% of the general population.

Question 3

What genes are associated with addiction? (ADH)

Answer 3

• ADH and ADLH genes are responsible for the process of how alcohol is metabolised by the body. Normally, the body metabolises alcohol into acetaldehyde due to an enzyme called alcohol dehydrogenase (ADH). Then another enzyme called acetaldehyde acetadehydrogenase (ALDH) breaks it down further into acetic acid and water.
• there are some variants of the gene ALDH and ADH genes that decrease the risk of alcoholism by increasing acetaldehyde levels in the body. this in turn causes unpleasant reactions to alcohol, such as facial flushing and nausea.
• This reaction is found in larger concentrations among East Asian populations and may help to explain the lower rates of alcoholism in these cultures; individuals find the experience of drinking so unpleasant they do not want to do it again and are therefore less likely to get addicted.

Question 4

Evaluation; difference between initiation and maintenance

Answer 4

• twin studies have been used to demonstrate the influence of genetic factors in addiction.
• Kenneth Kendler and Carol Prescott (1998) interviewed nearly 2000 twins and found that, although environmental and social factors would influence whether a person would initiate cocaine use, whether the person became addicted was more dependent on genetic factors.
• for example, the concordance rate for cocaine initiation was 54% and DZ twins it was 42%. However when looking at concordance rates for the dependence on cocaine, there was a substantial difference between MZ and DZ twins (35% and 0% respectively), suggesting a much greater for genetic factors in addiction rather than the decision to use it.

Question 5

Evaluation; a gene for addiction?

Answer 5

• the relationship between genetics and addiction is more complex that it may first appear.
• as well as the DRD2 and ADH genes, a number of others have been identified.
• for example Shamsideen Ojelade et al. (2015) found that when a gene called rsu1 was not functioning correctly in fruit flies it would lower their sensitivity to alcohol. Brain imaging was then use to test for this in humans, and found that a relationship between this and alcohol dependence. The range of different genes identified means that we cannot simply say that there is a gene for addiction.