Risk factors - Genetic vulnerability Flashcards
Key features of the Biological Approach…
Views humans as biological organisms.
Explains human behaviour in terms of physical factors, including…
Genetics – assumes that behaviour is inherited, therefore recognising the process of evolution.
The central nervous system (brain and spinal cord) – explains behaviour in terms of the physical structure and functioning of the brain.
Biochemistry – Chemicals found in the brain (neurotransmitters) and body (hormones) are believed to influence reactions to the environment.
Researchers have conducted the following types of studies to examine genetic influences:
Twin studies – comparing monozygotic (MZ) against dizygotic (DZ) twins
Family studies - looking at the prevalence of addictive behaviours amongst relatives of addicted people (probands)
Adoption studies
Why is it useful to compare MZ and DZ twins?
If a behaviour has a genetic basis, then it should be more prevalent amongst MZ (identical) twins as they share 100% of their genes, whereas DZ (non-identical) twins only share 50% of their genes.
Concordance rate
the probability that a pair of individuals will both have a certain characteristic.
If a behaviour has a purely genetic basis, then the concordance rate should be 100% amongst MZ twins.
Genetic Vulnerability
the idea that someone may be more likely to become an addict because of their genetic make-up (their genotype).
This does not mean that they will definitely develop an addiction but they are more likely to, given the right circumstances.
What circumstances might these be?
Exposure to a substance or the opportunity within their environment to take it.
Therefore, a gene-environment interaction is necessary to bring about addictive behaviour.
Slutske et al. (2010)
studied 2,889 pairs of twins to investigate the role of genetic and environmental factors in the development of gambling addiction, comparing male and female twin pairs.
Both male and female MZ (identical) twins were found to have much higher concordance rates (where both individuals in the pair were pathological gamblers) compared to DZ (non-identical) twin pairs.
Male twin pairs: 49% (MZ) vs. 21% (DZ);
Female twin pairs: 55% (MZ) vs. 21% (DZ)
Therefore, identical twins who were gamblers were more
Blum & Payne (1991):
individuals who are vulnerable to drug addiction suffer from abnormally low levels of dopamine and a decreased ability to activate dopamine receptors in the reward centre of the brain (the nucleus accumbens). This means that anything that increases the amount of dopamine can produce strong feelings of euphoria.
Blum et al. (1990) reported that a particular variant (the A1 variant) of the dopamine receptor (DRD2) gene associated with fewer dopamine receptor sites (resulting in lower levels of dopamine in the brain) occurred with a much higher frequency in the DNA of samples taken from alcoholics compared to non-alcoholics.
Other research has implicated the A1 variant of the DRD2 gene in nicotine dependence, cocaine dependence and addiction to gambling
The Dopamine Receptor GeneThe A1 variant of the DRD2 gene (the ‘reward gene’)
Individuals with this gene may not receive enough stimulation from everyday activities, such as eating and sex. Thus, individuals continue to engage in the addictive behaviour to compensate for the dopamine deficiency and increase levels of the neurotransmitter in the nucleus accumbens.
The DRD2 gene has been associated with alcoholism
(Noble et al., 1991, found 48% of severe alcoholics carry this gene)
The A1 variant of the DRD2 gene has also been linked to smoking addiction:
Comings et al. (1996) found that 48% of 312 smokers (who smoked at least one pack per day, had unsuccessfully attempted to stop smoking and were free of alcohol and other drug dependence) were found to carry the A1 variant compared to 25% of 714 non-smokers (who were also free of drug and alcohol addiction).
Evaluating Genetic Vulnerability as a Risk Factor in the Development of Addiction
Research support: research clearly indicates a genetic vulnerability to addiction e.g. Slutske et al. (2010).
An advantage of the genetic vulnerability explanation of addiction is that it can explain why some people develop addictive behaviour, yet others who have the same environmental experiences and life pressures do not.
No concordance rates in twin studies (among MZ twins) have ever shown 100% concordance, suggesting that genes only predispose an individual to addiction as opposed to being the sole determining factor.
Genetics and the Diathesis-Stress Model
Research suggests that a gene-environment interaction is needed for an addictive behaviour to develop - an individual will not become addicted if they are not exposed to the substance in their environment.
The Diathesis-Stress Model: we inherit a genetic vulnerability for developing an addiction. However, a disorder will only manifest itself if triggered by a life event.
Evaluating Genetic Vulnerability as a Risk Factor in the Development of Addiction
The role of the environment must be considered.
The diathesis-stress model offers an explanation as to how genes interact with the environment.
- Environmental factors which affect the predisposition to addiction include exposure to the drug, availability of the drug, stress, family influence and peers.
The genetic link to addiction varies across substances.
This suggests that the vulnerability is not general, but specific to certain substances.
Therefore, an individual may respond to different substances in different ways, depending on their genetic make-up.
