Addictive Behaviours - Biological Explanations: Genes

Question 1

How could we find out if addictive behaviours have a genetic cause?

Answer 1

• see if it runs in family (hereditary), could do twin studies
• problem with this is that of course they share the same genes, but they also share the same ENVIRONMENT —> can we take away this confounding variable?
• so we use adoption studies

Question 2

What do twin studies assess

Answer 2

The patterns + correlations between monozygotic (identical) and dizygotic (non-identical) twins

Question 3

What is heritability

Answer 3

• statistical concept (represented as h3) — describes how much of the variation in a given trait can be attributed to genetic variation.
• Heritability estimates range from zero to one.
• close to zero = almost all of the variability in a trait among people is due to environmental factors, with very little influence from genetic differences.
• close to one = almost all of the variability in a trait comes from genetic differences, with very little contribution from environmental factors.

Question 4

Which research study shows addiction as heritable

Answer 4

• Goldman et al (2005)
• a review of a large amount of data from numerous twin studies
• found that addiction was moderately to highly heritable
• The lowest heritability rate being for hallucinogens at +0.39 to a high of +0.72 for cocaine.

Question 5

How does Goldman et al (2005) support the genetic explanation of addiction

Answer 5

• the high heritability rates suggests that genetics explain some variation in some addictive behaviours (such as hallucinogens)
• but explains alot of variation in other additive behaviours, e.g. cocaine as 0.72 is close to 1

Question 6

Twin studies are also used to offer support for the role of genetics by
assessing….

Answer 6

Concordance rates

Question 7

What is a concordance rate

Answer 7

• concordance rate is a number, expressed as a percentage, which shows the degree of similarity between two people on a particular trait.
• A low number would suggest little similarity while a higher number suggests higher similarity.
• When considering if a trait is genetic the concordance rate between twins can be assessed.
• A high concordance rate between people who are genetically similar (such as twins) may imply that the trait (at least in some part) is determined by genes.
• Although a high concordance rate between twins for a trait can’t say that the trait is determined by genetics alone it can give us an indication, especially if the concordance rates for a trait are compared between monozygotic (identical) and dizygotic (fraternal) twins.

Question 8

What is the difference between monozygotic and dizygotic twins and how do they vary in terms of genetic similarity to their twin?

Answer 8

• MZ: the fertilised egg splits into 2 = 100% identical in their genetics
• DZ: 2 eggs are fertilised at the same time = share roughly 50% of their genetics

Question 9

Why would it be useful to compare the concordance rate for addiction between monozygotic and dizygotic twins?

Answer 9

• because MZ share 100% of genetics, if they have a higher concordance rate than DZ (who don’t share as much genetic similarity) ——> suggests the addictive behaviour is (in part) determined by genes
• evidence is even stronger if MZ are raised apart (they’ve not shared the same environment)
• HOWEVER = doesn’t prove only genetics are responsible

Question 10

the concordance rate for addiction in monozygotic twins is less than 100% what does this tell us?

Answer 10

It’s the environment playing a role in the addictive behaviour

Question 11

Which research evidence supports MZ DZ explanation

Answer 11

• Kendler and Prescott (1998) used telephone interviews to assess a lifetime history of use, abuse and dependence on cocaine among 1935 twins from female-female pairs including MZ and DZ twins.
• The concordance rate for having used cocaine was 54% for MZ and 42% for DZ twins.
• The concordance rate for dependence however, for MZ twins was 35% and for DZ twins was 0%, a substantial difference.
• supports because they found a higher concordance rate for cocaine dependence in MZ than DZ. Because MZ are identical in genetics —> suggests strong genetic component in cocaine dependence

Question 12

What are the genes associated with addiction

Answer 12

• DRD2 ‘A1’ variant
• ADH and ADLH genes

Question 13

In the context of addiction, what is the DRD2 gene

Answer 13

• the DRD2 gene is a protein coding gene (located on chromosome 11) that is associated with the synthesis (production) of the dopamine receptor D2 (the major dopamine receptor in the brain) and therefore is involved in the regulation of dopamine transmission.
• Mutations in this gene can inhibit dopamine production and activity.

Question 14

What does the DRD2 variant “A1” cause to happen and what effect does this have on behaviour

Answer 14

• when ‘A1’ allele (variant) is present the individual is found to have a reduced number of dopamine receptors
• Because dopamine gives us a sense of pleasure from things such as food, sex, etc = less receptors = less activation = less pleasure
• so individual tries to compensate for this through overstimulation (by doing these addictive behaviours that increase dopamine release)

Question 15

What is the research study that supports the DRD2 “A1” variant playing a role in addictive behaviours

Answer 15

• Comings et al’s (1996)
• studied over 300 non-Hispanic Caucasian participants across the US who smoked at least one pack a day and analysed their blood samples for the A1 variant of the DRD2 gene.
• They did the same for over 200 non-Hispanic Caucasian participants who were pathological gamblers (assessed by questionnaire).
• found 48.7% of smokers and ex-smokers carried the “A1” allele variant, compared with 25.9% of the general population
• similar results found for the gamblers, 50.9% carrying the “A1” allele variant in comparison to 25.9% of non addicts
• supports by showing the association the A1 allele has to both substance and behavioural addictions

Question 16

What are the ADH and ADLH genes responsible for

Answer 16

• the metabolism of alcohol.

Question 17

Why do certain variants of the ADH and ADLH genes decrease the risk of alcoholism?

Answer 17

• some variants lead to increase of acetaldehyde = causing unpleasant facial flushing and nausea
• 2 variants:
  1) ADH 1B: Causing alcohol to metabolise more quickly, causing a build up of the unpleasant acetaldehyde
  2) ALDH 2: causes acetaldehyde to metabolise more slowly cause a build up of aceteldehyde

Question 18

What is the evidence to support the ADH and ALDH variants decreasing the risk of alcoholism

Answer 18

• East Asian populations are found to have a higher concentration of people with this gene variant
• There’s is also typically lower rates of alcoholism in these population
• suggests that the unpleasant side effects of the increased acetaldehyde makes people less likely to drink alcohol and therefore less likely to become addicted

Question 19

How do other variants of the ADH and ALDH gene increase the risk of alcoholism?

Answer 19

• individuals with these variants might breakdown alcohol much slower so there’s less of a buildup of acetaldehyde so less of an unpleasant side effect
• so they drink more and are more likely to become addicted

Question 20

How is variants of ADH and ALDH variants increasing risk of alcoholism supported by research by Edenberg et al (2006) in European populations?

Answer 20

• the ADH4 variant of the ADH gene found to be associated with increased risk of alcoholism in European populations
• (scientists don’t know how it effects alcohol metabolism)

Question 21

When evaluating this explanation, what points can you make?

Answer 21

:(
- reductionist: social and cultural factors
- methodological issues with supporting research: i.e. self reports
- no cause and effect
- using non-human animal studies

:)
- very scientific
- Determinism: gets rid of harmful stigma
- useful

Question 22

Evaluate the explanation for being reductionist

Answer 22

P: The genetic explanation for addiction can be seen as reductionist because of how oversimplified it is, and how it overlooks the role of social factors (such as peer pressure)
E: Boardman et al (2008): studied siblings and twin pairs and found that although there was a strong genetic component in the onset of smoking behaviour, the rate of daily smoking varied across the different schools in the sample. The heritability rate was found to be highest in schools where the most popular students were smokers
E: suggesting that that whether the genetic predisposition to smoke is expressed is influenced by social factors.
L: By ignoring the interaction of social and biological factors, we might miss a complete explanation of addiction (i.e. is able to explain all 3 stages, initiation, maintenance and relapse).
C: This interaction between the environment and genes is further shown through the diathesis-stress model (addiction only develops once genetic predisposition is triggered by an environmental stressor. E.g. Kaufman et al (2007) found the serotonin transporter gene (5HTT) that’s linked to alcoholism to interact very closely with environmental factors, such as maltreatment in childhood

Question 23

Evaluate the explanation for having methodological problems with supporting research

Answer 23

P: It has been argued that some supporting evidence has methodological issues, which ultimately questions the validity of the explanation
E: Kendler and Prescott (1998) used telephone interviews to assess lifetime cocaine use and dependence. This is a problem as the information given is unlikely to be accurate for 2 reasons. First, it relies on the accuracy of their memory of use over their entire lifetime. Secondly social desirability bias is likely to play a role if certain individuals feel uncomfortable giving out information about their use (perhaps playing it down due to embarrassment because of how socially sensitive it is).
T: this is a problem because if any data collected is invalid, then any conclusions drawn about concordance is also invalid
C: There isn’t an ethical way to gather this sort of data other than interviewing individuals who already have used cocaine or have cocaine dependency. It would be highly unethical to induce a cocaine addiction

Question 24

Evaluate the explanation for being scientific

Answer 24

P: some of the methods used are very scientific in their nature
E: Blood/saliva/hair/cheek swabs can be used for genetic testing. There are several types of molecular testing, some looking for specific gene variants and others at the sequence of an organisms whole genome. For example, Comings et al used blood samples and molecular testing to find the A1 variant of the DRD2 gene in smokers and gamblers. Using these methods, he was able to verify that 48.7% of smokers and ex-smokers carried the “A1” allele variant, compared with 25.9% of the general population.
T: These test are an objective measurement conducted by experts and are therefore high in reliability and validity = increasing the validity of the explanation
C: Some may argue that because research methods rely on scientific technology which is conducted in a lab, it therefore lacks environmental validity. By removing participants out of the ‘normal’ social and environmental contexts, it may remove significant factors that contribute to their addiction. Therefore decreasing the validity of any supporting research into the role of genes that is set in a lab

Question 25

Evaluate the explanation for not investigating causal relationships

Answer 25

P: research into concordance rates doesn’t test a cause or effect relationship
E: the concept of epigenetics may be an issue when interpreting the concordance rates from research such as Kendler and Prescott (1998) because concordance doesn’t equal causation. We can’t be sure if addiction is caused by genes alone, environment alone, or even an interaction of the two (i.e. environmental factors effecting gene expression (epigenetics))
T: Therefore if the research only shows association rather than causation, we have to be very careful when drawing conclusions about genetics being the only factor. With research into epigenetics becoming so prominent in modern day society, it seems highly unlikely that addiction is only down to one sole factor. This therefore questions the entire validity of the explanation

Question 26

Evaluate the explanation using supporting evidence from non-human animal studies

Answer 26

P: This explanation is heavily supported by animal studies when there are certain experiments that would be deemed unethical to carry out if done on humans
E: Li et al (1993) carried out research into selectively breeding rats to develop ‘alcohol preferring’ rats. Found that rats that were bred to prefer alcohol exhibited behaviors similar to human addiction, such as seeking alcohol even when it was difficult to obtain. Demonstrating that genetic predisposition played a major role in their addiction to alcohol
T: This selective breeding for addictive traits in humans and forcing them to consume alcohol with the aim to create alcohol dependency would be highly unethical. Considering that humans share 85% of genes with mice, it makes it possible to generalise such important findings from research such as this to humans
C: However, animals do not share the same cultural/social influences as humans, so how a gene variant influences addictive behaviour in animals may not be the same for humans. It is also presents a challenge for research behaviour addictions such as gambling (can’t make mouse play on slots machine with same stakes as a human)

Question 27

Evaluate the genetics explanation for being deterministic

Answer 27

P: the explanation leans heavily into biological determinism, as it is the gene variants that cause the addiction
E: This belief can discourage efforts to seek help or pursue recovery, as they feel powerless to change their behaviour. A study by Lebowitz, Ahn, and Nolen-Hoeksema (2013) found that when individuals attribute their mental health issues (including addiction) to genetics, they are less likely to believe in the effectiveness of therapy or self-driven change, which could lead to worsening conditions or a failure to pursue recovery .
T: Therefore, emphasising genetic determinism may be harmful to patients and could potentially worsen addictions
C: Alternatively other may say that understanding substance use disorders as chronic, treatable conditions, rather than moral failings, can lead to more supportive environments. This view may reduce feelings of shame or guilt in those suffering from addiction, encouraging them to pursue recovery programs and medical assistance

Question 28

Evaluate the usefulness of genetic explanations of addiction

Answer 28

P: It can be very useful understanding the genetic component of addiction when it comes to ‘pharmacogenetics’ which is the investigation into how genetics can effect and individuals response to medicines
E: In relation to addiction it may help select appropriate treatments. Anton et al (2008) found the drug Naltrexone (used to treat alcoholism) works more efficiently in those with a specific gene mutation, they had fewer relapses and higher abstinence than those without the variant
T: If we take a genetic explanation for addiction and investigate which genes/gene variants seem to be linked to certain addictions, it may be possible to tailor drug treatments more effectively based on individual genetics. This proves the genetic explanation to be highly useful