Explanations of anorexia - Genetics Flashcards
What is a gene?
A gene contains a set of instructions and is a carrier of information. Genes are made up of DNA which are responsible for protein synthesis which influences our development.
How can we test genes?
Twin studies and adoption studies investigate the effects of nature or nurture on behaviour. Concordance rates tells us the percentage of cases where the behaviour occurs in both twins, rather than just one which suggests a genetic influence.
What do twin studies suggest?
Kipman et al found that 46.2% of 106 Mz twins were concordant for the disorder and 7.1% of 56 Dz twins were concordant.
Fairburn and Harrisons findings show a concordance rate of about 55% for Mz twins and 5% for Dz twins for anorexia.
What does using family studies do?
Using family and twin studies mean a heritability estimate can be made, which involves estimating the percentage of any difference between family members or twins that is due to genes (leaving the rest to environmental causes and factors)
What do family studies suggest?
Wade et al found that perfectionism, and sensitivity to praise and reward were linked to anorexia.
Bachner- Melin found that three of the genes implicated in AN are also associated with perfectionist personality traits.
Taq1 allele
Associated with alcohol and drug abuse is also present in those with eating disorders (Nisoli et al). The DNAs coding determine distinct traits that can be passed from parents to offspring.
EPHX2 gene
Codes for an enzyme that regulates cholesterol metabolism which has links to serotonin which is associated with anxiety and depression when levels are low. It has links to parts of them brain for eating (hypothalamus) which regulates the feeling of hunger and the amygdala the fear response.
ITPR3 gene
Codes for a protein involved in detecting the taste of food, such as bitter and sweet. If this gene is faulty in those with AN, it could mean they are unable to use taste as a motivator to eat.
Genes and dopamine
Have been linked to the reward system. Reward processing is altered in individuals with AN, even in situations that do not involve food or weight related cues. Individuals failed to differentiate between gaining and losing money in gambling. Therefore, they do not feel rewards when eating food.
DAT1
Gene linked to the dopamine rewards. If a mutation occurs, dopamine activity is disrupted and becomes dysregulated which causes a lack of motivation and satisfaction that others would normally get after eating.
5-HTR2A
Has been found to explain reduced serotonin activity which disrupts neutral information about appetite, explaining why those with AN can go longer without eating.
Scott Van Zealand 2013
Looked at genetic variants associated with development of AN. He found that not one gene variant worked in isolation to explain the cause of AN. ITPR3 was linked to taste of food and EPHX2 was linked to the thalamus and cholesterol. Therefore, genes may increase the risk of AN but were not a direct cause.
Strength - twin studies
Mz twins share 100% of their DNA so if both twins have AN then it is clear that there is a strong genetic link
Weakness - concordance rates
There can be no establishment of cause and effect due to the lack of comparison. Therefore, we don’t know whether genes cause anorexia or whether anorexia causes this change in genes.
Strength - adoption studies
Can help understanding the role of the environment which in some cases can be a confounding variable. By studying adopted participants, in comparison, to their birth parents. If they both have AN, this confirms the genetic link between them.
