Evaluation: Genetic Explanation of Anorexia Nervosa

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A level (Clinical Psychology) Psychology Mapa Mental sobre Evaluation: Genetic Explanation of Anorexia Nervosa, creado por Katie Greensted el 02/06/2019.
Katie Greensted
Mapa Mental por Katie Greensted, actualizado hace más de 1 año
Katie Greensted
Creado por Katie Greensted hace más de 5 años
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Evaluation: Genetic Explanation of Anorexia Nervosa
  1. Twin studies can be used to assess the impacts of genes on the development of anorexia. Mz twins share 100% of their genes; Dz twins share 50%. They both share 100% of their environment. If Mz twins show a higher concordance rate than Dz twins, then this suggests that some part of the disorder is genetic.
    1. Holland et al found a 56% concordance rate in Mz twins and a 5% concordance rate in Dz twins. This suggests the more genetically similar you are to an individual with anorexia, the more likely you are to develop it.
      1. However, as Mz twins share 100% of their genes, a 100% concordance rate would be expected if the cause of the disorder was purely biological. This suggests that there are potentially some environmental factors influencing the development of anorexia. This could link to the diathesis stress model which suggests that some genes are triggered by environmental factors.
    2. Family studies can be used to estimate the percentage of any difference between family members or twins that is due to genes. If genes are an explanation of anorexia, then the frequency of AN in the relatives of someone with the disorder should be higher than the general population.
      1. Strober et al found that in first degree relatives of people with an eating disorder in the family, anorexia was 11.3% more prevalent. This suggests that anorexia is genetic to some extent as it is more likely to occur in people who have it in the family.
        1. However, family studies do not separate nature from nurture so we are unable to tell if these results are influenced by environmental factors. For example, Chadda found that family interaction patterns influenced the weight loss of a 13 year old as her weight loss was being reinforced by her parents.
      2. People with anorexia may inherit genes that contribute to the development of the disorder, but the question remains: how do genes affect behaviour? One possibility is is that they influence the activity of the brain's neurotransmitter systems.
        1. The DAT1 gene is said to play a role in anorexia. The gene codes for a protein which regulates the transport of dopamine between the neon and the synapse. A dysfunction with this gene may lead to a disruption of this process and a dysfunction of the brain's reward system, therefore imparting motivation towards eating.
          1. This raises a question about whether the cause of anorexia is a genetic issue or a neurotransmitter issue.
          2. The 5-HTR2A gene has been linked to anorexia and codes for the 5-HT2A receptor. A mutation in this gene may affect the structure of these receptors. This will lead to less binding between serotonin and the receptor, meaning that appetite-related information will not be transmitted normally, perhaps leading to a loss of appetite and therefore the individual may stop eating.
            1. Walter and Kaye reviewed several studies and found significantly decreased 5-HT2A activity in the serotonergic system throughout the brains of people with anorexia, suggesting that a problem with those receptors are linked to that disorder.
          3. Genetic studies have tried to identify genetic variations linked to anorexia.
            1. Two genes have be largely linked to anorexia. The EPHX2 gene codes for the enzyme which regulates cholesterol metabolism. It has been found that many people with severe anorexia have abnormally high levels of cholesterol.
              1. However, it is unclear whether the dysfunction of this gene is a cause or a consequence of the disorder, so is not a solid explanation of anorexia.
              2. The ITPR gene has also been linked to anorexia. The gene codes for a protein which codes for a receptor involved in detecting different tastes. It has been suggested that a genetically-determined dysfunction of the taste pathway means that those with the disorder will be indifferent to tastes, and therefore will not be motivated to eat.
                1. Anorexia is a polygenic disorder, so no single gene can explain all the symptoms of anorexia. Therefore any theory that suggests one gene is the cause of this complex disorder risks oversimplifying the explanation.
                2. Relatives not sharing the same home environment still show a higher tendency to develop AN when someone has the disorder in their family than relatives of control participants, This suggests anorexia is at least some part genetic.
                  1. Woodside et al found that compared to the general population, first degree relatives with the disorder are more likely to develop anorexia. This is also true for third degree relatives, but to a lesser extent. This suggests that genetics may cause anorexia to some extent as people sharing genes with people with anorexia are more likely to develop the disorder, even when they do not share the same environment.
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