OCR Psychology A Level Book 2 sample

Genetic explanation of depression Family studies The key research for this topic, Irving Gottesman et al. ’s study on page 28, illustrates the increased risk that children have of developing bipolar disorder if their parents have that, or another, disorder. For example, a child with one parent with bipolar disorder has a 4.4% risk of being diagnosed with the same disorder, compared with a 0.63% risk of diagnosis for the general population. Twin studies Concordance rates for major depression in MZ twins are between 30% and 50%, whereas for DZ twins the corresponding range is 12% to 40% (Smoller and Perlis 2004). The results of twin studies consistently and strongly suggest that major depression has a significant causative genetic component. Adoption studies Relatively few adoption studies have been conducted and their results offer less consistent support of a genetic explanation compared with twin studies. Only a study by Paul Wender et al. (1986) showed clear evidence of genetic effects. They found that the biological relatives of a depressed adoptee were eight times more likely than adoptive relatives to also have depression . Association studies Attempts to identify specific genes involved in depression have focused on the human serotonin transporter gene (hSERT) because of the key role that serotonin plays in the biochemistry of depression. The serotonin transporter of the brain recycles serotonin at the synapse . Its activity is governed by the hSERT gene. Genes come in two different versions (known as alleles ). We inherit one allele from each parent. People who have a pair of short alleles on the hSERT gene are less resilient to stress and more likely to respond to stressful events with depressive reactions. Alan Ogilvie et al. ( 1996) compared the hSERT gene in 39 people with major depression and 193 people from the general population (some of whom had been screened for mental illness). They found a significantly higher occurrence of short alleles in the group with depression. Noreen Goldman et al. (2010) found that those with a shortened allele reacted more negatively to stressful events than those with a normal hSERT gene. Taken together, these results suggest that the hSERT gene could be responsible for the inheritance of depression. Background The medical model Topic 2 Genetic principles Concordance and probands The logic of genetic research is that the more genes two people share, the more similar their behaviour/characteristics should be—if the behaviour/characteristic has a genetic basis. Similarity is measured in terms of the correlation or concordance between any two individuals. So we look at concordance rates . In order to conduct research on the genetic basis of mental illness a researcher has to compare people who are genetically related and does this by identifying people with a disorder (called a proband ) and then assessing relatives of the proband. Family studies One way to study this genetic relationship is to identify probands and then assess members of their family. First degree relatives (e.g. proband and parents, or proband and siblings who share 50% of genes on average ) should have higher concordance than second degree relatives (e.g. proband and grandparents, who share 25% of their genes). Twin studies One method used to discover the extent of genetic influence relative to environmental factors is to use twin studies. A twin study is a kind of quasi-experiment in which we compare concordance rates for identical (monozygotic, MZ) and non- identical (dizygotic, DZ) twins. MZ twins are 100% identical genetically because they develop from one fertilised egg (zygote). DZ twins share, on average, about 50% of their genes (the same as any pair of siblings). Both MZ and DZ twins are assumed to share the same environment with their co-twin so environment is controlled. Adoption studies Adoption studies are another method of determining the relative influences of genes and environment. Probands in this context are individuals who were adopted as children. The biological and adoptive relatives of the proband are identified and assessed for presence of a mental disorder. Genetic factors are involved if concordance rates are higher amongst biological relatives than adoptive relatives. Association studies There are two more recently used approaches. Candidate-gene association studies (CGAS) focus on specific ‘candidate’ genes that individually create a vulnerability for a disorder. Genome- wide association studies (GWAS) look at the entire human genome rather than specific genes. The specification requires that you know the background to the medical model of mental illness. For Topic 2 this is divided into three parts: the biochemical explanation, the genetic explanation and the brain abnormality explanation of mental illness. On this spread we look at the second part, the genetic explanation of mental illness. This spread covers the essential information you will need on background for the exam but you also need to link the background to issues and debates and to the key research. We will look at these links on page 30. The genetic explanation of mental illness Genes inherited from our parents determine many features of our behaviour, appearance, personality and achievements. This can also include our mental health. We would therefore expect the direct relatives of those with mental illness to have a higher likelihood of developing mental illness than those without a relative with the illness. For example, if a parent has a mental illness their offspring (children) would be more likely to develop the disorder. The genetic explanation of mental illness Chapter 1: Issues in mental health 24