Evaluation: Genetic Explanation of Schizophrenia

Evaluation: Genetic Explanation of Schizophrenia

1. Jessica Wright indicated that as many as 700 genes have been linked to schizophrenia (2014), so by now this figure is likely to be in the 1000s.

   • Schizophrenia can appear in the absence of a family history of the disorder, which could suggest that this is due to a mutation in our genes. These changes to genes can result from an environmental factor or an error in cell division. For example, 25% of people with Di George syndrome develop schizophrenia, and this is a condition which is caused by the deletion of genes in chromosome 22.
   • The COMT gene has been linked to schizophrenia, as the link between Sz and the Di George syndrome may be due to a deletion of the COMT gene. These genes provide the instructions for the creation of an enzyme which breaks down neurotransmitters such as dopamine.
   • The DISC 1 gene - people with an abnormality to this gene are 1.4x more likely to develop Sz (Kim et al). This gene codes for GABA, which is a neurotransmitter that regulates others such as dopamine and glutamate.
   • There are similar trends found in a lot of different studies from more than one country, which all support one another's findings. This suggests that the idea that genes play a part in the development of schizophrenia is a reliable explanation.
   • The idea that genes are the primary cause of schizophrenia is extremely reductionist, particularly since concordance rates are less than 100% for Mz twins, suggesting that there is room for environmental influences to 'cause' schizophrenia.
     • The diathesis stress model suggests that behaviour, such as schizophrenic behaviours, comes from in part a genetic predisposition which is the triggered by environmental factors. This could explain why there is not a 100% concordance rate for Mz twins as one may not experience the same environmental trigger and therefore not develop the disorder.
   • There is no clear chromosomal abnormality that is linked to schizophrenia. Although researchers have found many genes which can be linked to symptoms of schizophrenia or predispose someone to Sz, there is no clear link.

2. Family Studies

   • Schizophrenia has been found to have a strong heritable factor. Gottesman's family study into schizophrenia (1991) found that the concordance rate for schizophrenia in the general population was 1%, whereas it was 48% for Mz (identical) twins. This suggests that the greater the degree of genetic relatedness, the higher the risk of developing schizophrenia is.
     • However, the fact that Gottesman's results suggested the concordance rate for Mz twins was only 48% suggests that there must be other factors influencing the development of schizophrenia, otherwise the concordance rate would be 100% in identical twins.
       • Concordance rates in families may be more to do with common rearing patterns or other environmental factors (particularly in Mz twins because they look identical so are treated identically a lot of the time).

3. Twin Studies

   • Researchers use twin studies to investigate the influence of nature and nurture as Mz twins share 100% of their genes whereas Dz twins only share 50%. Gottesman and Shields (1966) found that the concordance rate of Mz twins was 42% compared to Dz twins which was only 9%. Similarly to Gottesman's later family study, this suggests genes do have an influence, however as the figure for Mz twins is not 100%, it is not based on genetics alone.
     • Twin studies often have very small sample sizes and therefore the results have low population validity. This means it is difficult to generalise them to the general population.

4. Adoption studies

   • Adoption studies are used by researchers as it allows them to disentangle genetic and environmental influences.
     • Heston found that the concordance rate in the control group of adoptees (no history of Sz in biological family) was 0%, whereas in the group where the adoptee's biological mother had schizophrenia, the concordance rate was 16%. This suggests there is a biological influence in the development of Sz. This is backed up by Tienara who found similar figures (control = 1%, bio mother with sz = 10%)
       • Fewer than one third of people with Sz have a family history of the disorder, which suggests that there is a complexity in the genes in question and may not be as simple as just inheriting a gene from your parents.