genetics

• genetics- family studies

  Gottesman has a large scale family study showing someone with an aunt with sz has 2% chance of developing it, increasing to 9% if the individual has a sibling and 48% if they are an identical twin. Family members tend to share aspect of their environment as well as many of their genes, so correlation represents both. But family studies still give good support for the importance of genes in sz.
• genetics- adoption studies

  Tienari studied 164 adoptees whos biological mother had been diagnosed with sz, 11 also received a diagnosis of sz, compared to just 4 of the 197 control adoptees (who didn't have a biological sz mother). Investigators concluded that these findings showed that the genetic liabilty to sz has been 'decisively confirmed'.
• genetics- candidate gene

  Early research looked for a single genetic variation in the belief that one faulty gene could explain sz. It appears that a number of different genes are involved, sz is polygenic. The most likely genes would be those coding for neurotrasmitters inc dopamine.
• genetics- candidate gene

  Stephen Ripke et al combined all previous data from genome- wide studies of sz. The genetic make up of 37,000 people with a diagnosis of sz as compared to that of 113,000 controls with 108 separate genetic variations were associated with slightly increased risk of sz. Because different studies have identified different candidate genes is also appears that sz is aetiologically heterogeneous e.g different combinations of factors e.g genetic variation e.g lead to the condition
• Strength is the evidence to suggest that genetics are important in the development of sz. Family studies e.g Gottesman show that the risk increases with genetic similarity to a family member with sz. adoption studies e.g Tienari show that biological children of parents with sz are at a increased risk even if they grow up in an adoptive family. A recent twin study by Rike Hilker et al showed a concordance rate of 33% of identical twins and 7% for non-identical twins. Suggests that pople are more susceptible to developing sz due to their genetic makeup
• Weakness is that there is clear evidence to show that environmental factors increase the risk of developing sz. Biological factors include birth complications and smoking THC-rich cannabis in teenage years. Psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems in general but there is now evidence for a particular link with sz. In a study 67% of people with sz and related psychotic disorders reported at least one childhood trauma as opposed to 38% of a matched group with non-psychotic mental health issues.
• weakness is that there are issues with using twin studies as evidence.

  Its incorrectly assumed that MZ and DZ twins share exactly the same environment, which is not always the case. Joseph argues that its widely accepted that MZ twins are treated more similarly, encounter more similar environmental and experience more 'identity confusion' than DZ twins. suggests that environmental and family backgrounds have a strong influence on the development of sz, not just genetics alone