AO1 - Biological Explanations Schizophrenia

• The genetic explanation of schizophrenia suggests that innate, inherited characteristics are responsible for the vulnerability in developing the disorder.
• Evidence suggests that the closer the biological relationship, the greater the risk of developing schizophrenia.
• Kendler (1985) has shown that first-degree relatives of those with schizophrenia are 18 times more at risk than the general population.
• Gottesman (2010) found a strong link for schizophrenia between parents and their offspring. The research shows that offspring are 31.7 times more likely to develop schizophrenia when both parents have been diagnosed with it.
• Concordance rates are calculated to show the level of genetic agreement in twin and family studies. The higher the concordance rate, the stronger the genetic link to schizophrenia.
• Varma & Sharma (1993) reported a concordance rate of 35% in first degree relatives of people with schizophrenia, compared to only 9% in a control group.
• Twin studies and family studies are used to show the likelihood of genetic vulnerability in schizophrenia.
• There are two types of twins – identical (monozygotic) and fraternal (dizygotic). MZ twins share 100% of their DNA, whereas DZ twins only share 50% of their DNA.
• Gottesman & Shields (1976) document a concordance rate of 58% in MZ twins and 12% in DZ twins, suggesting a strong genetic link for schizophrenia.
• Gottesman (1991) found that MZ twins have a 48% risk of getting schizophrenia whereas DZ twins have a 17% risk rate. This is evidence that the higher the degree of genetic relativeness, the higher the risk of getting schizophrenia.
• A recent twin study by Hilker et al (2018) found a concordance rate of 33% for identical twins (MZ) and 7% for non-identical twins (DZ).
• Some research into the genetic explanation of schizophrenia aims to identify candidate genes. Early research in this area looked for a single genetic variation in the belief that one faulty gene could explain schizophrenia.
• Recent research claims that a number of different genes are involved in schizophrenia (polygenic).
• Ripke et al (2014) combined previous data from genome wide studies of schizophrenia and found 108 separate genetic variations that were associated with an increased risk of schizophrenia.
• As different studies have identified various candidate genes it appears that schizophrenia is aetiologically heterogeneous.
• Benzel et al (2007) identified three genes associated with schizophrenia. These genes are COMT, DRD4 and AKT1. All have been associated with excess dopamine in specific D2 receptors, leading to acute episodes of psychosis including positive symptoms such as delusions and hallucinations.
• Miyakawa et al (2003) studied DNA from families affected by schizophrenia and found that those with the disorder were more likely to have a defective version of a gene, called PPP3CC which is associated with the production of calcineurin which regulates the immune system.
• Sherrington et al (1988) found a gene located on chromosome 5 which has been linked in a small number of extended families where they have schizophrenia.
• One genetic explanation for schizophrenia is based on a mutation in parental DNA which can be caused by radiation, poison or viral infection.
• Brown et al (2002) found a positive correlation between paternal age and risk of schizophrenia. They suggest a correlation of 0.7% in fathers under 25 and 2% in fathers over 50.
• Adoption studies can show the biological influence of schizophrenia. If adopted children of biological parents with schizophrenia, also develop the disorder it provided support for the genetic explanation.
• Kety et al (1988) found 14% of biological siblings of adoptees were classified as schizophrenic whereas only 2.7% of adoptive siblings were found to be schizophrenic.
• Heston (1966) reported that the offspring of severely schizophrenic mothers who were removed from them during the first 3 days of life still grew up to have schizophrenia at the same rate as those reared by their schizophrenic mothers at home.
• Tienari et al (2004) show that biological children of parents with schizophrenia are at heightened risk even if they grow up in an adoptive family.