Genetic explanation + Evaluation

Gottesman and Shields (1966) Twin Study

• Large Scale

• 18% increased likelihood of schizophrenia with DZ twins and 54% with MZ twins

Ripke - Meta analysis

• Meta-analysis on genome wide studies

• 108 separate genetic variations were found to me linked to schizophrenia

• Genes linked to dopamine were linked to this risk

Brown et al - Mutation in parental DNA

• can be due to age, radiation exposure, poison or viral infections

• overall risk of schizophrenia in the general population is 1%

• Fathers under 25, 0.7% risk of schizophrenia in child

• Fathers over 50, 2% risk of schizophrenia in child

Gottesman (1991)

• Children with two schizophrenic parents had a concordance rate of 46%

• Children with one schizophrenic parent had a concordance rate of 9%

• Suggests a genetic link as there was a higher concordance rate when there is a higher genetic similarity

Tienari et al (2000)

• Looked at 164 adoptees whose biological mothers were schizophrenic

• 6.7% also received a schizophrenia diagnosis

• 2.7% of the control adoptees (with non-schizophrenic biological mothers)

• This suggests a genetic link as there was a higher rate of schizophrenia in the biologically similar relatives than when there was no genetic link

(Strength) Supporting evidence

Heston (1966) - 50 adoptees without schizophrenic mothers and 47 with schizophrenic mothers. Adoptees separate on the day of birth.

• 10.6% of adoptees with schizophrenic mothers developed schozophrenia whereas none of the control adoptees developed schizophrenia.

• Strongly suggests a genetic link as the adoptees did not share an environment but did share genetic.

(Strength) Practical applications

• We now know that there is a genetic link for schizophrenia, allowing us to intervene early. E.g if a schizophrenic mother has a child we know that there is an increased risk in the child developing the disorder.

• Genetics only give the predisposition of developing the disorder meaning interventions can be put in place in the child's environment to prevent schizophrenia to being triggered. Preventing schizophrenia will reduce the economic strain on healthcare.

(Limitation) Nature vs Nurture

• A purely genetic explanation does not consider the interaction with the environment. E.g Although we may possess a certain gene, it does not mean it is switched on (this can explain why MZ twins do NOT have a 100% concordance rate in Grossman's study).

• Therefore schizophrenia is more likely to be an interaction between nature and nurture, meaning it can be better explained by the diathesis stress model.

(Limitation) Ignores the role of the family

• E.g Living in a dysfunctional family can increase the likelihood that an individual can develop schizophrenia. It has beewn suggested that a schizophrenogenic mother (cold,rejecting and controlling) which creates a family environment with tension and secrecy can be a CATALYST for SYMPTOMS of schizophrenia.

• Therefore we cannot purely use genetics as an explanation, we also have to consider environmental factors.

(Limitation) Methodology

• Research comparing MZ and DZ twins never find a 100% concordance rate, even if it did we cannot factor out environmental factors.

• Schizophrenia may appear to run in families as MZ twins are more likely to be treated more similar than DZ twins since they look the same. They are also more likely to experience 'identity confusion' (frequently being referred to as the 'twins' than distinct individuals) than DZ twins. Therefore we cannot conclude that the supporting research does definitively show a genetic cause for schizophrenia.