Biological Explanations - Genetic Basis

Question 1

Family Studies

Answer 1

• Risk of schizophrenia increases in line with genetic similarity to a relative with the disorder – Gottesman’s (1991) large-scale family study
• 48% concordance rate with identical twins, 17% with fraternal twins, 13% with children, 9% with siblings, 6% with parents, 1% for general population
• Family members tend to share aspects of their environment as well as genes, so the correlation represents both – family studies can still give good support for the importance of genes

Question 2

Candidate Genes

Answer 2

• Early research in this area looked for a single genetic variation in the belief that one faulty gene could explain schizophrenia
• However, it appears that a number of different genes are involved (schizophrenia is polygenic)
• Most likely genes would be those coding for neurotransmitters including dopamine

Question 3

Ripke et al (2014)

Answer 3

• Combined all previous data from genome-wide studies (looking at whole human genome, not particular genes)
• The genetic make-up of 37000 people with a diagnosis was compared to that of 113000 controls – 108 separate genetic variations were associated with a slightly increased risk of schizophrenia
• Because different studies identified different candidate genes, it also appears that schizophrenia is aetiologically heterogenous (different combos of factors can lead to the condition)

Question 4

Role Of Mutation

Answer 4

• Schizophrenia can also have a genetic origin in the absence of a family history of the disorder – one explanation for this is mutation in parental DNA which can be caused by radiation, poison, or viral infection
• Evidence for mutation comes from positive correlations between paternal age (associated with increased risk of sperm mutation) and risk of schizophrenia, increasing from around 0.7% with fathers under 25 to 2% in fathers over 50 (Brown et al in 2002)

Question 5

Evaluation - Strong evidence base

Answer 5

• Family studies like Gottesman show that risk increases with genetic similarity to a family member with schizophrenia
• Adoption studies such as 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
• A recent twin study by Hilker et al (2018) showed a concordance rate of 33% for identical twins and 7% for non-identical twins
• Some people are more vulnerable to schizophrenia as a result of their genetic make-up

Question 6

Evaluation - Clear evidence to show that environmental factors (biological and psychological influences) also increase risk of developing schizophrenia

Answer 6

• Biological risk factors include birth complications (Morgan et al in 2017) and smoking THC-rich cannabis in teenage years (Di Forti et al in 2015)
• Psychological risk factors include childhood trauma which leaves people more vulnerable to adult mental health problems – Mørkved et al (2017) found that 67% of people with schizophrenia and related psychotic disorders reported at least one childhood trauma as opposed to 38% of a matched group with non-psychotic mental health issues
• Genetic factors alone cannot provide a complete explanation