Biological explanations of Schizophrenia

Question 1

What are the genetic factors of schizophrenia?

Answer 1

Family studies
Candidate genes
The role of mutation

Question 2

What are family studies?

Answer 2

Family studies have confirmed that the risk of schizophrenia increases in line with genetic similarities to a relative with the disorder

Question 3

What did Gottesman find?

Answer 3

• Gottesman carried out a large scale family study
• Someone with an aunt with schizophrenia has a 2% chance of developing it
• Someone with a sibling who has schizophrenia has a 9% chance of developing it
• Someone with an identical twin has a 48% chance of developing schizophrenia
• This represents both environment and genetics as families tend to share the same environment

Question 4

What role do candidate genes have?

Answer 4

• Schizophrenia is polygenic and therefore multiple genes contribute to develop
• these genes most likely code for neurotransmitters including dopamine

Question 5

What did Ripke find?

Answer 5

• Ripke combined all previous data from genome - wide studies of schizophrenia
• The genetic make up of 37,000 people with a diagnosis of schizophrenia was compared to that of 113,000 controls, 108 seperate genetic variations were associated with a slightly increased risk of schizophrenia

Question 6

What is schizophrenia?

Answer 6

• aetiologically heterogeneous = different combinations of factors including genetic variation can lead to the condition
• Polygenic = there are a number of different genes involved in developing schizophrenia. The genes most likely code for neurotransmitters such as dopamine

Question 7

What is the role of mutation?

Answer 7

• Schizophrenia can also have a genetic origin in the absence of a family history of the disorder
• One explanation of this is mutations in parental DNA which can be caused by radiation, poison or a viral infection

Question 8

What is the evidence of the role of mutations?

Answer 8

• Evidence for mutation comes from the positive correlation between paternal age which is associated with the increased risk of sperm mutation and the risk of schizophrenia which increases from around 0.7% with fathers under 25 to over 2% in fathers over 50

Question 9

What are the neural components of schizophrenia?

Answer 9

• The dopamine hypothesis

Question 10

What is the original dopamine hypothesis?

Answer 10

• The original hypothesis was based on the discovery that drugs was used to treat schizophrenia (antipsychiotics, which reduce dopamine) caused symptoms similar to those with low dopamine levels
• Therefore, schizophrenia may be a result of high levels of dopamine (hyperdopaminergia)
• For example an excess of dopamine receptors in pathways from the subcortex to Brocas area may explain specific symptoms like poverty of speech and hallucinations

Question 11

What is the updated version of the dopamine hypothesis?

Answer 11

• Kenneth Davis proposed that the addition of cortical hypodopaminergia which is abnormally low DA in the brains cortex
• Low DA in the prefrontal cortex which is responsible for thinking can explain cognitive problems and negative symptoms of schizophrenia such as avolition and disorganised speech
• It has also been suggested that cortical hypodopaminergia can lead to subcortical hyperdopaminergia
• Current versions of the dopamine hypothesis also try to explain abnormal DA levels in genetic variations and also early expieriences of stress

Question 12

What is a strength of the genetic explanations of schizophrenia?

Answer 12

S = one strength is that there is strong evidence
- Family studies such as Gottesman shows that risk increases with a genetic similarity to a family member with schizophrenia
- Adoption studies such as Tienari 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 showed a concordance rate of 33% of identical twins and 7% for non - identical twins
• This shows that some people are more vulnerable to schizophrenia as a result of their genetic make up

Question 13

What is a limitation of genetic factors?

Answer 13

• One limitation is that there are environmental factors that increase the risk of developing schizophrenia
• These include both biological and psychological influences
• Biological risk factors include birth complications and smoking THC - rich cannabis in teenage years
• Psychological risks include child hood trauma. Morkved reported 67% of people with schizophrenia and other psychotic diorders reported at least one child hood trauma compared ro 38% of a matched group with non - psychotic mental health issues

Question 14

What is a strength of the dopamine hypothesis?

Answer 14

• One strength is that there is evidence for the role of dopamine
• For example, amphetamines increase DA and worsen symptoms of those with schizophrenia
• Antipsychotic drugs that reduce DA also reduce the intensity of symptoms
• Some candidate genes act on the production of DA and DA receptors

Question 15

What is a limitation of the dopamine hypothesis?

Answer 15

• One limitation is that there is evidence for a central role of glutamate
• Post mortem and live scanning studies have consistently found raised levels of the neurotransmitter glutamate in several brain reigons of those with schizophrenia
• in addition , several candidate genes for schizophrenia are believed to be involved in glutamate production