Schizophrenia: Genetic Explanation

Question 1

Why is there a genetic explanation for schizophrenia?

Answer 1

The human genome comprises some 23,000 genes, each with specific instructions about how to build a unique person. And up to 700 of them play a role in schizophrenia (Wright 2014).

Question 2

Why can schizophrenia be called genetic? (heritability, genes, twins)

Answer 2

• Heritability of schizophrenia may be 79% (Hilker et al. 2018)
• Up to 700 genes identified play a role in schizophrenia (Wright 2014)
• If one MZ twin has schizophrenia, the other has a 48% chance of also having it (Gottesman 1991).
  CA : MZ twins share 100% of their DNA, so If it was totally genetic, it would be 100% and not 48%.

Question 3

What role do gene mutations play in schizophrenia?

Answer 3

Schizophrenia can appear without a family history. Mutations can result from an environmental factor or an error in cell division (e.g. deletion or duplication of a DNA strand).

-For example, up to 25% of people with DiGeorge Syndrome develop schizophrenia (this condition is caused by the deletion of 30-40 neighbouring genes in a specific region of chromosome 22).

Question 4

How do specific genes affect schizophrenia? (COMT, DISC1)

Answer 4

COMT Gene
- The link between DiGeorge Syndrome and schizophrenia may be due to deletion of the COMT gene.

• COMT gene creates an enzyme that breaks down neurotransmitters such as dopamine.
• ## Deletion of COMT would mean poor regulation of dopamine levels resulting in schizophrenic symptoms.DISC1 Gene
• People with an abnormality to this gene are 1.4 times more likely to develop schizophrenia than people without (Kim et al. 2012).
• DISC1 creates GABA which regulates glutamate and dopamine in the limbic system.

Question 5

What is a strength of the genetic explanation of schizophrenia? (hint: runs in families)

Answer 5

A strength of the genetic explanation is that there is research showing that schizophrenia runs in families.

Gottesman (1991) showed a 48% concordance rate for MZ twins and 17% for DZ twins.

This greater concordance rate for MZ twins shows that genetics play a role in schizophrenia, as MZ twins share more genes than DZ twins.

Question 6

What is a weakness of the genetic explanation of schizophrenia? (hint: concordance isn’t close to 100%)

Answer 6

A weakness of the genetic explanation is that it is not a complete explanation for schizophrenia.

MZ twins share 100% of their DNA, yet the concordance rates for schizophrenia is only 48% for MZ twins (Gottesman, 1991)

This suggest that the environment plays a significant role in schizophrenia, as the concordance rate would be closer to 100% if it was purely genetic.

Question 7

What is an application of the genetic explanation of schizophrenia? (hint: inform families on heritability)

Answer 7

An application of the genetic explanation is that it has been used in genetic counselling.

When a family member receives a diagnosis of schizophrenia, the family may want to know more about heritability, and the risk of heritability can be calculated (Gottesman, 1991).

This is a good application as it can provide support and reduce the fears about developing schizophrenia.