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How many genetic explanations of SZ are there?



What are the 3 genetic explanations of SZ?

1) Family studies
2) Twin studies
3) Adoption studies


What are family studies for SZ?

They find individuals who have SZ and determine whether their biological relatives are similarly affected more often than non-biological relatives


What have family studies found for SZ?

Established SZ more common among biological relatives of person with SZ, and the closer the degree of genetic relatedness, the greater the risk - children with SZ parents have a concordance rate of 46%, children with 1 have 13% and siblings is 9%


Outline twin studies for SZ

If MZ twins who share 100% of their genes are more concordant in terms of SZ than DZ twins who only share 50% of genes, suggests greatest similarity is due to genetic factors


Name the 2 studies for twin studies for SZ

1) Gottesman (91)
2) Joseph (04)


Outline Gottesman (91)

Suggests SZ inherited through genes - studied 40 pairs of twins and found concordance rate for MZ twins was 48% and only 17% for DZ twins


Outline Joseph (04) for twin studies

Calculated that pooled data for all SZ twin studies carried out prior to 2001 shows concordance rate for MZ as 40.4% and for DZ twins as only 7.4%


What have twin studies shown recently for SZ?

More recently, methodologically sound studies (blind diagnoses) tended to report lower concordance rates for MZ twins - despite this, researchers still argue even these findings support the genetic position as provide a MZ concordance rate many times higher than DZ concordance rate


Outline adoption studies for SZ

Due to difficulties of disentangling genetic and environmental influences for individuals who share genes and environment, studies of genetically related individuals who have been reared apart can be used


What is the main study for adoption studies for SZ?

Tienari (00)


Outline Tienari (00)

Of the 164 adoptees whose biological mothers diagnosed, 11 (6.7%) also received diagnosis compared to just 4 (2%) of the 197 control adoptees born to non-SZ mothers - concluded showed genetic liability to SZ had been 'decisively confirmed'


What are the other 2 biological explanations for SZ besides the genetic ones?

1) The dopamine hypothesis
2) Neuroanatomy


What does an agonist mean?

A drugs that binds to and alters the activity of a receptor


What does an antagonist mean?

A drug that binds to a receptor but which does not alter the activity of the receptor


What is dopamine?

A neurotransmitter found in the brain


Outline the dopamine hypothesis

States brains of SZ patients produce more dopamine - states messages from neurons that transmit dopamine fire too easily or too often, leading to characteristic symptoms of SZ - SZs thought to have abnormally high numbers of D2 receptors on receiving neurons, resulting in more dopamine binding and therefore more neurons firing


Name a big study relating to the dopamine hypothesis

Comer (03)


Outline Comer (03)

Dopamine neurons play a role in guiding attention so disturbances in process may lead to the problems relating to attention, perception and thought found in people with SZ


What are the 4 sources of evidence which support the role of dopamine in SZ?

1) Amphetamines
2) Antipsychotic drugs
3) Parkinson's disease
4) Post-mortem studies


What are amphetamines relating to dopamine?

Dopamine agonists


Outline how amphetamines support the dopamine hypothesis

It is a drug which stimulates nerve cells containing dopamine, causing the synapse to be flooded with the neurotransmitter - large doses can cause characteristic hallucinations and delusions of SZ episode


What are antipsychotic drugs relating to dopamine?

Dopamine antagonists


Outline how antipsychotic drugs support the dopamine hypothesis

There are many different types but all block the activity of dopamine in the brain - by reducing stimulation of dopamine system, drugs eliminate symptoms like hallucinations and delusions - the fact that these drugs alleviated many symptoms of SZ strengthened the case for dopamine being a significant contributory factor in this disorder


Outline how Parkinson's disease supports the dopamine hypothesis

Those with the disease have low levels of dopamine and Grilly (02) found some taking drug L-dopa to increase dopamine were developing SZ-like symptoms


Outline Grilly (02)

Found some taking drug L-dopa to increase dopamine were developing SZ-like symptoms


What is the main post-mortem study supporting the dopamine hypothesis?

Falkai (88)


Outline Falkai (88)

Looked at autopsies and found SZs had larger than normal numbers of dopamine receptors - there was an increase of dopamine in brain structures and receptor density so concluded dopamine production was abnormally high in SZs


Outline the role of neuroanatomy in SZ

There is growing evidence that SZ is associated with physical abnormalities in the brain - Szesko found asymmetry that was found in normal brains and that SZs tend to have symmetrical brains - also tend to have abnormally large ventricles in the brain which means brains of SZs are lighter than normal


What are ventricles?

Fluid-filled cavities in the brain