It is thought Schizophrenia runs in families and the closer the relative, the higher the pobability of it being passed down to you. To try and prove this link, Three types of study are used.
- Family Studies: Gottesman (1991) found that first degree relatives share 50% of their genes and the closer the genetic relationship the higher risk of schizophrenia developing. Kendler et al found that those who are first degree relatives to someone with schizophrenia are 18 times more likely to develop the disorder.
- Twin Studies: They try to find MZ (Identical) twins who have been raised apart where one has developed schizophrenia. Raised apart so that environmental factors can be excluded.
- Adoption Studies: Try to find children raised apart from their biological parents where one has developed schizophrenia, Tienari et al (2000) found those with a schizophrenic mother had a higher chance of developing the disorder than the general population.
Family Studies: Conducted retrospectively meaning the results would not be as accurate which leaves the stud open to errors in the results. A way to fix this would be to do a prospective longitudinal study and then compare conditions before and after.
Twin Studies: Even though the twins have been raised apart there is still the 9 months they initially shared in the womb so environmental factors cannot be entirely disregarded. An added problem would be the complication of the reason behind why they were seperated in the first place.
Adoption Studies: The research provides a strong link gentetic link in schizophrenia. Wahlenburg et al (2000) re-examined the data from Tienari et al (2000) finding that only when there was poor communication within the adoption family was there an increased chance of schizophrenia.
All round the genetic link shows a higher risk or schizophrenia but not 100% definite.
It has been found that schizophrenics have an abnormally high level of Dopamine D2 Receptors which then makes them more suceptable to Dopamine. Dopamine neurons play a role in the attention system so a disruption with this system could result in issues with attention and perception.
The role of Dopamine is reinforced through two sources of evidence:
1. Amphetamines: Amphetamines stimulate nerve cells in the brain that contain dopamine which floods the synapses with the neurotransmitter and produces schizophrenic like symptoms such as hallucinations and delusions. These are Agonists.
2. Anti-psychotic Drugs: Anti-psychotic drugs have been shown to block the activity of dopamine in the brain and reducing the stimulation of it, this helps to alleviate some of the symptoms. This is an Antagonist as it blocks the action.
Dopamine Hypothesis Evaluation
Its hard to establish the cause and effect, does higher levels of dopamine cause schizophrenia or does schizophrenia cause higher levels of dopamine??
In the past post-mortem brain dissections were done however with today's technology using PET scans the levels of dopamine can be shown in a living person, these scans support the link as higher dopamine levels have been found.
Drug Therapies have been found to be successful in treating the Type 1 symptioms (Positive) but not Type 2 symptoms (Negative) therefore making the Dopamine Hypothesis Reductionist as it shows there is other factors involved.
The drug Clozapine has been found to help schizophrenics by effecting the levels of seretonin, this shows that it is not all down to dopamine.