genetic explanation for schizophrenia Flashcards
heritable condition, family - P1, A01
the genetic explanation of schizophrenia suggests that schizophrenia is heritable and therefore passed down through families
the fact that there is approximately 0.3-0.7% prevelance worldwide with very little variation by culture, suggests that there must be underlying biological factors to the cause of schizophrenia
a recent estimate for the heritability of schizophrenia is 795 which also suggests a large role for genetic factorss in determining schizophrenia
heritable condition, genes - P1, A01
one approach to understanding the genetic underpinning of schizophreniais to identify responsible genes that are present in family members who have been diagnosed with the disorder
the search for such genes has identified a very large number of possibilites
Wright (2014) indicated that as many as 700 genes have been linked to schizophrenia and this figure is now likely to be in the thousands
heritable condition, twins - P1, A01
as schizophrenia is known to run in families, evidence focuses on twin, family and adoption studies
these studies look at concordance rates, the degree to whcih schizophrenia is shared betwee family members, relative to the amount of genetic material they also share
if a grandparent has schizophrenia, this increases the concordance rate to 5% and of a parent has schizophrenia, this increases the concordance rate to about 13%
strength of heritable conditon - P1, A03
one strength of explaining schizophrenia with a genetic explanation is that there is study evidence to suggest that the condition is heritable
gottesman and shields studied concordance rates in twins
they found that MZ twins who share 100% of their DNA showed 46% concordance rate compared to 17% in DZ twins who only share 50% of their DNA
this study evidence in theory rules out the influence of environmental factors becuase both sets of twins as they are presumed to share environments
therefore, this means that even though schizophrenia is not an entirely genetic disorder the concordance rate is greater for MZ twins than DZ twins which shows that biological factors play a significant part in explaning onset of schizophrenia
COUNTER ARGUMENT TO strength of heritable conditon - P1, A03
however, caution should be excersised when interpreting results from MZ / DZ twin studies; MZs do not only share more DNA than DZs, they are also likely to be treated more similarly due to more similar appearance and the fact that they are always the same sex (DZs can be different sexes)
in addition the similarity between genetic relatives may be as much due to shared environments as it is shared genes
therefore, this reduces the validity of the conclusion that the greater amount of shared DNA is responsible for their similar pathology
gene mutations - P2, A01
schizophrenia is able to appear in the absences of a family history of the disorders
the DNA code in one or more genes may spontaneously change (mutate)
these changes may result from an environmental factor or an error during cell division, such as deletion ot duplication of a strand of DNA
for example. DiGeorge symdrome is caused by the deletion of around 30-40 neighbouri genes located in a specific region of chromosome 23
about 25% of people with this condition go onto experience
strength of gene mutations, application to genetic counselling - P2, A03
one strength of the genetic approach to schizphrenia is that it has been used to inform genetic counselling
when a family member recieves a diagnosis of schizophrenia, the family may want more information about whether the condition is heritable
‘recurrence risk’ can be caluclated and the counsellor will then help the family to interpret this information
therefore, this service can provide support during difficult times, help to allay fears of the inevitability of schizophrenia, while also helping people to make rational choices about family planning
candicate genes - P3, A01
there have been specific genes which have been identified that are linked to the presence of schizophrenia
The COMT gene - the link between schizophrenia and DiGeorge symdrom may be due to the deletion of the COMT gene. this gene provides instructions for the creation of Catechol-O-methyltransferase, an enzyme which breaks down neurotransmitters such as dopamine in the prefrontal cortex. deletion of the COMT gene would mean that dopamine levels are poorly regulated resulting in schizophrenia symptoms
The DISC1 gene - people with an abnormality to the gene Disrupted-in-Schizophrenia 1 (DISC1) are 1.4 times more likely to develop schixophrenia than people without this abnormality. this gene codes for the creation of GABA, a neurotransmitter which regulates other neurotransmitters such as glutamte and dopamine in the limbic system
strength of candicate genes - P3, A01
one strength of candicate genes as an explanation for schizophrenia is the wealth of research evidence
in a review of 14 studies, Tarik Dahounnet al (2017) concluded that DISC1 is associated with presynaptic dopamine dysregulation, a key factor in schizophrenia
Michael Egan et al (2001) proposed a link between decreased dopamine activity in the prefrontal cortex and one form of the COMT gene - the ‘Val’ allele
they conclude that inheriting two copies of the Val allele (one from each parent) increases the risk of schizophrenia by 50%
therefore, this shows how genetic varitions underpin neurochemical difference which canpredispose a person towards schizophrenia
COUNTER ARGUMENT TO strength of candicate genes - P3, A01
however, it can be considered reductionist to suggest that a single gene is responsible for causing such a complex disorder of schizophrenia
there is evidence to suggest that schizphrenia is polygenic with over 700 different genetic variations that could contribute and cause schizophrenia to date
therefore, this means that explaining the cause of schizophrenia with just one gene is reductionst as there are other genetic variations which contribute to the cause of schizophrenia found to date
diathesis stress model - P4, A01
it is suggested that it is most likely that genes create a vulnerability for schizophrenia rather than causing it
an individual may possess ‘schizophrenia’ genes (a diathesis) but the condition is only triggered by other biological or environmental effects
in the diathesis stress model, it is a biological explanation becuase genes are a required elemen in the condition of schizophrenia
the diathesis stress model states that schizophrenia arises from a combinatio of biological vilnerability and environmental triggers
strength of diathesis stress model - P4, A01
one strength of the diathesis stress model is that there is study evidence which suports the view that schizophrenia is caused by a combination of biological and environmental factors
Brown and Birley found that 50% of schizophrenia patietns reported a major life event taking place in the three weeks prior to their relapse
therefore, this means that the study evidence shows that half of the patients used in the study showed that they had a big life event (stress) in the three weeks prior to their relapse which highlights the importance of environmental factors in causing schizophrenia
logical chain of reasoning for strength of diathesis stress model - P4, A01
furthermore, the interactionist approach to schizphrenia (schizophrenia is caused by a combination of biological and environmental factors) can be supported by the debate of the interaction between nature and nurture
Pekka Tierani (1994) carried out a 21-year longitudinal adoption study which supports the diathesis-stress model
adopted children whose biological mothers were diagnosed with schizophrenia were more sensitive to family dysfunction in the adoptice home than those from low-risk matched background
therefore, this supports the view that schizophrenia is caused by a combination of biological and environmental factors when explaining schizophrenia
weakness of genetic explanation for schizophrenia - P5, A03
one weakness of the argument that schizophrenia is genetic is the fact that the concordance rate is far from 100% even for MZ twins
Carsten Pedersen and Preben Mortensen’s (2006) research neatly demonstrates that the longer a person has been exposed to city life and the denser the population in that city, the greater their risk of developing schizophrenia
this suggests that rural dwelling may help protect a person from developing a diorder to which they are genetically predisposed
therefore, this shows just one way that environmental risk factors can affect individuals therefore accounting for how it is possible for MZs to differ so much in terms of onset of schizophrenia
