Schizophrenia Continued

Twin, Adoption and Family Studies

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Adoption Studies

Main Findings

Families and individuals were assessed. There were 3 main testing areas in the study; genetic boundaries, genotype environment interaction and communication deviance of adoptive parents.

Genetic boundaries; there was not a significant link between mothers with and without schizophrenia for life expectancy. However, adoptees who's mothers that had schizophrenia spectrum disorders were more likely to have schizophrenia related illnesses.

Genotype environment interaction;  there was a significant association in the high-risk group between disordered upbringing and the adoptees spectrum diagnosis. There was no link in the low risk group.

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Adoption Studies

It was found that if the biological mother had schizophrenia, the risk of the adopted child was 5%, however if the mother had a schizophrenia related disorder, the risk rose to 22%. Even when raised away from their biological parents there was a much higher chance of developing the disorder themselves. Something other than living in the home of a person with schizophrenia, must account for this.

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Socially sensitive research, longitudinal study, small sample size (190), application of the findings?

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It was a longitudinal study that was carried out over 21 years and schizophrenia was a predicted disorder within family adoption. However,  only children that carried a genetic link of schizophrenia had a significant association between the measure of adaptive family functioning and the adoptees spectrum diagnosis, but other mental disorders were also found. A subgroup in the study was found to have the same result in terms of the schizophrenia diagnosis spectrum. This shows that adoptees at genetic high risks are more sensitive then adoptees at genetic low risk to both adverse and protective environmental effects in their upbringing.

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This adoption study of the schizophrenia spectrum supports the hypothesis of interaction between genotype and environment.

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Family Studies

Family studies aim to find individuals with schizophrenia and determine whether their biological relatives are similarly affected more often than non-biological relatives.

Family studies discovered that schizophrenia is more common among biological relatives. Mores so the closer the degree of genetic relativeness, thus increasing the risk e.g. mother and son.

Children with schizophrenic parents have a concordance rate of 46%

Children with one schizophrenic parent have 13% chance of the disease. Additionally a sibling of a schizophrenic has 9% chance.

Researchers claim that schizophrenia runs in families due to rearing patterns or other factors and not necessarily due to heredity.

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Gottesman 1991

There are greater risks associated with higher levels of genes.

Third degree relatives (cousins) share about 12.5% of their genes and show a risk of 2% for developing schizophrenia.

Second degree relatives (half-siblings) share 25% and have a risk of 6%

First degree relatives (siblings, dizygotic DZ twins) share 50% of their genes and show 9% risk.

Monozygotic (MZ) twins share 100% and show risk of 50% of developing schizophrenia.

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When looking into explanations of schizophrenia, family studies utilise the biological approach as it explaining schizophrenia in terms of are genetics, saying that the causes are within and are heredity. A strength of this is that precise and accurate prediction can be made as controlled experiments can be carried out enabling the theory to be falsifiable as it provides evidence to support it, this strengths its scientific credibility.

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Evaluation Continued

However the theory is reductionist as its reducing the complex issue of schizophrenia into a simple explanation. It’s over focused on nature ignoring the role of nurture. There was only a 43% concordance rate for those children who had two schizophrenic parents, so it’s not explaining why the other 57% didn’t get the illness, this shows how nurture needs to be taken into consideration, because if it was all down to nature it would be 100% as they have combination of both their parents genes. This shows how schizophrenia is a complex interaction between nature and nurture and alone this theory cannot be valid as its too simplistic and ignores other factors.

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Evaluation Continued

The theory is also deterministic in that it ignores free will. It implies that if both your parents have schizophrenia then you have no choice but to have a high chance of developing it yourself because it’s down to genetics which you have no control over so there’s no room for free will. This is rarely the case, all though there is no cue there are treatments to prevent developing it, so perhaps it’s better to see are genetics as predisposing us to schizophrenia rather than determining whether we get it or not .

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Twin Studies

Twin studies offer a way of establishing genetic links by comparing concordance rates in MZ (monozygotic/ identical) and DZ (dizygotic/fraternal/non-identical).

Concordance rates look at the likelihood that both twins are affected with a disorder.

For example; in a sample there are 100 pairs of twins, one twin of each pair has schizophrenia. The number of times their other twin shows the illness determines the concordance rate. So if 40 of the other twins show the illness, the concordance rate is 40% (40/100)

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Twin Studies Continued

Twins are used because MZ twins share 100% of their genes  and DZ twins share 50% of their genes. Genetic factors can be seen to play a part if MZ twins (with 100% shared genes) are more concordant/similar in terms of disorders like schizophrenia, than the DZ twins (who only share 50%).

Twins are also used because they usually share the same environment, but with some schizophrenic research psychologists seek out twins reared apart, where at least one twin has been diagnosed with the condition. The presence of a separation lets researchers focus more on genetics, rather than the possible behavioural and psychological effects that a schizophrenic twin may have on a unaffected sibling.

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Research into Twin Studies

Joseph 2004: calculated that the pooled data from from all twin studies carried out prior to 2001 showed a concordance rate of 40.4% for MZ twins and 7.4 % for DZ twins. More recent methodological studies (those using blind diagnoses, where the researcher doesn’t know of they are with a MZ or DZ twin) have reported a lower concordance rate.

Despite this researchers still say the genetic factors argument is supported because the concordance rate in MZ twins is still many times higher than the DZ twins concordance rate.

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Twin Studies

Gottesman and shields (1982): used the Maudsley twin register and found 58% (7 out of 12 twins reared apart) were concordant for schizophrenia. According to ‘genetic hypotheses’ (hypotheses based on research into genetics and inheritable traits) this means that children of such twins would also be at risk of developing schizophrenia.

Fischer (1971): found that 9.4% of such offspring developed schizophrenia which is a higher incidence rate that the general population (1%)

A study in London using the Maudsley twin register by Cardno et al (1999) found a 40% concordance rate in MZ twins, compared with 5.3% in DZ twins.

The prevalence of schizophrenia in MZ twins who share more genes, compared to DZ twins who share less, shows support for the genetic explanation of schizophrenia.

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Eurocentric: The Maudsley twin register was a register from Maudsley hospital, Denmark hill London. As such the only infants used would have been born in Britain and most likely would have been from British parents, and bought up somewhere in Britain. We cannot extrapolate the results to other cultures, even if incidence rates of schizophrenia are similar across the world. Every culture is distinctly different, for example differences between individualist and collectivist cultures.

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Though psychologists use twins reared apart to eliminate environmental influences some say that the 9 months in the womb together can have an effect, as the twin are sharing the same environment. As such environmental effects cannot be completely discounted.

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Joseph (2004) looked at concordance rates in twins reared together. An assumption with this type of research is that the environments of MZ and DZ twins are equivalent, therefore the greater concordance of schizophrenia in MZ twins is a product of greater genetic similarity. Joseph (04) points out that MZ twins are more likely to be treated similarly, experience similar things, and experience more ‘identity confusion’. As a result Joseph argues that there is reason to believe that the differences of concordance rates between MZ and DZ twins reflects nothing more than environmental differences instead of genetic factors.

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