Biological Explanation for Anorexia Nervosa

Biological Explanation for Anorexia Nervosa

Evidence for a faulty gene.

AIMS:

to see if concordance rates for anorexia are higher in MZ twins

compared to DZ twins. This would provide evidence for a faulty gene

causing the disorder because if one MZ twin develops anorexia, there

should be 100% concordance (agreement) with the second MZ twin also

suffering from it, since they share the same genes. The rates for DZ

twins should be much lower because they share only 50% same genes.

PROCEDURE:

· Natural experiment: because the IV (genetic relatedness) occurs

naturally and cannot be changed by the investigator. Longitudonal

study carried out (over time) to see if the second twin developed the

disorder (the DV).

· 34 pairs of twins were studied, and 1 set of triplets, chosen by

opportunity sampling where one member of the twins suffered anorexia;

twins were defined as MZ or DZ after completing a physical resemblance

questionnaire (16 MZ, 14 DZ twins). If there was any doubt, a blood

test was done to establish genetic relatedness.

· Diagnosis of anorexia was based on standard clinical criteria

FINDINGS:

· 9 out of 16 (56%) MZ twins were concordant for anorexia

· 1 out of 14 (7%) DZ twins were concordant for anorexia

· In 3 cases where the second twin did not develop anorexia, they did

develop other psychiatric disorders and two suffered from minor eating

disorders.

CONCLUSIONS:

· The findings show that there is a much higher concordance rate for

anorexia in MZ twins compared to DZ twins

· This suggests provide good evidence for genetic f...

... middle of paper ...

...ctionist, as there is equally

good evidence from other approaches (eg. biological, cognitive,

psychodynamic)

· Natural experiments lack complete control over variables (IV not

manipulated), so the causes cannot be determined ie. cannot be sure

that gender identities and eating disorders are causally related

because the results might be due to uncontrolled variables

· Gender identity was assessed after eating disorders developed, which

cannot test the hypothesis that gender identity causes an eating

disorder to develop. At best, the results simply suggest an

association between gender identity and eating disorders. Ideally

gender identity should be measured first in healthy participants, then

see if those classified as having feminine gender identity go on to

develop eating disorders.

(Holland et al, 1988)