Biological explanations of anorexia nervosa

An estimated to affect 0.3-1.2% of population. 

85% sufferers female. 

Symptoms include: a refusal to eat, intense dieting, a pathological fear of gaining weight, a distorted body image, self-disgust and food-related anxiety.

Genetic explanations

Families:

• AN is transmitted thorugh hereditary means
• 1st degree relatives of people with AN are approx 10x greater lifetime risk of having AN than relatives of unaffected individuals. 
• Also increased risk of developing other eating disorders, eg. bulimia.
• MZ v DZ twins. Holland et al found 56% MZ and 5% DZ. Replicated in 1995 and found 65% MZ and 32%DZ.

Candidate gene:

• Epoxide hydrolase 2 (Ephx2) - codes for an enzyme involved in cholesterol metabolism and people in the acute phase of AN, with severe symptoms have abnormally high levels of cholesterol.

Strengths:

• Bulik et al - found incidence of AN was 1.2% for female twins and 0.29% male twins, with the heritability of the disorder at 56%.
• Scott-Van Zeeland found a variant of the EQHX2 gene, in a sample of over 3000 females. \

Weakness:

• Diathesis-stress model - genetic vulnerability and environmental trigger, eg. stressor (tryign to lose weight), social cultural or psychological reasons. 

Neural explanations

Serotonin:

• High levels of S cause AN. High levels create a sense…