234 Eating Disorders
of eating disorders is the most productive (Szmukler, Dare, and Treasure,
1995), although what such a model would look like remains unclear.
A physiological model of eating disordersSome researchers have explored the physiological basis for eating disorders.
This has involved an examination of genetics in terms of family clusters
and the use of twin studies and an emphasis on neurotransmitters.
A genetic model
Eating disorders appear to run in families. Strober et al. (1990) reported
that female relatives of patients with anorexia nervosa were 10 times more
likely to develop an eating disorder than the control population. Strober
et al. (1985) also reported that the risk of anorexia was increased among
second-degree relatives of sufferers. Bulimia is also more common in families
of patients with bulimia nervosa (Strober et al., 1990). Interestingly, the
type of eating disorder appears to be specific, with anorexia being more
common in families of anorexics and bulimia being more common in
families of bulimics. Clustering within families suggests a role for genetics
but cannot rule out the impact of a shared environment. Therefore,
researchers have carried out twin studies using both monozygotic and
dizygotic twins.
Twin studies are often presented as the “best case” method for deter-
mining the genetic basis to a given problem, as they purport to enable the
separation of genetic and environmental factors. There are some problems
which need to be considered. For example, zygosity needs to be determined
accurately, the selection of twins is often difficult, particularly if the condi-
tion being studied is rare, and the sample selected must be deemed to be
representative of twins in general rather than those twins with the condition
under question. In addition, there remains the problem of the environment.
It is assumed that the environment of identical twins is as similar as the
environment for nonidentical twins. However, it is possible that identical
twins are treated in a more similar way than nonidentical twins. Further,
if adoptee studies are used, it is possible that the environment of the
adoptive family is still very similar to that of the biological family.
Given these methodological issues, research has addressed the role of
genetics in the etiology of eating disorders. In terms of anorexia nervosa,
research based in London using patients from two specialist eating disorders
centers reported that 55 percent of identical twins were concordant for