Keel, P.K., Klump, K.L., Miller, K.B., McGue, M. & Iacono, W.G. (2005). Shared Transmission of Eating Disorders and Anxiety Disorders. International Journal of Eating Disorders, 38, 99-105.
ABSTRACT
Objective: Eating disorders have high comorbidity with mood, anxiety, and substance use disorders. Using twins from the population-based Minnesota Twin Family Study (MTFS), we examined comorbidity and shared transmission between eating pathology and these disorders.
Method: Female twins (N ¼ 672), ages 16–18 years, completed structured clinical interviews assessing anorexia nervosa and bulimia nervosa (as described in the 4th ed. of the Diagnostic and Statistical Manual of Mental Disorders [DSM-IV; American Psychiatric Association, 1994]), as well as mood, anxiety, and substance use disorders (as described in the 3rd Rev. ed. of the Diagnostic and Statistical Manual of Mental Disorders [DSM-III-R]). Shared transmission was examined using a discordant monozygotic (MZ) twin design.
Results: Significant comorbidity was found between eating disorders and major depression, anxiety disorders, and nicotine dependence. Within MZ twin pairs discordant for eating disorders (n ¼ 14), non–eating-disordered cotwins demonstrated increased risk for anxiety disorders compared with controls. Similarly, within MZ twin pairs discordant for anxiety disorders (n ¼ 52), non–anxiety-disordered cotwins demonstrated increased risk for eating disorders compared with controls.
Discussion: Findings support shared transmission between eating disorders and anxiety disorders. However, the nature of this shared diathesis remains unknown.

Legrand, L. N., M. McGue, et al. (1999). "A twin study of state and trait anxiety in childhood and adolescence." J Child Psychol Psychiatry 40(6): 953-8.
Little research has addressed the relative influence of genetic and environmental factors on subclinical levels of anxiety in children. Of the two twin studies to date, one concluded that measures of adolescents' self-reported trait anxiety were best explained by shared environmental factors (Thapar & McGuffin, 1995), while the second determined that approximately half the variance was attributable to genetic effects (Topolski et al., 1997). The present study, using a sample of 547 twin pairs, reached conclusions similar to those of Topolski et al. Heritability was estimated at 45%. Measures of state anxiety conformed more closely to Thapar and McGuffin's findings, with environmental factors accounting for the variance.