Another major finding has been the repeated empirical documentation of important genetic overlap (particularly common variation) between most or all adult- and childhood-onset psychiatric disorders (26, 27). It is clear that psychiatric nosology has not “carved nature at the joints”. Moreover, the common variant genetic architecture of many disorders blends into normal phenomena. For example, there are sizable genetic correlations of MDD with personality traits like neuroticism and readily-assessed depressive symptom measures. Other findings suggest reconceptualizations may be needed. For example, anorexia nervosa had a significant positive genetic correlation with schizophrenia, significant negative genetic correlations with body mass index and unfavorable metabolic measures, and significant positive genetic correlations with favorable metabolic factors. This pattern of findings suggests that the roots of anorexia nervosa may be not only psychiatric, but also metabolic in origin.
