Studies show that eating disorders tend to run in families. This suggests genes contribute to eating disorders. Genes cause traits. Several studies show people with eating disorders share traits that existed before the disorder, and they appear to contribute toward maintaining the disorder. For example perfectionism, obsessionality, high achievement orientation, and anxiety are common AN traits. Brain imaging studies show differences in the parts of the brain involved in eating in individuals with eating disorders compared with those who do not have eating disorders. Together, research shows there are strong genetic and neurobiological causes of eating disorders.