There is a genetic component to the neurobiological stress response.  Family transmission has been shown to be associated with stress disorders.  There is also an important development component.  Social support is well known to be associated with a person’s ability to cope.  Animal studies have shown that when subjected to uncontrollable stress in infancy, they are more likely to have increased stress reactivity in adulthood (Southwick, 2007).    People who have been subjected to neglect or abuse as children are particularly vulnerable.