A clear cause for the narcissistic personality disorder has not yet been found. As with many mental conditions, it is believed that NPD is a result of both nature and nurture. Studies have suggested that there is 45-80% heritability, meaning that these traits are passed on from a parent to a child, supporting the genetic cause of the disorder. This means that traits that have to do with sensitivity, aggression and low levels of anxiety can be passed down to a child from a family member. 