The exact etiology, or cause, of Antisocial Personality Disorder is unknown. It has been hypothesized that it is caused by abuse or emotional deprivation as a child, but it appears to be caused by environmental as well as genetic factors. It has also been hypothesized that the amygdala in the brain, which controls one's responses to stress, is malfunctioning in people with ASPD and this could explain their lack of emotion or response to emotionally stressful situations. A genetic link in ASPD is also supported by the increased likelihood of an individual developing the disorder if a first-degree relative has it.
Please note that these are all hypotheses as to the cause of ASPD and none are the proven cause of the disorder.