Many clinicians have held the view that borderline personality disorder (BPD) is solely or mainly the product of environmental risks, ranging from aversive childhood experiences to organic trauma, but Kernberg 8 proposed that the basic core in the development of BPD organization may be an inherited, unusually strong, aggressive drive associated with an inborn deficiency in the ability to tolerate anxiety. Linehan and Koerner 11 suggested that the basis for BPD is an inherited biological predisposition to emotional dysregulation. This dysregulation implies an accentuated sensitivity to emotional stimuli; intense reactions to such stimuli; and a slow, delayed return to a normal emotional level. Dysregulation means a lack of the ability to control impulsive behavior related to strong positive and negative effects, a lack of ability to comfort oneself when strong effects give intense physiologic outcomes, problems in turning attention toward other aspects, and difficulties in organizing and coordinating activities to achieve one's goals. These investigators did not imply that biology is the only determinant. Linehan and Kramer 11 suggested that an invalidating childhood environment is also necessary for the development of BPD. To determine whether BPD is influenced by genetic factors, a series of systematic empiric studies must be reviewed.