ABSTRACT
For most psychiatric disorders, little is known about the nature of the underlying pathophysiologic and psychologic mechanisms. This makes it difficult to determine if two mental disorders that frequently co-occur are truly different disorders or different expressions of the same disorder. For example, is major depression (MDD) diagnosed in an individual with borderline personality disorder (BPD) the same disease as MDD diagnosed in an individual without BPD? If not, could co-occurring MDD and BPD be different manifestations of the same underlying disease process?
