Phenotype, endophenotype, and genotype comparisons between borderline personality disorder and major depressive disorder.

Borderline personality disorders (BPD) and major depressive disorder (MDD) are distinct disorders with overlapping biological processes pertaining to emotional regulatory functions. However, while both disorders share affective symptomatology, the disturbance central to BPD is affective lability and its character is entirely different from the affective disturbance of MDD. This review highlights data from the last ten years and compares the two disorders' phenotypes, putative endophenotypes and genotypes, focusing heavily on neuroimaging findings. The familiality and phenotypic differences suggest that BPD differs in important ways with respect to symptomatology, prognosis, and heritability. The neurobiological findings in both MDD and BPD are still preliminary at present, and no coherent model for either disorder can be said to have emerged. Overlapping biological processes including amygdala hyperreactivity, volume changes in subgenual anterior cingulate cortex, and deficient serotonergic function appear to underlie emotional dysregulation in both disorders. However, the disorders seem to differ in their patterns of brain region involvement, neurohormonal indices, and sleep architecture. At present, the minimal data available for putative genotypes of BPD is still emerging, nonspecific to the disorder and demonstrates significant overlap with MDD. The ability to discern commonalities and differences in the neurobiology of these two disorders is limited by the differing methodologies applied in different studies. Definitive clarification of what MDD and BPD have in common and in what ways they are distinct will only be derived from studies that examine both illnesses using the same study design and methodology.