Classification and neurobiological concepts of mania, bipolar disorder and major depression

Excerpt

In the new DSM-5 and ICD-11 classification systems, pure mania and mania with mild depression are subsumed under bipolar disorder. In a comprehensive review, Angst and Grobler [1] vote for improved differential diagnoses of unipolar mania. This is clinically relevant since the disorder has a prevalence of approximately 1.8 %, and clinical follow-up studies demonstrated good diagnostic stability. Moreover, mania is associated with a hyperthymic temperament, more psychotic symptoms and higher heritability compared with depression. In contrast, the concept of bipolar disorder has been widely investigated in neurogenetic studies. For example, the dopaminergic system has been suggested to be affected in bipolar disorder, but the impact of the genetic variants of the human dopamine transporter DAT1 (SLC6A3) is inconsistent. Huang et al. [2] investigated the association of 18 polymorphisms of the DAT1 gene with bipolar disorder and explored its influence on specific personality traits such as novelty seeking and harm avoidance. Several polymorphisms had a weak association with bipolar disorder, and the promotor G-A-C-G haplotype was overrepresented in their sample of 492 patients compared with 436 healthy controls. Bipolar II patients had the highest harm avoidance score and a significant association between rs40184 of DAT1 and this personality trait in patients with bipolar disorder. G72 (D-amino acid oxidase activator, DAOA) is a susceptibility gene for bipolar disorder and schizophrenia. In a diffusion tensor imaging (DTI) study, Nickl-Jockschat et al. [3] investigated the influence of a G72 susceptibility haplotype on fiber tract integrity in young healthy probands. They found clusters of increased fractional anisotropy in homozygous risk haplotype carriers in the right periinsular and inferior parietal region. Both regions have been hypothesized to be involved in the pathophysiology of bipolar disorder and schizophrenia, and alterations in fractional anisotropy may reflect changes in neuropil such as morphology of dendrites. …