Biology of bipolar disorder

Bipolar disorder is an affective disorder characterized by periods of elevated and depressed mood. The cause and mechanism of bipolar disorder is not yet known, and the study of its biological origins is ongoing. Although no single gene causes the disorder, a number of genes are linked to increase risk of the disorder, and various gene environment interactions may play a role in predisposing individuals to developing bipolar disorder. Neuroimaging and postmortem studies have found abnormalities in a variety of brain regions, and most commonly implicated regions include the ventral prefrontal cortex and amygdala. Dysfunction in emotional circuits located in these regions have been hypothesized as a mechanism for bipolar disorder.^[1] A number of lines of evidence suggests abnormalities in neurotransmission, intracellular signalling, and cellular functioning as possibly playing a role in bipolar disorder.^[2]

Studies of bipolar disorder, particularly neuroimaging studies, are vulnerable to the confounding effects such as medication, comorbidity, and small sample size, leading to underpowered independent studies, and significant heterogeneity.^[4]