Bipolar disorder, formerly manic depression, is a typically chronic mental illness characterised by extreme changes in mood and energy. Depending on the type of bipolar and severity, an individual may experience periods of severe depression that alternate with manic, hypomanic or mixed episodes. Both ends of the bipolar spectrum are often so severe that they interfere with everyday tasks and can, at times, compromise an individual’s ability to function in the community. Ultimately, as with most mental illnesses, bipolar disorder results from a complex combination of both genetic and environmental factors, but causative research, and hence our understanding of the illness, is ever-developing.
There are several classifications of bipolar disorder, hence it can be considered a spectrum of severity: cyclothymia, bipolar II and Bipolar I disorder, in addition to bipolar NOS (not otherwise specified), where cyclothymia is the least severe and bipolar I the most severe. An individual with a milder form of bipolar disorder has an increased risk of progressing to a more severe variant of the disorder. Studies suggest that individuals with bipolar I disorder first experience less severe symptoms on average 12 years prior to being diagnosed (1). The median age for onset for bipolar disorder ranges from 17 to 31, with the first peak occurring between 15 and 19 years of age.
A person is thought to be born with a “vulnerability” to bipolar disorder, meaning that they are more prone to developing the disorder (2). In fact, there are specific abnormalities in emotional processing and regulation of neural circuitries in offspring at risk for bipolar disorder, i.e. offspring of a patient with bipolar disorder. A neuroimaging study showed there to be greater activity and functional connectivity during emotion regulation tasks (facial processing) in the anterior cingulate cortex that may help to distinguish youth at risk for bipolar disorder from healthy youth (3).
The genetic component to bipolar disorder is still largely mis-understood. A study by UCLA used a new, innovative approach, far from the traditional clinical interview of symptoms in the diagnosis of bipolar disorder: Researchers combined the results from brain imaging, cognitive testing, and an array of temperament and behaviour measures (3). Whilst the specific genes that contribute towards the illness are still unidentified, about 50 brain and behavioural measures under strong genetic control were found to be associated with bipolar disorder. Interestingly, it was found that the thickness of the grey matter in the brain’s temporal and prefrontal regions were both genetically linked and associated with the disease. These structures are critical for language, self-control and problem-solving. This identifies a potential target trait for genetic mapping and identification of disrupted biological pathways vital for the disease.
To summarise, bipolar disorder has several variants of severity. Development of the more severe bipolar I disorder increases in likelihood should an individual present with the less severe symptoms of cyclothymia. The average age of emergence for bipolar disorder is 19, although many patients first experience symptoms prior to seeking treatment and obtaining a correct diagnosis. The cause of bipolar disorder is ultimately unknown; a combination of environmental ‘triggers’ and genetic factors are necessary for the development of the disorder. An individual may possess a genetic “vulnerability” to bipolar disorder, and present with abnormalities in emotional processing and regulation in neural circuitries. A previous study showed there to be 50 brain and behavioural measures, that are under strong genetic control, associated with bipolar disorder. Of particular interest, the thickness of the grey matter in the brain’s temporal and prefrontal regions were linked to the diease, and mark a potential target for genetic mapping.
- History of illness prior to a diagnosis of bipolar disorder or schizoaffective disorder. Berk M, Dodd S, Callaly P, Berk L, Fitzgerald P, de Castella AR, Filia S, Filia K, Tahtalian S, Biffin F, Kelin K, Smith M, Montgomery W, Kulkarni.J Affect Disord. 2007 Nov; 103(1-3):181-6.
- https://www.heretohelp.bc.ca/factsheet/bipolar-disorder-what-causes-bipolar-disorder
- https://jamanetwork.com/journals/jamapsychiatry/article-abstract/2697854?resultClick=1
- http://newsroom.ucla.edu/releases/coming-soon-249997
The Science of Mental Illness 