Bipolar disorders genetic factors

The precise etiology of bipolar disorder is unknown. Thought to be genetically based, bipolar disorder is influenced by a variety of factors that may enhance gene expression. These include trauma, environmental factors, anatomic abnormalities, exposure to chemicals or drugs, and others.3-5 Neurochemical abnormalities in bipolar disorder may be caused by these factors, as discussed further in the pathophysiology section. 

These data show that for three psychotic disorders (schizophrenia, bipolar disorder and unipolar depression) the genetic contribution is over 50% but for reactive depression (in response to a traumatic life event ) and tuberculosis, an infectious disease caused by a species of Mycobacterium, environmental factors account for over 90% of the variance. 

Both genetic and nongenetic factors play roles in the transmission of mood disorders. The familial nature of mood disorders is well established. Studies over the past 20 years have consistently documented higher rates of mood disorder in the relatives of individuals with major depression and bipolar disorder than in relatives of healthy controls [6,7], The familial aggregation of mood disorders is the outcome of both genetic and environmental factors. 

Although biological and genetic factors are undoubtedly important, they may not explain all the variance in the course and prognosis of a bipolar disorder. 

Bipolar disorder is likely caused by genetic factors, environmental triggers, and the dysregulation of neurotransmitters, neurohormones, and secondary messenger systems in the brain. 

Furlong RA, Ho L, Rubinsztein JS, Walsh C, Paykel ES, Rubinsztein DC (1998) No association of the tryptophan hydroxylase gene with bipolar affective disorder, unipolar affective disorder, or suicidal behaviour in major affective disorder. Am J Med Genet 81 245-247 Gaiter D, Unsicker K (2000a) Brain-derived neurotrophic factor and trkB are essential for cAMP-mediated induction of the serotonergic neuronal phenotype. J Neurosci Res 61 295-301... 

Schumacher J, Jamra RA, Freudenberg J, Becker T, Ohlraun S, et al. 2004. Examination of G72 and D-amino-acid oxidase as genetic risk factors for schizophrenia and bipolar affective disorder. Mol Psychiatry 9 203-207. 

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