Depressive disorders genetic factors

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. 

Mania, manic-depression and depression, which comprise the affective disorders, are relatively common it has been estimated that there is an incidence of at least 2% in most societies throughout the world. There is good evidence to suggest that genetic factors play a considerable role in predisposing a patient to an affective disorder. In a seminal Danish twin register study, in which the incidence of affective disorders was determined in all twins of the same sex born in Denmark between 1870 and 1920, a total of 110 pairs of twins were identified in which one or both had manic-depression. The concordance rates, that is the rate of coexistence of the disorder in twin pairs, for all types of affective disorder were found to be... 

I want to reemphasize that drug-induced disturbances in mood or in behavior should be viewed as genuine neurological disorders rather than as vague mental illnesses. The capacity of speculative biochemical imbalances or genetic factors to cause or contribute to mania or depression remains unproven. Nor do we know the specific biochemical or neurological mechanisms whereby psychoactive substances cause mental disturbances. But the capacity for psychoactive substances to disrupt brain function and hence mental function is beyond dispute. Furthermore, a great deal of empirical data confirm their capacity to cause disinhibition, mania, depression, and other mental phenomena associated with violence toward oneself and others, as well as other destructive behaviors. 

Jim TY, Pae CU, Hoon H, Chae JH, Bahk WM, Rim KS, Senetd A (2003) Possible associadoii between -G308A tumour necrosis factor-alpha gene polymoiphism and major depressive disorder in die Korean populadon. Psychiatr Genet 13 179—181. 

In summary, the etiology of major depressive disorder suggests a genetic component, environmental influences, and other, as yet undetermined factors. 

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. 

---