Biological and Genetic Causes of Mood Disorders
Genetic factors have been implicated in Mood Disorders. Both Bipolar and Unipolar have been found to get influenced by biological factors, though genetic risks are particularly strong for Bipolar Disorders. There have been many studies that have reported higher concordance rate for Uni and Bipolar Disorders for monozygotic twins than dizygotic twins, thereby suggesting the role of genetic factors in the causation of Mood Disorders.
Bowman & Nurnmerger (1993) reported in their study that Major Depressive Disorder is about four times more likely to occur in both members of identical twins, compared with non-identical twins. Evidence for a genetic component in mood disorders has also been found in family studies comparing the risk of mood disorders. These studies have consistently shown that close relatives of adults with major depressive disorder are at higher risk for such disorders than are more distant relatives.
Of course, greater environmental similarities in the lives of close relatives might help account for the results of family studies, so researches have also used adoption studies to determine the relative contributions of genetic versus environmental factors. One adoption study found that percent of the biological parents of adoptions with bipolar disorder also had a mood disorder, compared with only 2% of the parents of adoptees with no psychiatric disturbance (Mendelwicz & Rainer 1977).