It may be helpful to think of the various mood states in manic-depressive illness as a spectrum or continuous range. In the other extreme, mania may be the main problem and depression may occur only infrequently. The risk of manic-depressive illness is the same for both sexes. The onset of the illness can occur at any age, but bipolar disorders typically begins in adolescence or early adulthood and continues throughout life. It is often not recognized as an illness, and people who have it may suffer needlessly for years or even decades.
Bipolar disorder tends to run in families and is believed to be inherited in many cases.
Despite vigorous research efforts, a specific genetic defect associated with the disease has not yet been detected. In its early stages, bipolar disorder may masquerade as a problem other than mental illness. For example, it may first appear as alcohol or drug abuse, or poor school or work performance. Hypomania may feel good to the person who experiences it. Unfortunately, even when family and friends learn to recognize the mood swings, the individual often will deny that anything is wrong.