Studies have found that children are at higher risk of depression if one parent has a history of depression, and that risk is even higher if major depression affects both parents.

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Depression manifests itself in many different ways. A person may become withdrawn, scatterbrained or extremely irritable. Sleep may go into overdrive or become scarce. Appetite may also be at one extreme or the other. Feelings of hopelessness, sadness or anxiety may dominate for weeks, months or even years.

Major depression (the clinical term for depression) is found among all demographics, affecting both men and women of all ages, even children. It may seem to settle in out of the blue or it can be triggered by an upsetting life event. In a given year, about 7 percent of American adults experience major depression [source: Simon].

Many different things can trigger a depressive episode. Loss of a loved one and divorce are high on the list for depression triggers. So too are health problems and job loss. Abuse of alcohol and drugs can also create a cycle of depression, wherein one attempts to alleviate feelings of depression with the very same substance abuse that partly spurred the condition in the first place. However, less obvious events -- like poor academic performance or traumatic events from the distant past -- can also play a hand.

For the person experiencing major depression, life can become hellish. Friendships may be abandoned, jobs may be lost and healthy lifestyle habits shunned. Previous joys -- hobbies, interests and activities -- become joyless. Suicide may not only begin to seem like a plausible option, but even perhaps the only available option.

Living with a person experiencing major depression is no bowl of cherries either. Depression can be difficult for family members as they grapple to understand behaviors of a loved one who has given up hope.

But blood relatives may have another hurdle to cross in their dealings with a loved one's depression: their own increased risk of one day battling major depression themselves. Does major depression run in families? What do the experts say? And what other factors may increase risk? We'll discuss these questions in the next section.