The genetics of depression and suicide are not fully understood

Dear Doctor: Does depression run in families? That is, is it inherited? Enough to make a person suicidal?

Dear Reader: The short answer is, yes, depression can run in families. But first some background: Depression is quite common in the United States. About 17 percent of the population will have an episode of major depression at some point -- one that lasts at least two weeks and is marked by a depressed mood most of the day, decreased pleasure in doing activities, poor concentration, feelings of worthlessness or hopelessness, fatigue and possibly the desire to commit suicide. Another 3 percent will have persistent depression, in which symptoms are fewer but last longer.

Genetics do appear to play a role. Studies of identical twins have found that if one twin has a depressive episode, the other twin has a 37 to 38 percent chance of depression. These twin studies show a stronger correlation in women than in men (42 percent versus 29 percent), and a Swedish study found a greater chance of major depression if the other twin had depression early in life (from ages 13 to 23).

The genetics of depression are not simple. No one gene has been implicated. Multiple genes could be involved, and they could vary based upon race. Further, some trigger in the environment (a stressful life event or isolation) could cause a gene to be turned on, leading to depressive symptoms.

Suicide appears to be a separate issue. Suicide clearly has, in part, a genetic connection. The genes involved, however, may be more related to impulse control than depression. One study found that among identical twins, if one twin commits suicide, the other twin has a 14.9 percent risk of suicide. This was much higher than the 0.7 percent rate seen in non-identical twins. Another study found an even stronger connection -- that if one identical twin commits suicide, the other twin attempts suicide 38 percent of the time.

The risk of suicide goes beyond twins. A 2003 Swedish study found that suicide rates are twice as high in families of suicide victims compared to those families without a suicide victim. This data was independent of depression. Other studies have shown that rates of suicide among adolescents are much higher if a first-degree relative has committed suicide.

The issue appears to be one of an aggressive impulse, which can lead to a suicide attempt. Although a depressed person might think about suicide, a person who has a close family history of suicide might have a greater impulse to actually attempt it. The combination of both depression and a family history of suicide will thus increase the likelihood of a suicide attempt.

As we've established, the genetics of depression and suicide are not fully understood. Additional risk factors might include exposure to abuse, an unstable home environment and economic instability. So, although a family history of suicide and depression can increase the risk of these same ailments, a nurturing home life, economic security and personal well-being will mitigate this risk.

If you're showing signs of depression or having thoughts of suicide, please seek professional help as soon as possible.

Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.