The family tree may hold clues about the roots of chronic depression.

A study in The American Journal of Psychiatry shows that chronic depression may be apt to strike more than once in an immediate family.

The study looked at 638 people who developed major depression before age 31 and 1,085 of their relatives -- parents and siblings who had also had an episode of major depression.

The researchers found that the parents and siblings were two and one-half times more likely to have chronic depression if their family member had also had chronic depression, rather than recurrent depression.

They also found that the relatives studied were six times more likely to have chronic depression if their family member had become chronically depressed by age 13.

Chronic depression, which accounts for a “large minority” of those with depression, was defined as being depressed “most or all of the time since the illness [depression] first started,” says researcher James Potash, MD, MPH. Potash is associate professor of psychiatry and co-director of the mood and disorders program in Johns Hopkins University’s psychiatry department.

The Genetic Connection

Remember, relatives who had never been depressed weren’t included in the study. So the odds cited don’t apply to the entire family.

“If somebody said, ‘Well, I’ve got three brothers. And one of them has depression, and two of them are the healthiest people you’ve ever seen,’ we didn’t try to interview the healthiest people you’ve ever seen,” Potash says.

“So we don’t actually know for sure how many unaffected relatives there actually are,” he says.

Genetics and environment are probably both involved in depression, and it’s not clear how they interact.

“We know there is a genetic aspect to it,” Potash says.

“We’re not at the point yet where we’ve been able to nail down which genes are involved, but that’s what we’re working hard at in this next phase of the study.”

More Research Needed

Potash encourages people to consider taking part in depression research.

“Certainly, one of things that people can do to make a difference is to participate in research,” he says. “Because this study and others like it are the things that are ultimately going to lead to better treatments.”

Depression is “the fourth most disabling illness in the world, but we understand remarkably little about what causes it or how it unfolds in the brain,” he says. Potash says the disease is “one of the most important public health issues.”

Not Just About Feeling Sad

Potash points out that depression can show itself in several ways.

“Everybody knows about feeling sad and crying,” he says.

“People may be a little less aware of the fact that one of the cardinal symptoms of depression can be, rather than sadness, a sense of emptiness or numbness, a kind of lack of feeling anything,” Potash says.

“Another thing we see often in these patients is a chronic sense of being inadequate, chronically low level of confidence or self-esteem,” he notes.

“Other important symptoms include disrupted sleep [and] low energy,” Potash says.

Depression can often be treated, so it’s important to seek help.

By Miranda Hitti, reviewed by Louise Chang, MD

SOURCES: Mondimore, F. The American Journal of Psychiatry, September 2006; vol 163: pp 1-7. James Potash, MD, MPH, associate professor of psychiatry, Johns Hopkins University School of Medicine; co-director, Johns Hopkins Mood Disorders Center.