Genetic Influences in Some Depressions

Excerpted from
When a Parent is Depressed: How to Protect Your Children from the Effects of Depression in the Family
By William R. Beardslee, M.D.

When you think of risk factors for depression, it may be genetics that first leaps to mind. The fact remains, however, that there is no strict genetic determinant for the vast majority of depressions.

To date, no single gene has been identified for the transmission of depression. In those instances in which there is a genetic component, several different genes are responsible, operating either in relationship to one another or separately.

Genes are most likely to be involved in families in which there is an extensive, well-described, detailed history of a severe mood disorder, especially mania, in a large number of first-degree relatives - parents, grandparents, aunts, and uncles - across several generations. Genetics is also more likely to be involved in such families when there are long-standing episodes of depression or mania in the absence of any severe environmental adversities such as job loss or exposure to violence. But still, it is the assembly of events over time, rather than any one risk factor, that determines outcome.

The strongest evidence of genetic influence on depression comes from twin studies. Researchers look at individuals with identical genetic makeup but different environments, namely twins from the same egg who have been reared apart from each other. In such unusual pairs, when one of the twins develops manic-depressive disorder, the other does about 70 percent of the time. This indicates a strong genetic predisposition. On the other hand, this also means that even with an identical genetic makeup, 30 percent of the time the other twin did not become ill. Looking at severe, recurrent, long-standing depression without mania, the same kind of studies show that 50 percent of the time the other twin does not become ill.

Once again, biology is not destiny.

The most we can say is that when there is no set of adversities associated, depressions do cluster in some families - but even for those with such histories, this does not mean that all members will become depressed. Rather, it means that the chance of becoming depressed increases by 5 to 20 percent compared to those with no family history.

The most comprehensive of the recent genetic studies, conducted by Dr. Kenneth Kendler, affirmed again the balance of genetics and adversities in depression. He and his colleagues followed groups of young women, some of whom were related to one another genetically (e.g., identical twins, fraternal twins, and siblings), and some not. He also looked at the adversities they'd undergone, such as suffering traumatic loss as well as prior depression. All of the known influences taken together could explain only about half the cases of depression. The work also confirmed both the importance of recent traumatic events and genetic factors. Kendler himself emphasizes that although studies can demonstrate broad categories of influence, it is not possible to estimate with certainty how to apply this to the risk in any given individual's life - an important caution that again emphasizes that depression is not inevitable.

Childhood depression has been recognized as a distinct illness only recently, and how genes figure in it is still almost unknown. Studies of families of children who have experienced long-standing depression do show that there is more of a family history of depression than in families where there is no childhood depression. But even so, most families in which childhood depression occurs do not have an extensive history of depression, so it's simply not correct to draw conclusions about genetic influence.

Focusing on genetics tends to obscure other essential truths for those worried about depression in their families. Once again, just as there are risk factors, there are protective factors, the resources and strengths that make depression less likely, or at least less severe.

Early treatment can be one such protective factor. So can having close, intimate, confiding relationships, whether it is a marriage, a friendship, or a bond with a sister or brother.

Just as being in a difficult job can predispose you toward depression, so being able to work and get pleasure and satisfaction from a job can protect you.

Because depression is influenced by so many factors - losses and adversity, a family history of the disease, a tendency to fixate on the negative - the best models for understanding the cause of the illness are interactive, meaning they take into account different factors, how they balance one another, and how they affect one another over time.

Whenever there is a risk, both protective forces and adversities have much to say about who gets depressed and who doesn't. The same is true for genetic and social risks. Studies by the sociologist Dr. George Brown have shown, for example, that a risk factor such as the death of a parent in childhood leads to depression in adulthood only when the individual lacks the protective resources of close friendships and/or a satisfying work situation, and faces a stress in adulthood.

Bottom line: The best we can say is that it is the assembly of events over time rather than any one risk factor that determines outcome.

Or, put another way, we can say that:

1. In the psychological sense, depression is being overwhelmed and coming to feel helpless and hopeless, almost always because of certain events.

2. In the social sense, depression is both an interpersonal disorder and a family illness.

3. In the biological sense, depression represents a profound change in usual functioning, a change that is somewhat more likely in some families than others.

All three perspectives concur in emphasizing that depression, once it occurs, is a devastating illness, and that the presence of depression itself will further complicate the lives of those who suffer from it. Having one depression may even change the underlying biology of the brain to increase the vulnerability to later depression, in a process called "kindling."

We can draw two important conclusions: First, once again, that biology is not destiny, and second, that it is vital to build the positive resources of children and families so as to try to prevent depression in children, or, when that is not possible, to intervene very intensely early in its course.

As you will see throughout the rest of this book, the single most important area to focus on in protecting you, your spouse, and your children is promoting healthy and open relationships within the family and among extended family, friends, and the larger community.

In the next chapter, I address treatment interventions. Then I will turn to promoting the open communication described above, as well as other steps you can take to minimize the risk of depression occurring in those you love.