Is Depression Hereditary?
With a more open attitude toward mental illness come greater investigations into depression and its causes, including the question: is depression hereditary? If a parent or sibling has suffered from depression of some sort, other family members sharing the same blood are understandably concerned that they may also endure depression at some time in their lives. When family members witness and/or support a person with depression, it is logical that they should fear it for themselves. But is depression really a part of genetic make-up?
Medical research tells us a little and conversely a lot, but what we do know is fairly general. Depression is not regarded as a primarily biological disorder of the brain. While this may seem like a narrow statement, it is also broad and all-encompassing. By its sheer ambiguity, it distills into one sentence what all research to date points towards. Depression may be somewhat hereditary and somewhat environmental, but it is not inevitable.
What Proof Exists that Depression is Hereditary?
Psychiatrists acknowledge that depression tends to run in families, and yet there are plenty of examples where two clinically depressed parents can produce a child free from depression. What there seems to be is a general tendency toward depression within certain families; whether that is purely genetic code or not remains to be proven, but here are some facts about hereditary depression:
- Pregnancy in women is a common source of depression, due in large part to vast hormonal fluctuations. Doctors believe that it is possible a fetus may inherit depression from a depressed mother. That is not to say the baby is born with depression as a result; this is not akin to something like fetal alcohol syndrome. Still, there may be depressive hormones transferred.
- Our genetic code (DNA) predisposes us to certain diseases and there is no reason why depression may not be part of that.
- Clinical studies established to separate a specific gene that causes depression have proved inconclusive, but research continues.
Bipolar disorder is one of many forms of depression and for some reason it seems to be more traceable to genetic make-up. For example, a person with a parent or sibling who has been medically diagnosed as having bipolar disorder (manic depression) is 3 times more likely to develop the condition than a person with no first-line blood relatives that have it. The child of two bipolar parents has up to a 75% chance of developing it. Odds are 50% that a person with bipolar disorder has a parent or sibling who suffers from it also.
Most clinical medical studies on the heredity of depression involve a link with another disease. For instance, hereditary depression among siblings where cancer has played a dramatic role throughout their family lives. Rarely is a study undertaken with satisfying conclusions that relate strictly to the question: is depression hereditary?
A study by Serbian researchers performed in a university setting examined “the hereditary burden for the depressive disorder”. This study acknowledges the complexity and breadth of the subject, and specifically addresses depressive disorder, as opposed to other forms of depression, including bipolar disorder; it can be read in-depth at: www.ncbi.nlm.nih.gov/pubmed/19368290. In short, the article based on the study concludes: “The research showed the influence of aggregation of psychiatric disorders in families on the onset and severity of depressive disorders. The interaction of genetic and psychosocial factors has been confirmed in the etiology of depression.”
Still, this is not completely conclusive of an on-going link between genetic make-up and depression. Clearly, there is at this time no hard evidence that depression is primarily or even directly hereditary, and yet there are studies that show a proclivity to it. By studying identical twins (the only people that share an identical genetic code), researchers have been able to reveal a pattern that suggests, but also leaves open to question, the correlation between genes and depression. Here is what the studies of twins and their connection to hereditary depression tells us:
- That identical twins, with exactly the same genetic code, who also live in the same environment both develop depression about 75% of the time.
- That identical twins who were raised separately and live in different environments (perhaps even different countries and have no relationship with one another) both develop depression about 65% of the time.
- That fraternal twins (who have similar, but not identical genetic make-up) may develop depression in 50% of cases.
This demonstrates a propensity toward developing depression within a hereditary framework, but it also leaves a huge gap: what are the other factors?
Other Influences That Affect Depression Within Families
Until further extensive research is performed, what we know about hereditary depression is rather vague, and posits that genetic code and environment have a combined influence, if not a 50/50 contribution. What scientists believe is that having depression within the genetic code can predispose certain, but not all, people, to developing clinical depression within their lifetimes. It is the vulnerability to depression that is key, not the actual onslaught of it. When vulnerability is present, and external factors such as trauma or life crises arise, the predisposition may serve to drive some individuals into a clinical depression. Still, others within the same family and with shared blood will not necessarily react in the same way.
Living in a household with a depressed parent, for example, can set the tone of life for a child. What he or she sees as “normal” behavior in what is in fact a clinically depressed parent may influence the child’s behavior in later years and serve as an effective example of how to live. The depression appears normal and the depressed environment is confirmed as normal to a child.
The other point of interest is that even in a household with two depressed parents and other depressed siblings, one or more of the other children will apparently waltz through life without any signs of depression whatsoever. It may be they who carry the tone of the home, staying exceptionally upbeat and ensuring (albeit unwittingly) that the environment is not entirely depressed. What needs further study is to discover if these non-depressed offspring are actually exempt from depression or if they are in some way suppressing it in the better interests of the family.
Existing research tells us that even in depressed families, with one or more members suffering clinical depression, other members will not automatically become depressed. Researchers and psychiatrists agree that simply by observation they know depression tends to run in families, but as yet there is no conclusive proof that depression is hereditary.