Causes of Bipolar Disorder
There are three senses in which bipolar disorder can be said to be caused. The first sense is whether or not the disease is genetic or caused by the environment. The second is what causes the onset of bipolar disorder. The third sense is what exactly is going on in the brain to cause the symptoms of bipolar disorder.
At present, for all three senses, the evidence is not completely conclusive. First, there seems to be a combination of genetic and environmental factors involved in the generation of the illness. While recent research leans more heavily toward genetic factors, there still appears to be a “remainder” that can only be attributable to the environment. Second, onset of bipolar disorder seems to be tied with stress or the use of anti-depressants in many people, but others develop the disorder without such triggers. Finally, what exactly is going on in the brains of bipolar people is controversial in itself. Recent work in imaging has provided more information on this subject.
What arises is a developing picture of bipolar disorder, including its sources and its physical nature in the brain. In this article, I will discuss all three types of causes and the different factors within them.
Question One: Is Bipolar Disorder Genetic?Until recent years, the common wisdom was that bipolar disorder was only partly genetic. On the one hand, it had been discovered that people with bipolar disorder always seemed to have someone with bipolar disorder somewhere in their family. On the other hand, even identical twins appeared to only share bipolar disorder with their twins a little more than half of the time. It therefore seemed to be something of a mixture of the two causes. There appeared to be some sort of genetic disposition, but there was something environmental that would trigger the bipolar disorder itself.
However, in 2004, there was a major twin study published in The American Journal of Psychiatry. The study noted that previous studies had made a serious error in establishing the connection between twins. In most studies, two identical twins were simply asked whether or not they had ever been diagnosed with bipolar disorder. The problem with making conclusions about heritability from studies using self-reporting is that they leave out the possibility that one twin may have bipolar disorder and simply never been diagnosed. Instead, the AJP study conducted personal interviews with twins using a standard questionnaire called the “Structured Clinical Interview for DSM-IV Axis I Disorders”. The conclusion was that bipolar disorder is 93% attributable to heritable factors.
This, of course, is a major shift from the traditional understanding. In fact, it is even possible (though not necessary) that the remaining 7% is the result of errors in the study and that bipolar disorder is simply completely genetic. The overlap in identical twins is simply much higher than was previously thought.
Note that this does not imply that bipolar parents will therefore have a 50% chance that each of his or her children is bipolar. Outside of identical twins, heredity is far more complicated than that. Any “recessive” elements of the disorder will lower the overall rate of transmission. Transmission rate estimates vary from study to study, but range from a 4% to 15%. However, if both parents are bipolar, the chances of having bipolar disorder will increase above 50%. In as much as bipolar disorder is genetic, at least some components of the disorder are recessive.
Question Two: What Causes the Onset of Bipolar Disorder?
Bipolar disorder, however, isn’t simply caused in the sense of genetics and environment. Bipolar disorder also has what is called an “onset”. At some point in a person’s life, people who have the bipolar genes have their first episode of the disorder. Often times, this first onset is especially severe. What is interesting is that, despite bipolar disorder’s being almost entirely heritable in the genetic sense, most people with bipolar disorder don’t simply become manic at random. Instead, there are standard triggers that bring about the “onset” of the disorder, which is the first of usually many episodes.
Trigger One: StressMany people who have bipolar disorder have reported that their first bipolar episode occurred at a time of extreme stress. This can include a major transition in their lives, such as moving to a new city, starting university, getting a divorce or having a death in the family. Rather than have the typical emotional responses to the stressful event or time, an either manic, hypomanic or major depressive episode is triggered. Especially in the case of those with Bipolar I, this first episode can be unusually severe. At this point, the person with bipolar disorder will began to have episodes on a fairly regular basis.
Trigger Two: Antidepressants
One of the biggest mistakes made in medicine generally and in psychiatry specifically in the last twenty years is the prescription of antidepressants to patients having major depressive episodes before ruling out the possibility of bipolar disorder. Many antidepressants can cause mania in those with bipolar disorder, even those who only have bipolar 2 (a manic episode caused by medications would not qualify a person with bipolar 2 for having a bipolar 1 diagnosis). This is especially true of those who have rapid cycling bipolar disorder. After having a manic episode on the antidepressant, the patient is then diagnosed as being bipolar.
Many people people with bipolar disorder report that they had their first onset of the illness after having taken an anti-depressant. This, of course, is a recent source of onsets.
Are These Triggers Causing Bipolar Disorder?
One of the largest controversies in the study of bipolar disorder today is whether or not stress and antidepressants are a part of the ultimate cause of bipolar disorder or whether or not anyone with a disposition to bipolar disorder would have simply had something else trigger their first onset later on anyway.
- School One: People have only a genetic predisposition to bipolar disorder, and then that disposition may or may not be triggered by stress or an antidepressant. Had the person avoided that particular stress or that antidepressant, that person may have avoided the onset of bipolar disorder entirely.
- School Two: The predisposition to bipolar disorder is so strong that is really a predetermination and that onset is inevitable. While a given stressor or antidepressant triggered the onset of the disorder, had that not been the case, some other trigger would have triggered the onset later. This is the standard view
This debate is especially prevalent when it comes to antidepressants. There are some like Dr. Wes Burgess, author of The Bipolar Handbook, who argue that many cases of bipolar disorder are caused and not simply triggered by antidepressants, and this explains why there has been such a rise in bipolar disorder diagnoses in the last fifteen years. Others argue that twin studies show that bipolar disorder is genetically predetermined, and that antidepressants, while dangerous in so far as manic episodes are dangerous, are not actually causing the disorder.
Unfortunately, without time machines, this debate may not be resolvable (unless bipolar disorder is definitively proven to be completely predetermined).
What is Happening in the Bipolar Brain?
The third sense in which something can be said to cause bipolar disorder is what is happening in the brain to make it a bipolar brain rather than a non-bipolar brain. Unfortunately, there is no scientific consensus as to what is actually occurring in the bipolar brain that leads to its characteristic cycle of episodes. The most common theory is the chemical imbalance theory, and this theory has guided understanding of bipolar disorder, major depression and other mental illnesses.
The Chemical Imbalance TheoryIn 1949, a man named Maurice M. Rapport discovered the chemical structure of a neurotransmitter that he and two other scientists had named “serotonin”, allowing for it artificial production. Two years earlier, LSD had first been manufactured by a company named Sandoz Laboratories. It became clear quickly that LSD and serotonin had fairly similar chemical qualities. In addition, LSD had significant effects on mood. It therefore was hypothesized that serotonin has a great deal of effect on mood.
From that point, psychopharmacology really took off. For those with mood disorders, mood could be affected directly by influencing the amount of serotonin in the brain. Conversely, many disorders of the mood were hypothesized to be themselves disorders of serotonin. Over time, two other neurotransmitters, norepinephrine and dopamine, were discovered to be associated with mood.
There are variations on the chemical imbalance theory, but they have the same basic structure. Either the absolute or relative amounts of these transmitters is somehow incorrect. This imbalance leads to very high and very low moods, which in turn can be treated pharmacologically by substances that restore the correct levels of these neurotransmitters.
This theory has the advantage that it explains some of the results of MRIs on bipolar brains, which show that those with bipolar disorder have excesses of up to 30% of certain neurotransmitters in their brains. Certainly, it would appear that neurotransmitters have something to do with bipolar disorder. It also explains why medications that affect serotonin and other neurotransmitters seem to have effects on those with bipolar brains (even if those effects are very bad, as can be the case with antidepressants).
The downside of this theory is that it doesn’t really explain where the chemical imbalances are coming from, or why it is that they cycle in the way that they do. In a sense this is the discovery of a cause, but almost in the sense of saying that “the cause of a bent limb is a broken bone”. It doesn’t really get at the root of the issue. In addition, it doesn’t really explain why mood stabilizers, which don’t directly manipulate seratonin and other neurotransmitters, have positive effects on those with bipolar disorder.
Summing It Up
Bipolar disorder has different types of causes, and all of those types of causes are controversial.
- Genetic Versus Environmental: Recent twin studies seem to indicate that genetic causes are substantial in bipolar disorder, but there is still debate.
- Triggers: Bipolar disorder usually has its first onset as the result of stress or the use of antidepressant medications.
- The Brain: Bipolar disorder in the brain seems to be connected to neurotransmitters in the brain, though there is still debate about how exactly this connection works.