Causes

What Causes Bipolar Disorder?

Much like other mental illnesses, there isn’t an exact cause for bipolar disorder, but rather, a multitude of factors that interact with each other. There may be a genetic component to the illness as researchers have discovered that it has a tendency to run in families. Experiments have been conducted to try to isolate one or several genes responsible for the inheritance of bipolar disorder. In a study done by Dr. Gábor, brain samples were used to study possible mutation of genes. By studying the interaction between the enzymes produced by these genes, he may be able to estimate the genetic risk for bipolar disorder.

Another common method is to study the brain for possible irregularities. Noninvasive procedures like MRI (magnetic resonance imaging) PET (positron emission tomography) and fMRI (functional magnetic resonance imaging) show that brains of bipolar patients may differ from those without bipolar disorder. For example, neurotransmitters (chemicals used to transfer signals between neurons and cells) have been of great interest to bipolar disorder researchers. This is because when bipolar patients are administered drugs that reduce or increase levels of certain neurotransmitters, their condition is sometimes alleviated. Therefore, there is a theory that mood disorders and neurotransmitters are somehow linked (specifically, serotonin, norepinephrine and dopamine). However, researchers disagree over whether it is too much or too little of one neurotransmitter or just an overall imbalance of all the neurotransmitters.

However, it is unlikely that genetics is the sole factor. For example, in the case of identical twins, if one twin has bipolar disorder than the other twin will be more likely (than another sibling of the same family) to develop bipolar disorder. The actual rate for a concordance (when both twins develop bipolar disorder) is about 80% for identical twins versus 16% for fraternal twins. However, the other identical twin will not always develop bipolar disorder meaning there really isn’t one gene that is responsible for bipolar disorder. That being said, when one family member has bipolar disorder, his or her first-degree relatives (parents, children, siblings) are more likely to develop mental illnesses related to mood swings.

In recent studies, the mitochondria (the “powerhouse of a cell, it generates energy) has also been linked to the onset of bipolar disorder. In one study, several mice were genetically engineered to dysfunctional mitochondria within their brain cells and demonstrated typical symptoms of bipolar disorder. For example, their circadian rhythm (activities done within a daily cycle) was disrupted. These mice also responded to treatment in the same manner a bipolar patient would. Lithium alleviated their symptoms whereas antidepressant medication worsened their symptoms.

One must also take in account the environment that the patient was brought up in as well as their genetic background. Traumatic life events such as abusive childhoods, divorces or the death of a loved one are some of several environmental factors that could lead to bipolar disorder. Sometimes, the onset of puberty can be a trigger for the first manic or depressive episode especially when girls go through their menstrual cycle.