Though definately a genetically influenced disease, researchers have begun to learn a lot about some other possible causes.
Bipolar disorder tends to run in families, and is believed to be inherited in many cases. More than two-thirds of people with manic-depressive illness have at least one close relative with the disorder, or with major depression. This suggests that genetic factors are important, and it is likely that susceptibility to the illness is related to several genes. However, the specific genes involved have not yet been conclusively identified. Once this is achieved it is hoped that it will be possible to better treatments and prevention strategies aimed at the underlying illness process.
It may be that the development of bipolar disorder is due to a process of sensitisation (kindling). This idea suggests that the first episodes of illness are triggered by stressful life events, but that each episode of illness causes changes in the brain which make the next episode more likely, and eventually episodes occur spontaneously. This process was first describes as an explanation for epilepsy, and may explain why certain antiepileptic drugs are also effective in the treatment of bipolar disorder.
Neurotransmitters are the molecules that enable the transmission of nerve impulses from one nerve to the next. Since it is thought that faulty nerve transmission may be one cause of bipolar disorder, it is possible that these molecules are involved. Examples include dopamine, serotonin (5-HT; 5-hydroxytryptamine), acetylcholine, GABA and glutamate.