Genetics
Although researchers do not currently understand exactly what causes bipolar disorder, it is commonly thought that there is a genetic component. According to the National Institute of Mental Health, people who have a sibling or parent with bipolar disease are four to six times more likely to develop bipolar disease themselves. According to the Mayo Clinic, researchers have also identified some genetic linkage between bipolar disorder and schizophrenia, which suggests that there is an underlying genetic defect that can predispose patients towards both. Studies to determine exactly what these genetic problems are, however, have not been conclusive.
Biochemical
Researchers have also noticed that there are differences in the brain's structure and chemical makeup in people with bipolar disorder. According to the Mayo Clinic, although scientists don't know what role these brain changes play or how they occur, physical changes in the brain are thought to be linked to bipolar disorder. Another biochemical factor in the development of bipolar disorder is neurotransmitter levels. Neurotransmitters are chemicals that brain cells use to communicate and differing levels of neurotransmitters have been implicated in bipolar disease, as well as other mental conditions, such as schizophrenia and depression.
Environmental
Although genetics play a role in the development of bipolar disorder, it is clearly not the sole cause. For one thing, the majority of people with a family history of bipolar disorder do not develop the condition themselves. This is even true for monozygotic (identical) twins; sometimes one twin will have bipolar disorder while the other one does not. According to the Mayo Clinic, stress may play a role in the development of bipolar, as can problems with self-esteem and personal loss.
