Scientists don't know the exact cause of bipolar disorder. Still, many experts believe that of all psychiatric disorders, bipolar is the most closely linked to genetics. For example, if your parent has bipolar disorder, you are about nine times more likely to get the condition than teens with no family history. Biochemical and environmental factors play a role in bipolar disorder, too. In fact, researchers think that imbalances in neurotransmitters (brain chemicals that regulate moods) increase the chance of bipolar disorder.