question: Bipolar disorder (Causes): The exact cause of bipolar disorder is unknown, but several factors may be involved, such as: - Biological differences. People with bipolar disorder appear to have physical changes in their brains. The significance of these changes is still uncertain but may eventually help pinpoint causes.   - Genetics. Bipolar disorder is more common in people who have a first-degree relative, such as a sibling or parent, with the condition. Researchers are trying to find genes that may be involved in causing bipolar disorder.