There are a couple of factors that could be involved, such as biological differences. People with bipolar disorder appear to have physical changes in the brain. The meaning of these changes is still uncertain but could possibly help in some way to identify the causes. There are also neurotransmitters that are imbalances in the brain's natural chemicals called neurotransmitters that appear to play a significant role in bipolar disorder and other mood disorders. 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 might be involved in causing bipolarity