Data shows that the risk increases the more closely related you are to the person with the disorder. If you have a first-degree relative (mother, father, sister, or brother) with bipolar disorder, you have roughly a 15 percent chance of developing it. If both parents have bipolar disorder the probability goes up to between 30 and 50 percent.
If you also have brothers and sisters with the disorder, the likelihood increases. The chance of developing bipolar disorder diminishes the more distantly related you are to the family member who has it. The likely reason for this is that the further away you are, in terms of the direct blood line, the less genetic material (DNA) you have in common with a particular relative.