Making sense of risk figures.
Many people have trouble understanding statements of risk. As you read the risk figures used in this section, try to think about them in different ways. For example, a risk of one percent means one time out of 100. A risk of 14 percent means 14 times out of 100.
You also can turn the figures around. For example, a one percent risk of developing Bipolar Disorder means there is a 99 percent chance of NOT developing the illness. A 14 percent risk for the disorder means the chance of NOT developing it is 86 percent.
The chances of becoming bipolar
The risk to the offspring of two parents who do not have the illness and have no affected relatives is about one percent (1 out of 100).
If one parent has Bipolar Disorder, the risk to offspring is about five percent. It can be as high as 14 percent if other relatives, such as an aunt or uncle, also are affected.
In the unusual case where both parents have Bipolar Disorder, the risk to offspring is approximately 30 percent, but can increase slightly if other relatives are affected.
The siblings (brother or sister) of a person with Bipolar Disorder have roughly an 8 percent risk of developing the illness. The risk increases markedly, however, if other close relatives also are affected. For example, if a person has a sibling and one parent with the disorder, his or her risk rises to about 15 percent
As indicated above, the risk of developing Bipolar Disorder increases with the biological closeness of the relationship. Parents, siblings, and offspring are called first-degree relatives. They have greater risk of being affected than do second-degree relatives such as grandparents, grandchildren, uncles, aunts, nephews, nieces and half-siblings.
It is not as easy to determine risks for common, complex disorders such as Bipolar Disorder, schizophrenia, heart disease, diabetes, and cancer. Clearly, Bipolar Disorder, like other common diseases, often clusters in families. But health-care professionals cannot predict the risk as accurately as they can for single-gene disorders. The difficulty in determining precise genetic risks for Bipolar Disorder results from the complex causes of the disorder, and from our incomplete understanding of how the illness begins.
The figures used above are based on data from large numbers of affected individuals and families. They are estimates only.