Bipolar disorder and heredity

If a woman has a sister with bipolar disorder (and no other family history of mental health problems), and she marries a man with no family history of mental health problems, what are the chances that their children will have bipolar disorder?

Thanks, J

[Roger Gould, M.D.]

The chances are very small, and probably no greater than random, especially since the diagnosis of bipolar has many levels, and often many errors.

[jaybee12]

It seems like the sister's diagnosis is pretty convincing (I am not a psychiatrist, but I am a physician and I have spoken with her psychiatrist, and personally observed her in a manic state with psychotic features, alternating with nearly catatonic depression).  Does this increase the odds, or would you say they are still low and close to random?  Thanks.