A lifetime prevalence of bipolar I disorder in community samples ranges from 0.5 to 1.5% That is to say 5 to 15 people per thousand of the population ‘at large’ might develop bipolar type 1 disorder. This rises to 4-9% in their first degree biological relatives (i.e. their immediate family).
There is also a raised rate of bipolar II disorder (1-5%) and major depressive disorder (8-20%) in these relatives. Twin and adoption studies (which are often used to ‘determine’ the heritability of a feature or trait) suggest that a significant proportion of the risk of bipolar disorder is genetic.
Due to the absence of a reliable genetic or an early foetal marker, genetic counselling is limited to providing information on these risks.