Similarly, the risk of bipolar disorder was 24.9 percent in 146 offspring of 83 parent couples who were both admitted for bipolar disorder (increasing to 36 percent when unipolar depressive disorder was also included). This compared to a risk of 4.4 percent among 23,152 offspring of 11,995 couples with only one parent ever admitted for bipolar disorder and 0.48 percent in 2.2 million children of 1 million couples with neither parent ever admitted.

When one parent had bipolar disorder and the other had schizophrenia, offspring had a 15.6 percent risk of schizophrenia and an 11.7 percent risk of bipolar disorder.

The risks in this population "are of such a magnitude that they command clinical and national public health attention in countries with health care roughly similar to Denmark's," the authors write.

"It is important to keep in mind that the yields from genetic epidemiology and the strategies implemented are applicable to groups of people, not to the individuals themselves," they conclude. "However, by joining advances in molecular genetics that are adapted for use in epidemiological genetic screening, our kinds of data with the risk groups described might lead to a large and rapid step forward in the understanding of the etiologies of major mental disorders."

SOURCE Archives of General Psychiatry