Risk of Bipolar Disorder Associated with Enhanced Verbal Ability and Positive Social Traits
A recent twin study suggests that the genes that confer risk for bipolar disorder may also be associated with verbal ability and sociability. Considerable evidence has suggested that people with bipolar disorder have greater intelligence and creativity than the normal population. Positive qualities like these may make people with bipolar disorder attractive mates, leading to the continued propagation of genes that promote bipolar disorder. (One might expect lower than normal rates of reproduction in people with bipolar disorder due to the difficulties the illness creates, as occurs with schizophrenia, but people with bipolar disorder have normal rates of reproduction, suggesting that any obstacles to mating are balanced by other particularly attractive qualities.)
Researchers led by Rachel G. Higier used a Swedish registry of twins to investigate whether people with bipolar disorder and their fraternal or identical twins without the illness have better verbal ability and sociability. Bipolar patients and their twins (who would be expected to have similar genetic and familial risks but without the negative impact of the illness and medications for it) were compared to patients with schizophrenia and their twins and normal controls. The well twins of bipolar patients scored higher on a scale of positive temperament than the bipolar patients, schizophrenia patients and their twins, and controls. The twins of bipolar patients also scored better than schizophrenia patients and their twins and controls on tests of verbal learning and fluency, while the bipolar patients showed lower levels of cognitive function (likely due to their illness).
The researchers conclude that the genes that put families at risk for bipolar disorder also confer positive traits like verbal ability and positive temperament that make people with bipolar disorder attractive mates. Even though bipolar disorder may reduce these traits somewhat, people with the illness still are more creative than the general population and often very successful.
