We analysed Stroop (neuropsychological screening test) measures of response
inhibition in 18 twin pairs discordant for bipolar I disorder compared with
17 healthy control pairs, as well as 40 singletons with bipolar disorder
with psychotic features and a family history of psychosis, 46 of their
first-degree relatives without bipolar disorder or psychosis and 48
controls. In both studies, individuals with bipolar disorder showed Stroop
deficits and their first-degree relatives showed intact performance. In the
twin patients, an interference score was associated with depressive
symptoms. Having a first-degree relative with bipolar disorder, even a
familial, psychotic form, did not confer risk for enhanced susceptibility to
interference in our studies.