Evidence of disrupted prepulse inhibition in unaffected siblings of bipolar disorder patients

Background: Prepulse inhibition (PPI) of the startle response refers to a reduction in the response to a strong stimulus (pulse) if preceded shortly by a weak stimulus (prepulse). Disrupted PPI is thought to reflect abnormalities in the inhibitory control of information processing. Reduced PPI has been reported in mania, although it is not clear whether it represents a trait feature of bipolar disorder (BID). To address this issue, the present study examined whether disrupted PPI is present in individuals at high risk for BID. Methods: Twenty-one remitted BID patients and 19 of their unaffected siblings were compared with 17 age- and gender-matched healthy volunteers on tests of acoustic startle reactivity and PPI of the startle response. Results: There were no group differences in startle reactivity. Compared with healthy individuals, BID patients and their unaffected siblings showed lower PPI. In the patient group, no significant correlations were found between PPI and measures of symptom and disease severity or medication. Conclusions: This is the first study to report reduced PPI in remitted BD patients and their unaffected first-degree relatives. This finding, although in need of replication, suggests that PPI disruption may represent a trait deficit in BID associated with genetic predisposition.