Objective: Impulsiveness is a heritable feature of borderline personality disorder (BPD) which aggregates in families affected with the illness. Whereas BPD patients show deficits on neuropsychological tests of response inhibition, it is unknown whether these deficits are also present in their first-degree biological relatives who are at an increased genetic risk for this illness. The purpose of the current study was to identify and characterize a subgroup of BPD patients with pronounced response inhibition deficits, and secondarily, to estimate the relative recurrence risk of these deficits among affected families. Method: Thirty-nine pairs of female BPD probands and their unaffected first-degree biological sisters were recruited from hospital outpatient clinics. Participants completed the Conners' Continuous Performance Test (CPT) and the Barratt Impulsiveness Scale-11. Results: BPD relatives made a similar number of commission errors on the CPT compared to healthy controls with no personal or family history of psychiatric illness; however, cluster analysis revealed a subgroup of BPD relatives who displayed clinically elevated commission errors and atypically fast RTs to target stimuli, indicating a genuine response inhibition deficit. The estimated relative recurrence risk for response inhibition deficits for all sibling pairs on the CPT was moderate at ? = 4.55. Conclusions: These findings suggest that response inhibition deficits are pronounced in some BPD relatives, may be heritable between siblings, are nonredundant with diagnostic status, and show promise as candidate neuropsychological endophenotypes for BPD.
