Abstract
Impulsivity is elevated in psychosis and during mania in bipolar disorder. Studies in unaffected relatives may help establish whether impulsivity is a heritable, state independent endophenotype. The aim of this systematic review and meta-analysis was to examine whether impulsivity is elevated in unaffected relatives of those with bipolar disorder, schizophrenia, and schizoaffective disorder, compared to controls. Databases were systematically searched up until March 2023 for articles reporting data on a behavioral or self-report measure of impulsivity in first-degree relatives and controls. Nineteen studies were included. Behavioral (10 studies, d = 0.35, p < 0.001) and self-reported impulsivity was significantly elevated in bipolar disorder relatives compared to controls (5 studies, d = 0.46, p < 0.001), with small effect sizes. Relatives of those with schizophrenia did not show significantly elevated impulsivity compared to controls on behavioral measures (6 studies, d = 0.42, p = 0.102). There were not enough studies to conduct a meta-analysis on self-report data in schizophrenia relatives or schizoaffective disorder relatives (self-report or behavioral). Study quality was good, however there was moderate to high heterogeneity in behavioral meta-analyses. Results suggest elevated impulsivity may be an endophenotype for bipolar disorder, present in an attenuated state before and after the illness and in at-risk individuals. This trait, amongst other behavioral and psychological indices, could be used to identify those who are at risk of developing bipolar disorder. Future research should refine measurement across studies and establish which components of impulsivity are affected in those at risk of psychotic and bipolar disorders.