ERBB4 and major depressive disorder: Variation in ERBB4 has been reported in association with serotonin metabolite levels59, the openness personality trait of the five-factor model60, neuroticism61–63, positive affect/wellbeing63, intelligence64,65, educational attainment62, cognitive function37, loneliness/isolation/social interaction66–68 and depressed affect/unipolar depression/mood disorder61.