Personality disorders are thought to be caused by an interaction between genes and environmental factors during the early years of development. Growing up in single-parent and stepfamilies, young motherhood, maternal depression and financial problems in childhood have all been considered as risk factors for children's mental health. A Finnish study of 1,588 young adults looked into the links between family structure and the later development of personality disorders. 7% of the participants had at least one probable or definite personality disorder. After adjusting for gender, parental social class and parental psychiatric disorder it was found that coming from a single-parent family was associated with cluster B (antisocial, borderline, histrionic and narcissistic) personality disorders while being an only child was associated with cluster A (paranoid, schizoid and schizotypal) disorders.
Kantojarvi, L. ... [et al] - Childhood family structure and personality disorders in adulthood European Psychiatry 2008, 23, 205-211