A twin study of normative personality and DSM-IV personality disorder criterion counts; evidence for separate genetic influences

Background: Normative personality and DSM-IV personality disorders (PD) have both been found to be heritable, but the extent to which they share genetic influences is largely unexplored.  Methods: 2,282 Norwegian twins were... [ view full abstract ]

Background: Normative personality and DSM-IV personality disorders (PD) have both been found to be heritable, but the extent to which they share genetic influences is largely unexplored. 

Methods: 2,282 Norwegian twins were assessed for DSM-IV criteria for personality disorders using structured interviews. Ten years later years the twins were re-interviewed, and normal personality was assessed using the Big Five Inventory. The amount of genetic variance that DSM-IV PD criterion counts had in common with the domains of the Big 5 was estimated by means of multivariate Cholesky twin decompositions. 

Results: While the heritability of the number endorsed criteria for the personality disorders ranged from 0.2 to 0.41, the proportion of genetic variance that was unique to each PD ranged from 19% for Avoidant to 79% for Schizotypal (median of 58%). Conversely, the proportion of environmental variance unique to the personality disorder criteria ranged from 79% to 99 (median 97%). 

Conclusion: A considerable proportion of the genetic variance and virtually all environmental variance is unique to the personality disorders, and not shared with the five broad domains of normal personality.