There were no significant differences in the magnitude of genetic and environmental influences for males and females. In a review of family studies on borderline PD, White et al39 found the disorder to aggregate in families. However, significant methodological problems made the results uncertain. Distel et al estimated that additive genetic factors explained 42% of the variance in borderline PD features assessed by self
Inhibitors,research,lifescience,medical -report questionnaire, using data from three countries.40 Non-shared environment accounted for the rest. In a subsequent extended twin-family study by the same group the heritability of borderline PD features was found to be 45%, but the genetic effects were both additive (21%) and dominant (24%).41 Inhibitors,research,lifescience,medical Nonadditive effects are difficult to detect using the classical twin model due to lack
of statistical power.23 However, such effects have been found for normal personality traits in twin-sibling studies with large samples.42 Results from a twin study based on structured interviews in a clinical sample suggest that heritability estimates for borderline, histrionic, and narcissistic PD were high, 69%, 63%, and 77% respectively.34 More recently, however, Torgersen et al43 conducted a population-based twin study of dimensional PLX3397 purchase representations of the DSM-IV cluster B PDs. Heritability was estimated to be Inhibitors,research,lifescience,medical 38% for antisocial PD, 31% for histrionic PD, 24% for narcissistic PD and 35% for Inhibitors,research,lifescience,medical borderline PD. No shared environmental influences or sex or effects were found. Cluster C A family study of the anxious-fearful cluster indicated significant familiality for DSM-III avoidant and dependent
PD,44 and in a clinically based twin study, heritability estimates for avoidant, dependent, and obsessive -compulsive PD were found to be 28%, 57%, and 77%, respectively34 Results from a population-based Inhibitors,research,lifescience,medical study of dimensional representations of DSM-IV Cluster C PDs,45 however, indicated that heritability estimates were similar for avoidant PD (35%), but lower for dependent (31%) and for obsessive-compulsive PD (27%), again illustrating the importance of method of ascertainment. This discrepancy is probably in part due to difference in methods of ascertainment. No shared environmental MTMR9 effects or sex differences have been found for cluster C PDs. Disorders in Appendix B In a population-based twin study of depressive PD, Ørstavik et al46 found that liability could best be explained by additive genetic and unique environmental factors alone, with heritability estimates of 49% in females and 25% in males. Unlike the results for the other DSM-IV PDs, both quantitative and qualitative sex-differences were found corresponding to findings from studies on major depression.47 Significant familial aggregation has also been found for DSM-IV passive aggressive PD.