This is a problem not only for the genetics of PDs, and the search for better phenotypes for genetic studies of mental disorders is especially well illustrated in the

literature on schizophrenia (eg, refs 5, 6). The goal of psychiatric genetic epidemiology is to understand the role of genetic and environmental factors in the etiology of mental disorders.7 In this paper we will focus mainly on the genetic factors. After a brief outline of the current DSM axis II Inhibitors,research,lifescience,medical PD classification, we will evaluate the evidence for genetic influences on PDs and examine quantitative genetic studies that explore the specificity of the genetic effects, ie, to what extent genetic risk factors are shared between PDs, or between PDs and axis I disorders.

Molecular genetic studies that aim to identify gene variants associated with PDs will then be reviewed. It is likely that PDs, Inhibitors,research,lifescience,medical like most other psychiatric disorders, are etiologically complex, ie, that they are influenced by a number of genetic and environmental risk factors. Studies examining the interplay between genes and the environment will be addressed both in relation Inhibitors,research,lifescience,medical to quantitative and molecular methods. Finally, future directions will be discussed. The classification of personality disorders A PD is defined by DSM-IV as an enduring pattern ofinner experience and behavior that deviates markedlyfrom the expectations of the individual’s culture, is per-vasive and inflexible, has an onset in adolescence orearly adulthood, is stable over time, and leads to distressor impairment.8 The DSM-IV classification

includes 10 categorical Inhibitors,research,lifescience,medical PD diagnoses grouped into three clusters: A or the “odd-eccentric,” B or the “dramatic-emotional,” and C or the “anxious-fearful.”8 Cluster A includes para-noid, schizoid, and schizotypal PD, and Cluster B anti-social, borderline, histrionic, and narcissistic PD, whilecluster C includes Selleck Blebbistatin avoidant, dependent, and obsessive-compulsive Inhibitors,research,lifescience,medical PD. Appendix B includes two additional dis-orders: depressive and passive-aggressive PDs. Although the classification of PDs in DSM-IV is moreempirically based than in former versions, there are several controversial issues that are unresolved. Substantialco-occurrence between the DSM PDs has consistentlybeen found in both clinical9and community samples.10,10The majority of individuals with a PD receive more thanone PD diagnosis, and this high degree of overlap seri-ously Thymidine kinase challenges the descriptive validity of the PD classification. Comorbidity with Axis I disorders is alsoextensive, and results from both clinical and population-based studies indicate that the key features in the DSM-IV definition (stability over time and early age of onset)do not distinguish PDs from axis I disorders.12 Theunderlying validity of the DSM axis I – axis II divisionhas therefore been questioned (eg, refs 12-14).