Biochemical Endophenotypes in Personality Disorders

Candidate gene association studies in psychiatric disorders have suffered from difficulties in replication. One strategy for overcoming this difficulty is a focus on endophenotypes. If most psychiatric disorders are polygenic and are caused by numerous genes—each contributing a small effect and conferring susceptibility to the phenotype, then it is difficult to identify the influence of each of these genetic contributions to the phenotype. A recent approach, which is the focus of this volume, is the identification of endophenotypes—components of a syndrome that may be influenced by a smaller number of genes and may be more easily associated with a genotype. Other chapters (7,9,10) cover cognitive, electrophysiologic, and neuroimaging endophenotypes. This chapter reviews promising biochemical endophenotypes, using personality disorders as a model.