Update on research into the genetics and pharmacogenetics of bipolar disorder

Bipolar disorder (BD) is a severe mental disorder that is characterized by recurrent episodes of mania, and depression. The phenotypic expression can be complemented by suicidal behavior, psychosis, comorbid anxiety, substance abuse, and rapid cycling (1). With a prevalence of ~1% and high risk of morbidity, it is a major health problem (2). BD has been shown to be a highly heritable disease, with concordance rates being ~85% within twin studies (3). As in other psychiatric disorders, polygenic components have a role in the liability of the disorder. The combination of both genetic and environmental effects influence the risk of developing the disorder. Up to date, there have been several studies of BD including linkage analysis, candidate gene studies, and genomewide association studies (GWAS). Moreover, it has been established that there is a genetic correlation between BD and schizophrenia conferred by common genetic variation, so called single nucleotide polymorphisms (SNPs), suggesting a shared genetic etiology between these diagnostic entities (4). Yet, our knowledge of the role of genetic factors in susceptibility of BD is still limited. Given the fact that BD is a highly heterogeneous disorder, studies with more homogenized groups that gather samples with more specific properties, such as subphenotypes of BD or patients positively responsive to specific drug treatments, may help improve the efficiency of studies. Main challenges in the treatment of BD, as in other disorders, are the differences of response to treatment within patients. Furthermore, adverse events and metabolic conditions caused by mood stabilizers and/ or antipsychotic drugs can affect the treatment procedure of a patient (5).