Discovery and utilization of haplotypes for pharmacogenetic studies of psychotropic drug response

Epigenetics of psychoactive drugs

Objectives

Epigenetics refers to the heritable, but reversible regulation of various biological functions. Changes in DNA methylation and chromatin structure derived from histone modifications are involved in the brain development, pathogenesis and pharmacotherapy of brain disorders.

Key findings

Evidence suggests that epigenetic modulations play key roles in psychiatric diseases such as schizophrenia and bipolar disorder. The analysis of epigenetic aberrations in the mechanisms of psychoactive drugs helps to determine dysfunctional genes and pathways in the brain, to predict side effects of drugs on human genome and identify new pharmaceutical targets for treatment of psychiatric diseases.

Summary

Although numerous studies have concentrated on epigenetics of psychosis, the epigenetic studies of antipsychotics are limited. Here we present epigenetic mechanisms of various psychoactive drugs and review the current literature on psychiatric epigenomics. Furthermore, we discuss various epigenetic modulations in the pharmacology and toxicology of typical and atypical antipsychotics, methionine, lithium and valproic acid.

Pharmacogenetic of response efficacy to antipsychotics in schizophrenia: pharmacodynamic aspects. Review and implications for clinical research

Pharmacogenetics constitutes a new and growing therapeutic approach in the identification of the predictive factors of the response to antipsychotic treatment. This review aims to summarize recent finding into pharmacodynamic approach of pharmacogenetics of antipsychotics and particularly second generation. Studies were identified in the MEDLINE database from 1993 to July 2008 by combining the following Medical Subject Heading search terms: genetic, polymorphism, single nucleotide polymorphism, pharmacogenetics, antipsychotics, and response to treatment as well as individual antipsychotics names. Only pharmacodynamics studies were analyzed and we focused on efficacy studies. We also reviewed the references of ll identified articles. Most studies follow a polymorphism-by-polymorphism approach, and concern polymorphisms of genes coding for dopamine and serotonin receptors. Haplotypic approach has been considered in some studies. Few have studied the combinations of polymorphisms of several genes as a predictive factor of the response to antipsychotics. We present this gene-by-gene approach while detailing the features of the polymorphisms being studied (functionality, linkage disequilibrium) and the features of the studies (studied treatment(s), prospective/retrospective study, pharmacological dosage). We discuss the heterogeneity of the results and their potential clinical implications and extract methodological suggestions for the future concerning phenotype characterization, genotypes variants studied and methodological and statistical approach.

Pharmacogenetics of antipsychotic response in the CATIE trial: a candidate gene analysis

The Clinical Antipsychotic Trials of Intervention Effectiveness (CATIE) Phase 1 Schizophrenia trial compared the effectiveness of one typical and four atypical antipsychotic medications. Although trials such as CATIE present important opportunities for pharmacogenetics research, the very richness of the clinical data presents challenges for statistical interpretation, and in particular the risk that data mining will lead to false-positive discoveries. For this reason, it is both misleading and unhelpful to perpetuate the current practice of reporting association results for these trials one gene at a time, ignoring the fact that multiple gene-by-phenotype tests are being carried out on the same data set. On the other hand, suggestive associations in such trials may lead to new hypotheses that can be tested through both replication efforts and biological experimentation. The appropriate handling of these forms of data therefore requires dissemination of association statistics without undue emphasis on select findings. Here we attempt to illustrate this approach by presenting association statistics for 2769 polymorphisms in 118 candidate genes evaluated for 21 pharmacogenetic phenotypes. On current evidence it is impossible to know which of these associations may be real, although in total they form a valuable resource that is immediately available to the scientific community.

Pharmacogenetics in psychiatry: are we ready for widespread clinical use?

There are high expectations about the capabilities of pharmacogenetics to tailor psychotropic treatment and "personalize" treatment. While a large number of associations, with generally small effect size, have been discovered, a "test" with widespread use and adoption is still missing. A more realistic picture, recognizing the important contribution of clinical and environmental factors toward overall clinical outcome has emerged. In this emerging view, genetic findings, if considered individually, may have limited clinical applications. Thus, in recent years, combinations of information in several genes have been used for the selection of appropriate therapeutic doses and for the prediction of agranulocytosis, hyperlipidemia, and response to antipsychotic and antidepressant medications. While these tests based on multiple genes show greater predictive ability than individual allele tests, their net impact on clinical consequence and costs is limited, thus leading to limited penetration into widespread clinical use. As one looks at other branches of medicine, there are successful examples of pharmacogenetic tests guiding treatment, and thus, it is reasonable to hope that with the incorporation of clinical and environmental information and the identification of new genes drawn from genome-wide analysis, will improve the predictive utility of these tests leading to their increased use by clinicians.

Individualizing antipsychotic drug therapy in schizophrenia: the promise of pharmacogenetics

The first- and second-generation antipsychotic drugs have become mainstay drug treatment for schizophrenia. However, patients who receive antipsychotic drugs differ with respect to treatment response and drug-induced adverse events. The biological predictors of treatment response are being researched worldwide, with emphasis on molecular genetic predictors of treatment response. Because of the rapid and exciting developments in the field, we reviewed the recent studies of the molecular genetic basis of treatment response in schizophrenia. The accumulating data suggest that DNA information in the pathways for drug metabolism and drug target sites may be an important predictor of treatment response in schizophrenia. The data suggest that clinicians may soon be using a patient's genotype to decide initial choice of antipsychotic drug treatment in schizophrenia. The pharmacogenetics of schizophrenia can improve the prospects of individualized treatment and drug discovery. Pharmacogenetic investigations of schizophrenia susceptibility loci, and genes controlling drug target site receptors, drug-metabolizing enzymes, the blood-brain barrier systems, and epigenetic mechanisms could lead to a molecular classification of treatment response and adverse events of psychotropic drugs.

Haplotype analysis of endothelial nitric oxide synthase (NOS3) genetic variants and tardive dyskinesia in patients with schizophrenia

OBJECTIVES

Several studies have indicated the involvement of nitric oxide (NO) in the pathogenesis of tardive dyskinesia (TD), an incapacitating adverse movement disorder associated with long-term antipsychotic treatment. In human brain, the NO could be generated by endothelial nitric oxide synthase (NOS3). In this study, we studied whether the genetic variants in human NOS3 gene is associated with TD in patients with schizophrenia.

METHODS

Two hundred and eighty-two chronic inpatients with schizophrenia treated with typical antipsychotics were recruited in this study. The patients were further grouped by the presence of TD or not according to the Research and Diagnostic Criteria for TD. The genetic variants in the NOS3 gene investigated in this study were -786T > C in the promotor region, 27-bp variable number of tandem repeats (27-bp VNTR) in intron 4, and Glu298Asp in exon 7. The frequencies of genotypes, alleles and haplotypes of the three markers were compared between the TD (n = 153) and non-TD (n = 129) groups.

RESULTS

There were no significant associations between the genotypes and alleles of the three markers and TD. However, in the haplotype-based case-control analysis, the frequency of haplotype T-4b-Glu was significantly higher in non-TD than in TD group (TD vs. non-TD = 72.7% vs. 81.0%, permutation P value = 0.021, OR = 0.648, 95% CI = 0.432-0.973).

CONCLUSIONS

We found that the haplotype T-4b-Glu represents a protective haplotype against TD after long-term antipsychotic treatment. This finding suggests that human NOS3 gene may be involved in the pathogenesis of TD.