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

The treatment of seriously mentally ill patients is complicated by variability in individual response to psychotropic drugs. Some patients remain treatment refractory even after two to three therapeutic modalities. Other patients experience adverse events that range from mild discomfort, to poor compliance, to life threatening. Genaissance Pharmaceuticals is actively engaged in a candidate gene-based haplotype (HAP Marker) approach to the pharmacogenetics of drug response and adverse events. In the present article, we review reasons why HAP Markers are more useful than single nucleotide polymorphisms (SNPs) for discovering genetic correlations to clinical response. In addition, we review our approach to HAP Marker discovery, which involves discovering SNPs in the functional regions of genes by sequencing, organizing these SNPs into HAP Markers for an index population of ethnically diverse individuals and calculating population frequencies for these HAP Markers. For clinical correlations, HAP Markers are defined and correlated to clinical data using the in-house DecoGen Informatics System. This approach has clear implications for the discovery of psychiatric disease-associated genes as well as for the development of safer, more efficacious psychiatric drugs.

Clozapine blunts N-methyl-D-aspartate antagonist-induced psychosis: a study with ketamine

Several lines of evidence suggest that the glutamatergic N-methyl-D-aspartate (NMDA) receptor is involved in the antipsychotic efficacy of the atypical antipsychotic agent clozapine. Clinical data on the interaction between clozapine's mechanism of action and NMDA receptor function have been lacking secondary to a paucity of pharmacologic probes of the NMDA system. We have utilized a double-blind, placebo-controlled infusion paradigm with subanesthetic doses of the NMDA antagonist ketamine to test the hypothesis that clozapine would blunt ketamine-induced psychotic symptoms in schizophrenic patients. Ten schizophrenic patients underwent ketamine infusions while antipsychotic drug free and also during treatment with clozapine. Antipsychotic drug-free patients experienced increases in ratings of positive and negative symptoms. Clozapine treatment significantly blunted the ketamine-induced increase in positive symptoms. These data suggest that NMDA receptor function may be involved in the unique antipsychotic efficacy of clozapine.

New dimensions in the pharmacologic treatment of schizophrenia and related psychoses

During the past 5 years unprecedented advances have taken place in the psychopharmacology of schizophrenia and related psychoses. Clozapine and risperidone, two prototypic novel antipsychotic drugs, have had a significant impact on the treatment of psychotic disorders. Additionally, they have ushered in another generation of antipsychotic drugs with complex pharmacologic profiles, potentially enhanced efficacy, and more benign side-effect profiles than previously associated with conventional antipsychotic medications. This review highlights these developments, implications for the management of psychotic disorders, and the use of novel antipsychotic drugs in specific clinical subgroups.