title: Association study of 12 polymorphisms spanning the dopamine D(2) receptor gene and clozapine treatment response in two treatment refractory/intolerant populations.
abstract: BACKGROUND
  Dopamine D(2) receptor blockade is the major basis for the antipsychotic action of typical antipsychotic drugs (AP) and a necessary but not sufficient basis for the antipsychotic action of atypical APs such as clozapine and other multireceptor antagonists which rely, in part, upon 5-HT(2A) antagonism. Genetic factors affecting the density and/or function of D(2) receptors may therefore affect AP response.
  
  
  OBJECTIVE
  This exploratory study investigates the effect of 12 single nucleotide polymorphisms (SNPs) spanning the entire dopamine D(2) gene on clozapine response in two distinct schizophrenic populations (Caucasian and African-American) refractory or intolerant to conventional APs.
  
  
  METHODS
  This study included 183 Caucasian and 49 African-American DSM-III-R or DSM-IV schizophrenics. Genotyping was determined by 5'-exonuclease fluorescence assays. Within each population genotype, allele, allele +/-, and haplotype frequencies were compared between responders and non-responders by X (2) tests. Linkage disequilibrium analysis was also performed.
  
  
  RESULTS
  In the Caucasian sample, no significant associations were found for individual SNP tests; however, two haplotypes were identified as having significant protective effects on treatment outcome. In the African-American sample, individual SNP tests identified the Taq1A, Taq1B, and rs1125394 markers as being predictive of clozapine response. Haplotype analyses identified four protective haplotypes containing these SNPs. In addition, no association between the -141C Ins/Del site and clozapine response was found in either population.
  
  
  CONCLUSIONS
  Interindividual variability in clozapine response among treatment refractory/intolerant patients is still not fully understood and likely involves multiple factors. This exploratory analysis suggests that the D(2) receptor gene may be one such factor.
authors.affiliation: Neurogenetics Section, Center for Addiction and Mental Health, University of Toronto, 250 College Street, Toronto, Ontario M5T 1R8, Canada.
authors.forename: Rudi
authors.initials: R
authors.lastname: Hwang
authors.forename: Takahiro
authors.initials: T
authors.lastname: Shinkai
authors.forename: Vincenzo
authors.initials: V
authors.lastname: De Luca
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Müller
authors.forename: Xingqun
authors.initials: X
authors.lastname: Ni
authors.forename: Fabio
authors.initials: F
authors.lastname: Macciardi
authors.forename: Steven
authors.initials: S
authors.lastname: Potkin
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Lieberman
authors.forename: Herbert Y
authors.initials: HY
authors.lastname: Meltzer
authors.forename: James L
authors.initials: JL
authors.lastname: Kennedy
mesh_terms: D000328:Adult; D001741:Black or African American / Q000235:genetics; D000483:Alleles; D014150:Antipsychotic Agents / Q000494:pharmacology / Q000627:therapeutic use; D003024:Clozapine / Q000494:pharmacology / Q000627:therapeutic use*; D004351:Drug Resistance / Q000235:genetics; D004361:Drug Tolerance / Q000235:genetics; D005260:Female; D005787:Gene Frequency; D005838:Genotype; D006239:Haplotypes; D006801:Humans; D015810:Linkage Disequilibrium; D008297:Male; D008875:Middle Aged; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D017448:Receptors, Dopamine D2 / Q000235:genetics*; D012559:Schizophrenia / Q000188:drug therapy* / Q000208:ethnology / Q000235:genetics; D016896:Treatment Outcome; D044465:White People / Q000235:genetics
chemical_list: D014150:Antipsychotic Agents; D017448:Receptors, Dopamine D2; D003024:Clozapine