title: Exploring design-related bias in clinical studies on receptor genetic polymorphism of hypertension.
abstract: OBJECTIVE
  Although several candidate genes of Renin-Angiotensin-Aldosterone System (RAAS) have been investigated, the gene-drug relationship remains unclear. The objective was to appraise the elements of research methodology and explore potential biases, which may be contributing to discordant results in the gene-drug interaction assessment for RAAS.
  
  
  METHODS
  Systematic review of studies involving candidate polymorphisms, searching PubMed, and EMBASE.
  
  
  RESULTS
  Sixteen studies were identified. Nine studies had a genomic evaluation as the primary question. Six studies investigated more than one gene. A gene-drug interaction was evaluated in two studies and only one of the studies had a placebo arm for accurately exploring the interaction. Almost, 90% of the studies had sample sizes of less than 500 patients. Four studies combined the allele frequencies of the heterozygotes group with one of the homozygotes groups. Almost one quarter of the studies combined different therapeutics in one group. Five studies included patients in one group from previous studies in which selection criteria were not quite similar.
  
  
  CONCLUSIONS
  Most studies contain several methodological limitations. Also biases driven from patient selection, combining different alleles, combining different therapeutics, and combining end points may have occurred in these studies. These limitations and biases may contribute to inconsistency of the results of these studies.
authors.affiliation: Centre for Evaluation of Medicines (CEM), St Joseph's Hospital, McMaster University, Level P1, Hamilton, Ontario, Canada. farahap@mcmaster.ca
authors.forename: Pendar
authors.initials: P
authors.lastname: Farahani
authors.forename: Lisa
authors.initials: L
authors.lastname: Dolovich
authors.forename: Mitchell
authors.initials: M
authors.lastname: Levine
mesh_terms: D047228:Angiotensin II Type 1 Receptor Blockers / Q000627:therapeutic use; D000806:Angiotensin-Converting Enzyme Inhibitors / Q000627:therapeutic use; D000959:Antihypertensive Agents / Q000627:therapeutic use; D015982:Bias; D020022:Genetic Predisposition to Disease; D006801:Humans; D006973:Hypertension / Q000188:drug therapy / Q000235:genetics*; D010597:Pharmacogenetics; D011110:Polymorphism, Genetic; D012084:Renin-Angiotensin System / Q000235:genetics; D012107:Research Design
chemical_list: D047228:Angiotensin II Type 1 Receptor Blockers; D000806:Angiotensin-Converting Enzyme Inhibitors; D000959:Antihypertensive Agents