title: Meta-analyses of the 5-HTTLPR polymorphisms and post-traumatic stress disorder.
abstract: OBJECTIVE
  To conduct a meta-analysis of all published genetic association studies of 5-HTTLPR polymorphisms performed in PTSD cases.
  Potential studies were identified through PubMed/MEDLINE, EMBASE, Web of Science databases (Web of Knowledge, WoK), PsychINFO, PsychArticles and HuGeNet (Human Genome Epidemiology Network) up until December 2011.
  
  
  METHODS
  Published observational studies reporting genotype or allele frequencies of this genetic factor in PTSD cases and in non-PTSD controls were all considered eligible for inclusion in this systematic review.
  
  
  METHODS
  Two reviewers selected studies for possible inclusion and extracted data independently following a standardized protocol.
  
  
  METHODS
  A biallelic and a triallelic meta-analysis, including the total S and S' frequencies, the dominant (S+/LL and S'+/L'L') and the recessive model (SS/L+ and S'S'/L'+), was performed with a random-effect model to calculate the pooled OR and its corresponding 95% CI. Forest plots and Cochran's Q-Statistic and I(2) index were calculated to check for heterogeneity. Subgroup analyses and meta-regression were carried out to analyze potential moderators. Publication bias and quality of reporting were also analyzed.
  
  
  RESULTS
  13 studies met our inclusion criteria, providing a total sample of 1874 patients with PTSD and 7785 controls in the biallelic meta-analyses and 627 and 3524, respectively, in the triallelic. None of the meta-analyses showed evidence of an association between 5-HTTLPR and PTSD but several characteristics (exposure to the same principal stressor for PTSD cases and controls, adjustment for potential confounding variables, blind assessment, study design, type of PTSD, ethnic distribution and Total Quality Score) influenced the results in subgroup analyses and meta-regression. There was no evidence of potential publication bias.
  
  
  CONCLUSIONS
  Current evidence does not support a direct effect of 5-HTTLPR polymorphisms on PTSD. Further analyses of gene-environment interactions, epigenetic modulation and new studies with large samples and/or meta-analyses are required.
authors.affiliation: Unidad de Docencia, Investigación y Formación en Salud Mental (UDIF-SM) Subdirección General de Salud Mental y Asistencia Psiquiátrica, Servicio Murciano de Salud and CIBER de Epidemiología y Salud Pública (CIBERESP), Murcia, Spain. fernando.navarro@carm.es
authors.forename: Fernando
authors.initials: F
authors.lastname: Navarro-Mateu
authors.forename: Teresa
authors.initials: T
authors.lastname: Escámez
authors.forename: Karestan C
authors.initials: KC
authors.lastname: Koenen
authors.forename: Jordi
authors.initials: J
authors.lastname: Alonso
authors.forename: Julio
authors.initials: J
authors.lastname: Sánchez-Meca
mesh_terms: D020022:Genetic Predisposition to Disease; D006801:Humans; D011110:Polymorphism, Genetic / Q000235:genetics*; D050486:Serotonin Plasma Membrane Transport Proteins / Q000235:genetics*; D013313:Stress Disorders, Post-Traumatic / Q000235:genetics*
chemical_list: C493230:SLC6A4 protein, human; D050486:Serotonin Plasma Membrane Transport Proteins