title: Reduced hippocampal volumes in healthy carriers of brain-derived neurotrophic factor Val66Met polymorphism: meta-analysis.
abstract: OBJECTIVE
  Converging evidence suggests that the brain-derived neurotrophic factor (BDNF) gene Val66Met polymorphism affects brain structure. Yet the majority of studies have shown no effect of this polymorphism on hippocampal volumes, perhaps due to small effect size.
  
  
  METHODS
  We performed a meta-analysis of studies investigating the association between Val66Met BDNF polymorphism and hippocampal volumes in healthy subjects by combining standardized differences between means (SDM) from individual studies using random effect models.
  
  
  RESULTS
  Data from 399 healthy subjects (255 Val-BDNF homozygotes and 144 carriers of at least one Met-BDNF allele) in seven studies were meta-analysed. Both the left and right hippocampi were significantly larger in Val-BDNF homozygotes than in carriers of at least one Met-BDNF allele (SDM = 0.41, 95% Confidence Interval = 0.20; 0.62, z = 3.86, P = 0.0001; SDM = 0.41; 95% Confidence Interval = 0.20; 0.61, z = 3.81, P = 0.0001, respectively), with no evidence of publication bias.
  
  
  CONCLUSIONS
  Healthy carriers of BDNF gene Val66Met polymorphism show bilateral hippocampal volume reduction. The effect size was small, but the same direction of effect was seen in all meta-analyzed studies. The association with the BDNF gene Val66Met polymorphism makes hippocampal volume a potential candidate for an endophenotype of disorders presenting with reduced hippocampal volumes.
authors: Department of Psychiatry, Dalhousie University, Halifax, Canada. tomas.hajek@dal.ca
authors: Tomas
authors: T
authors: Hajek
authors: Miloslav
authors: M
authors: Kopecek
authors: Cyril
authors: C
authors: Höschl
mesh_terms: D019208:Brain-Derived Neurotrophic Factor / Q000235:genetics*; D058068:Endophenotypes; D005838:Genotype; D006579:Heterozygote; D006624:Hippocampus / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D020125:Mutation, Missense; D009929:Organ Size; D020641:Polymorphism, Single Nucleotide
chemical_list: D019208:Brain-Derived Neurotrophic Factor