 Mixed results were found for brain-derived neurotrophic factor (BDNF) Val66Met polymorphisms.Polymorphisms in the tryptophan hydroxylase gene was found to be tentatively associated with suicidal behavior.A meta analysis of 182 case controlled genetic studies published in 2008 found Apolipoprotein E verepsilon 2 to be protective, and GNB3 825T, MTHFR 677T, SLC6A4 44bp insertion or deletions, and SLC6A3 40 bpVNTR 9/10 genotype to confer risk.