PTGS2 and major depressive disorder: Su et al (2014) found that the ‘at risk' A allele and the A/G genotype in the COX2 rs4648308 polymorphism significantly increased the risk of developing IFN-α-induced depression. In addition, the ‘at risk' A/G genotype was associated with lower DHA levels before and during IFN-α treatment (Su et al, 2010).