COMT and major depressive disorder: For example, two published studies on the role of the COMT val158met polymorphism in antidepressant treatment response investigating samples of 102 and 346 patients, respectively, report a tentative negative effect of the COMT 158Met/Met genotype on mirtazapine and citalopram response in MDD (Arias et al., 2006; Szegedi et al., 2005).