FADS2 and major depressive disorder: The ratio 22:5n-3/20:5n-3, reflecting elongase (Elovl5) activity, was higher in MDD, as was the ratio 20:3n-6/20:2n-6, which reflects Δ8-desaturase activity (Fads2), whereas the ratio 22:6n-3/22:5n-3, which reflects Δ-6 desaturase activity but also includes elongase (Elovl2) and β-oxidation steps, was lower (see Figure 1, Table S2 in Supplementary Material).