SMUG1 and major depressive disorder: Regarding the effect of combined genotypes, it was found that the T/T-A/A-G/C (DUT (rs4775748), SMUG1 c.-31A>G (rs3087404) and UNG (rs34259) carriers had an increased risk of depression, whereas the T/G-A/G-G/G carriers had a reduced risk (Table 3).