GDNF and major depressive disorder: In a study investigating the relationship between anxiety symptoms and NGF gene, NGF C/C (Cytosine/Cytosine) genotype was found in women with high anxiety and men with low anxiety.13 It has been reported that this difference in females is related to reproductive hormones, estrogen has an effect on sympathetic system dependent on NGF and progesterone shows an anxiolytic effect, which is the contrasting effect of estrogen.14 In two studies with depression and OCD, it was shown that the GDNF level was not affected by gender.