GDNF and Cognitive impairment: A negative correlation was noted between the levels of IL‐1 α, IL‐2, and GDNF and the HAM‐A score (p < .04; p < .00; p < .04).The scores of the concentrations of TNF‐α and IL‐2, IL‐8, and GDNF correlated positively with cognitive impairment (p < .00, p < .00, p < .00, p < .01), and the level of CRP correlated negatively with cognitive impairment (p < .00).