SLC6A3 and Parkinson disease: In Parkinson disease, increased leucocytes correlated with higher UPDRS III scores (rs = 0.19, P = 0.027), lower DAT activity in the caudate (rs = −0.20, P = 0.025), poorer cognitive performance in psychomotor speed, language, episodic memory and executive function (rs between −0.25 and −0.44, P < 0.01), and higher NfL in CSF, but all factors, except performance in language and executive function, were unrelated with leucocytes after age adjustment.