GDNF and Parkinson disease: Chauhan et al. (2001) reported a significant reduction of GDNF in the SNpc of patients with PD, which was up to eight times greater than the reduction of other NTFs, thus suggesting that GDNF may be considered as the most vulnerable and earliest NTF to decrease in SNpc neurons that survived to neurodegeneration. Conflicting reports are also available; a lack of difference between healthy subjects and patients with PD, for instance, was documented in a post-mortem study (Mogi et al., 2001).