CX3CL1 and Parkinson disease: The CSF levels of transforming growth factor β1 and 2 (TGFβ1 and TGFβ2) [32] and ratios between amyloid-β (Aβ) 42 with fractalkine/CX3CL1 [33], as well as levels of complement factors C3 and fH [34], are all altered in PD.