In the PD patients, we found that plasma CRP and SAA were associated with the CSF KYN/TRP ratio (R = 0.57, P = 0.007; Fig. 5A; and R = 0.52, P = 0.016; respectively), suggesting a potential connection between peripheral inflammation and central tryptophan metabolism in PD subjects. The gene discussed is CRP; the disease is Parkinson disease.