NPPA and vitamin B deficiency: In examining whether B-vitamin deficiency links proinflammatory responses and KP activation in PD, it was found that plasma flavin mononucleotide (FMN, P < 0.001), PLP (P < 0.001), pyridoxal (P < 0.001) and 4-pyridoxic acid (4-PA, P < 0.001) were all lower in PD participants when compared to controls (Fig. 2b and Supplementary Fig. 4a).