Biological fluid levels of iron and iron‐related proteins in Parkinson’s disease: Review and meta‐analysis

Abstract Background and purpose Several studies suggested a role or iron in the pathogenesis or Parkinson's disease (PD), and substantia nigra iron concentrarions have been found increased in PD. However, the results on cerebrospinal (CSF) and serum/plasma iron levels in PD patients have been controversial. The aim of this systematic review and meta‐analysis was to establish the CSF and serum/plasma levels of iron and iron‐related proteins (ferritin, transferrin, lactoferrin, haptoglobin, and hepcidine) levels, and the urine levels of iron, in patients with PD. Methods Four databases (PubMed, EMBASE, MedLine, and Web of Science – Core Collection) were reviewed for studies published from 1966 to October 5, 2020. References of interest were identified. A meta‐analysis of eligible studies was performed according to the Preferred Reporting Items for Systematic Reviews and Meta‐analyses (PRISMA) and Meta‐analysis of Observational Studies in Epidemiology (MOOSE) guidelines, using the R software package meta . Results A non‐significant trend towards higher CSF iron levels and marginally significantly lower serum/plasma iron levels was observed in patients with PD compared with age‐ and sex‐matched controls. CSF and serum/plasma ferritin and transferrin concentrations, and serum/plasma lactoferrin and haptoglobin concentrations did not differ significantly between PD patients and controls. Conclusion The findings of this study suggest an association between decreased serum/plasma iron levels and, possibly, higher CSF iron levels with risk of PD.