Serum uric acid and total bilirubin as putative biomarkers of resistance in Prodromal Parkinson's disease: Longitudinal data from the PPMI study.

BackgroundThe role of blood uric acid and more recently bilirubin as biomarkers in symptomatic motor PD has been increasingly established in the literature. ObjectiveOur present study assessed the role of serum uric acid and total bilirubin as putative biomarkers in a prodromal PD cohort followed longitudinally. MethodsLongitudinal 5-year serum uric acid and total bilirubin measurement data of 65 Prodromal PD patients (including REM Sleep Behavior disorder (RBD), N=39 and Hyposmia, N=26) with an abnormal DATSCAN imaging were downloaded from the Parkinsons Progression Markers Initiative (PPMI) database. This cohort was compared with 423 de novo sporadic PD patients and 196 healthy controls enrolled in the same study. ResultsAfter adjusting for age, sex and Body Mass Index (BMI), baseline and 5-year longitudinal serum uric acid levels were higher in the Prodromal cohort and RBD subgroup as compared to the motor PD cohort. This was also true for longitudinal measurements in the Hyposmic subgroup. In contrast, baseline and longitudinal serum total bilirubin did not differ between each prodromal group and the PD cohort. ConclusionsOur results are indicative of a role of serum uric acid (but probably not of total bilirubin) as a marker of neuroprotection, in a certain subgroup of premotor patients exhibiting exclusively non motor features (hyposmia or RBD). It is possible that an inherent antioxidant resistance of a subset of RBD or hyposmia patients with high serum uric acid level delayed or precluded the emergence of a motor PD phenotype as opposed to the PD cohort.