α-syn and SNP rs356219 as a potential biomarker in blood for Parkinson's disease in Mexican Mestizos

Clinical criteria diagnose Parkinson's disease (PD), therefore, it is crucial to find biological elements that could support diagnosis or even act as prognostic tools of PD. The SNCA gene codifies a protein called α - synuclein; several studies associate genetic and biochemical factors of SNCA with PD, including transcript and plasmatic protein levels, however, contradictory evidence indicates inconclusive results. We aim to compare SNCA mRNA expression, plasmatic α-syn protein and rs356219 SNP between PD cases and a control group, and to identify a potential biomarker in Mexican mestizos', focusing on these three components determined in blood. We included 88 PD patients and 88 age-matched controls. We observed higher α-syn protein and decreased SNCA mRNA levels in PD subjects, compared to control group (p = 0.044 and p 0.001, respectively). A statistically significant difference was found in allelic and genotypic frequencies of SNP rs356219 between PD patients and normal subjects (p = 0.006 and p = 0.023, respectively). Logistic regression analysis determined as optimal predictors of PD the GG genotype of SNP rs356219 (OR 2.49; p = 0.006) in a recessive model and α-syn protein (OR 1.057; p = 0.033). Furthermore, the G allele of SNP rs356219 was associated with higher plasmatic α-syn and mRNA levels in PD subjects. The receiver operating curves (ROC) distinguished PD from healthy controls with good sensitivity and specificity considering the plasmatic α-syn protein (AUC = 0.693, Sensitivity = 66.7 %, Specificity = 63.9 %) or a predictive probability of plasmatic α-syn protein and SNP rs356219 in a single model (AUC = 0.692, Sensitivity = 62.3 %, Specificity = 62.5 %). The performance of this classifier model in PD at early stage (n = 31) increase the discriminant power in both, plasmatic α-syn protein (AUC = 0.779, Sensitivity = 72.7 %, Specificity = 73.9 %) and predictive probability (AUC = 0.707, Sensitivity = 63.6 %, Specificity = 62.5 %). We propose that α-syn protein and SNP rs356219 together may work as a good signature of PD, and they can be suggested as a non-invasive biomarker of PD risk.