HLA-DRA and Parkinson disease: Moreover, we evaluated respective NAb titres in association with different single nucleotide polymorphisms (SNPs) of genes which either have been reported to influence the activity of the adaptive immune system, the amyloid cascade or have been associated with the occurrence of PD (APOE[17], [18], GSK3B[19], [20], HLA-DRA[21], [22], HSPA5[23], [24], SNCA[25]–[27], and STK39[28], [29]).