In this instance, a significant decrease in α-synuclein was detected in the saliva of 60 PD subjects (5.08 ± 3.01 pg/mL) compared to 40 healthy participants (31.3 ± 22.4 pg/mL), while the level of oligomeric α-synuclein was found to be significantly increased in PD patients (1.062 ± 0.266 ng/mL) compared, again, to the control group (0.498 ± 0.203 ng/mL). This evidence concerns the gene SNCA and Parkinson disease.