Vivacqua et al. showed that the content of α-synuclein oligomers in the saliva of PD (Parkinson’s disease) patients is significantly positively correlated with its concentration in CSF, and that PD-MCI (Parkinson’s disease with mild cognitive impairment) patients have higher salivary oligomer levels than PD patients without cognitive impairment (42). This evidence concerns the gene SNCA and Parkinson disease.