Compared to the result of the 3 individual plasma biomarkers (Aβ40, α-synuclein and T-tau) used to discriminate PD patients with cognitive impairment versus controls in the study of Chen et al. [4] with sensitivity in the nineties and specificity in the seventies, our parsimonious M2 model (α-synuclein/Aβ40 and anti-α-synuclein) performed just as well (Table 5). The gene discussed is MAPT; the disease is Parkinson disease.