In vitro autoradiography studies revealed that [3H]HY-2-15 specifically binds to α-syn in MSA (Kd = 4.5 nM) and PD (Kd = 5.1 nM) postmortem tissues, although residual binding to tauopathies (CBD: 18 nM; PSP: 7.1 nM) suggested potential tau aggregate interactions. Here, MAPT is linked to Parkinson disease.