Stefani et al. (2021) assessed α-synuclein RT-QuIC of nasal brushings as a test for prodromal α-synucleinopathy and reported a sensitivity of 44.4% for iRBD, unfavourable when compared to CSF studies (Iranzo et al., 2021) but also reported a sensitivity of 46.3% for Parkinson’s disease (Stefani et al., 2021), which is lower than reported in previous studies on nasal brushings (De Luca et al., 2019; Bargar et al., 2021a), although specificity was high (89.8%). This evidence concerns the gene SNCA and Parkinson disease.