Additional information has already been published . Participants with different LRRK2 variants were included in this study. In the PD+/LRRK2+ group, seven participants carried the p.G2019S variant, two had the p.N1437S variant, and one each had the p.R1441H and p.I2020T variants. In the PD-/LRRK2+ group, six individuals carried the p.G2019S variant, while one each had the p.R1441C and p.S901L variants. Importantly, carriers of pathogenic and likely pathogenic variants in 68 PD-linked genes were excluded in the iPD and control groups, as specified in the ROPAD protocol , . A total of forty-one dust samples were collected from vacuum cleaner bags provided by the participants and stored at room temperature until analysis. In addition, twenty-four matched serum samples were collected (Table ) and stored at -80 °C until the analysis. Figure shows the number of samples per group, and the analyses performed (described further in the following sections).