When comparing asymptomatic mutation carriers to carriers of the same mutation at the PD stage, we found a decrease in posterior and anterior basal forebrain volume in PD-GBA1 compared to asymptomatic GBA1 carriers whereas for LRRK2 we found evidence for no difference between asymptomatic mutation carriers and mutation carriers with PD (Table 2). This evidence concerns the gene LRRK2 and Parkinson disease.