We did not observe any interactions between APOE E4 dosage and carrier status, suggesting that APOE E4 dosage contributes an additive risk (on the log odds scale) to cognitive/memory/psychotic symptoms in LRRK2 p.G2019S and GBA1 p.N409S carriers with PD; however, we were underpowered to fully test this hypothesis (see Table S19 for sample sizes). This evidence concerns the gene GBA1 and Parkinson disease.