GBA1 and Parkinson disease: ,16 Previous studies have shown that pathogenic LRRK2 gain-of-function variants are associated with slower PD progression, while GBA loss-of-function variants are associated with faster PD progression.17, 18, 19, 20 Interestingly, a study by PPMI reported significantly lower rates of α-syn SAA positivity in carriers of the LRRK2 G2019S variant than those with sporadic PD.21