GBA1 and Parkinson disease: To investigate potential gene dosing effects of GBA1 D409V KI and because PD patients with mutations in the GBA1 gene tend to be heterozygous, we also examined GCase activity and GSL levels in mice heterozygous for the GBA1 D409V KI mutation compared to WT mice, using the same methodology deployed at Amicus for analyses of hom GBA1 D409V KI mice.