The demonstration of abnormal expression of lysosomal markers in PD brain in areas mapping to neuronal degeneration and LB deposition highlights the importance of this pathway.28 The most common GD allele found in sporadic PD is N370S.4 This mutation causes protein misfolding and has the highest residual GCase activity of any GBA mutation.4 This suggests protein misfolding and endoplasmic reticulum stress may contribute to PD risk in heterozygotes. The gene discussed is GBA1; the disease is Parkinson disease.