In addition, the reductions in Grn mRNA and PGRN protein in PD may be further compounded by sequestration of PGRN into aggregates or inclusions evident in the PD SNpc in a manner analogous to what has been reported for other endo-lysosomal membrane proteins (LAMP1 and Rab5) accumulating at amyloid plaques (60). Here, RAB5A is linked to Parkinson disease.