Glucocerebrosidase-associated Parkinson disease: Pathogenic mechanisms and potential drug treatments

Dysfunction of the endolysosomal system is implicated in the pathogenesis of both sporadic and familial Parkinson disease (PD). Variants in genes encoding lysosomal proteins have been estimated to be associated with more than half of PD cases. The most common genetic risk factor for PD are variants in the GBA gene, encoding the lysosomal enzyme glucocerebrosidase (GCase), which is involved in sphingolipid metabolism. In this review we will describe the clinical symptoms and pathology of GBA-PD, and how this might be affected by the type of GBA variant. The putative mechanisms by which GCase deficiency in neurons and glia might contribute to PD pathogenesis will then be discussed, with particular emphasis on the accumulation of α-synuclein aggregates and the spread of pathogenic α-synuclein species between the cell types. The dysregulation of not only sphingolipids, but also phospholipids and cholesterol in the misfolding of α-synuclein is reviewed, as are neuroinflammation and the interaction of GCase with LRRK2 protein, another important contributor to PD pathogenesis. Study of both non-manifesting GBA carriers and GBA-PD cohorts provides an opportunity to identify robust biomarkers for PD progression as well as clinical trials for potential treatments. The final part of this review will describe preclinical studies and clinical trials for increasing GCase activity or reducing toxic substrate accumulation