Parkinson’s disease (PD) is the 2nd most common neurodegenerative disorder in the world, characterized by both motor as well as many non-motor features. There are many symptomatic treatments available, that may shift significantly during the course of the disease. The biggest medical need in PD management however is treatments that actively targets disease pathology, thus being able to slow or stop the disease progression. When such therapies become available, another obstacle to administer them as early as possible in the disease progress is the fact that PD diagnosis is based on motor symptoms, that does not appear until late in the neurodegenerative process. Thus, the notion of prodromal PD has gained increased research attention in the search for earlier signs and biomarkers specific for PD. The most important genetic risk marker for PD development is mutations in the GBA1 (Glucocerebrosidase 1) gene. The gene codes for a lysosomal enzyme called Glucocerebrosidase, that normally degrades Glucocerebroside - a glucolipid mainly found in cellular membranes. When the GBA1 gene is altered, the enzyme becomes defective, and Glucocerebroside is pathologically accumulated within cells. In its biallelic state, GBA1 mutations gives rise to Gaucher disease (GD), a systemic disease mainly characterized by visceral, hematological and skeletal manifestations, but in rare cases also shows severe neurological signs and symptoms. There is a particular high endemic incidence of neuronopathic GD in the northern parts of Sweden with a distinct phenotype called “the Norrbottnian GD variant”. The GBA1-PD connection has therapeutic implications, since disease modifying treatments targeting the lysosomal pathway may be a way to find diseasemodifying treatments for PD. Since GBA1 mutations, and subsequent lysosomal dysfunction, most likely are linked to PD pathology, an overall aim of this thesis is to investigate different aspects of this gene in relation to the Swedish PD population. In Study I and II we screened the most common ...