A 2019 study published in the International Journal of Molecular Sciences looked at the interaction of mitochondria, a-synuclein and the endo-lysosomal system. PD is characterized by dopaminergic neuronal loss and the alpha-synuclein-containing Lewy body inclusions in the substantia nigra. Genetic investigations have revealed evidence of the involvement of mitochondrial function, alpha-synuclein (α-syn) aggregation, and the endo-lysosomal system, in disease pathogenesis. Although familial parkinsonism makes up less than 10% of adult parkinsonism, the findings generated from genetic studies have enhanced the understanding of the neuron degeneration processes. These include mitochondrial dysfunction, disruption of network integrity, and α-syn accumulation; the functions of the proteasome and endo-lysosomal pathways in cellular degradation. Mitochondrial dysfunctions, endo-lysosomal disruptions, and α-syn aggregation mutually interact within neurons, while α-syn prion-like propagation may also be associated with PD in an inter-neuronal manner. Both mitochondria and endo-lysosomal dysfunction contribute to the development of α-syn pathology, however, the specific organelle playing the most important role might be decided by genetic and environmental factors. Most likely, a vicious cycle may develop once one system becomes dysfunctional. Further elucidation of the precise molecular mechanisms involved in the pathogenesis of PD may lead to the development of future therapeutic targets to treat PD.