Parkinson’s Disease (PD) is a common neurodegenerative disorder that impairs voluntary movement in 1%-2% of the population by age 65. In Canada, 100,000 affected individuals currently require long-term care, and our growing elderly population presents an increasing challenge to caregivers and scarce healthcare resources.
Parkinson’s Disease is named after James Parkinson who first characterized it in England in 1817.
Pathological & Clinical Manifestations
Current therapies for PD are purely symptomatic and do not alter either disease progression or the underlying neuropathology that includes intraneuronal deposits of insoluble proteins known as Lewy bodies and loss of pigmented neurons in the substantia nigra. These neurons normally project processes to the striatum where they produce and secrete the neurotransmitter dopamine.
Progressive loss of these dopaminergic neurons in PD reduces the capacity of the remaining nerve endings in the striatum to synthesize dopamine in sufficient quantities. The resulting dopamine deficit alters the normal neural circuitry in a region of the brain called the basal ganglia, which is important for initiating voluntary movement, and gives rise to the clinically recognized motor symptoms of PD which include muscle rigidity, bradykinesia, resting tremor, and difficulty in maintaining upright posture.
Other brain areas (cortical, subcortical, brainstem) where dopamine is not the primary neurotransmitter are also affected by Lewy body pathology indicating that PD pathology, is more widespread and not specific to dopamine-producing neurons. This multisystem degeneration likely underlies the psychiatric disturbances prevalent in PD patients. For example, depression and dementia affect ~50% of PD patients, and the rate of cognitive decline in PD dementia is comparable to that in Alzheimer's disease.
The majority of PD cases are considered sporadic, where there is little or no verifiable family history of the disorder, underlying the complex and heterogeneous etiology of the disorder. However, in a small number of cases, familial PD has been identified as an inheritable trait. Genetic analyses of these PD families have revealed several genes with strong linkage to PD as a result of mutations. Scientists at the Tanz CRND and in many laboratories around the world are working to understand how the proteins encoded by these genes might fit into one or more biochemical cascades that can be manipulated in PD patients by pharmacological or genetic therapies in order to prevent or halt the degeneration at an early stage.
Parkinson's Disease Breakthroughs
Scientists at the Tanz Centre have contributed to the understanding of Parkinson’s disease through several breakthroughs, including:
Identifying the protective role of PINK1 protein to suppress neuronal death and loss-of-function effects induced by PD-linked mutations (2004).
Characterizing regulation of α-synuclein solubility in neurons by specific brain proteins, a process that is disrupted by PD-linked mutations in α-synuclein (2006). Identification of these factors has implications for understanding PD pathogenesis.
Discovering that Corticobasal Degeneration can be caused by mutations in the progranulin gene (2006).
Identifying several extended families with mutations in the Parkin, DJ-1, PINK1, LRRK2 and GBA genes (2000-2006).
Discovering that the Parkinson's disease-linked A30P mutant form of α-Synuclein displays defective membrane binding, a feature that was not observed for the naturally occurring murine protein (which has an A53T substitution like the human PD-causing mutant form of α-synuclein) and human wild-type proteins. These findings suggest that the various Parkinson’s disease-causing mutants may have different physiological consequences in vivo and could possibly contribute to early onset Parkinson's disease via unique mechanisms (2000, 2002).