Parkinson's Disease - Introduction

NMDA Receptors. Also of interest in PD are processes that occur in an area of the brain called the subthalamic nucleus. Here, receptors known as glutamatergic N-methyl-D-aspartate (NMDA) become persistently overexcited and produce high levels of calcium ions within brain cells. This in turn leads to a cascade of events that trigger oxygen-free radicals and cell damage.

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Immune Factors and the Inflammatory Response. An over-responsive immune system triggered by initial damage may also play a role in perpetuating Parkinson's disease. When the immune system becomes overactive, it produces excessive numbers of potent factors called cytokines, which cause inflammation and further injury in brain cells. Important cytokines under investigation are interleukin-1 and tumor necrosis factor.

Genetic Factors

Specific genetic factors appear to play a strong role in early-onset Parkinson's disease, an uncommon form of the disease. Research from the last several years suggests that multiple genetic factors may also be involved in late-onset Parkinson?s disease. Several important studies, published in 2005, lay the groundwork for potential genetic screening for this disease. Researchers identified the leukine-rich repeat kinase 2 (LRRK2) gene, located on a region of chromosome 12 known as PARK8, as a key gene involved in inherited forms of Parkinson?s. The researchers estimate that a single gene mutation in LRRK2 may be responsible for 5% of inherited Parkinson?s cases and approximately 2% of isolated cases.

Early Onset PD. The cases of genetic early-onset Parkinson's disease have most often been detected in specific family groups.

Defective genes that regulate the molecules alpha synuclein and parkin, which are important in the PD disease process, may be responsible for a number of early-onset cases. For example, genetic abnormalities the alpha synuclein protein have been detected in some early-onset Parkinson's patients of European descent.
The parkin gene may be the cause of many cases of early-onset Parkinson's in young adults. (Parkinson's cases associated with this mutation tend to progress slowly and respond well to treatment, even after years of symptoms. Dementia is also rare with this form.)

Late Onset PD. Two landmark studies published in the Journal of the American Medical Association provided the first evidence of a genetic link to late-onset Parkinson?s disease. In these 2001 studies, researchers found that regions on chromosomes 5, 6, 8, 9, and 17 were implicated with Parkinson?s. The parkin gene (located on chromosome 6) and the tau gene (located on chromosome 17) were both found in families that had late onset Parkinson?s. Parkin was previously thought to be responsible only for early-onset Parkinson?s, but this research identified it in families that had both early- and late-onset disease forms. These studies also bolstered the theory that Parkinson?s does have a genetic component and is not caused solely by environmental factors. A 2005 study found that a G2019S mutation in the LRRK gene, located on the PARK8 region of chromosome 12, was definitively associated with late-onset Parkinson?s disease in North American and European families .