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Similarities Between Genetic and Non-Genetic PD May Aid Research

People with the most common genetic form of Parkinson’s disease (PD) experience symptoms similar to those associated with non-genetic PD. This suggests that we may be able to study genetic models as a research window on Parkinson’s as a whole. The study appeared in the October 15 online issue of the journal Movement Disorders. Only a small portion of cases of Parkinson’s are caused strictly by genetics. But among those cases, the gene known as LRRK2, is especially common. Among people with PD who are of Eastern European Jewish descent, about 15-18 percent carry a LRRK2 mutation known as G2019S. The mutation was the focus of a consortium of researchers in New York, NY, and Tel Aviv, Israel, led by Roy N. Alcalay, M.D., M.S., of the PDF Research Center at the Columbia University Medical Center. Dr. Alcalay and colleagues recruited 488 participants who had PD and had at least two Ashkenazi Jewish grandparents and screened them for LRRK2 G2019S mutations. Using standard tests, rating scales and questionnaires, they put together a picture of each participant’s experience with Parkinson’s.

Results

  • Of the 488 participants, 20 percent carried the LRRK2 G2019S mutation.
  • Overall, carriers of the gene mutation reported a similar experience with Parkinson's as non-carriers.
  • There were some differences between the two groups — for example, carriers of the gene mutation were more likely to be women, were more likely to have symptoms in their legs and affecting their gait, but were less likely to experience tremor.
  • Carriers who experienced balance problems did not experience cognitive impairment, yet non-carriers frequently experienced the two symptoms together.

What Does It Mean?  

The symptoms of Parkinson’s, and the way in which the disease develops, can vary greatly from one person to another, making it difficult for doctors to make an accurate prognosis. Researchers have looked to genes to explore whether one’s genetic background may explain how the disease progresses. This study found that people who develop Parkinson’s because of one relatively common gene mutation experience the disease in very much the same way as do people with non-genetic Parkinson’s, with a few exceptions. This similarity between the two groups is very encouraging for research, because it suggests that researchers can now use a genetic model of LRRK2 as a way to better understand all forms (both genetic and non-genetic) of Parkinson’s.

Time Course of Neuron Loss in Parkinson’s Disease

For the first time, researchers have estimated in detail the pace at which certain brain cells are lost to Parkinson’s disease (PD) during its progression. They report their results in the August 2013 issue of Brain. Parkinson’s disease results from the gradual loss of brain cells that produce dopamine. To understand these changes, researchers led by Jeffrey Kordower, Ph.D., at the PDF Research Center at Rush University Medical Center studied how certain areas of the brain change after diagnosis. They examined brain tissue taken from 28 people who died between one and 27 years after a Parkinson’s diagnosis, then compared this tissue to the tissue derived from the brains of elderly people who did not have the disease. The tissue sections were taken from two areas of the brain: the substantia nigra (SNc), where dopamine neurons live, and the putamen, where these neurons release their dopamine.

Results

  • Brain tissue from people in the study who had died soonest after a Parkinson’s diagnosis (one to seven years) had 50 – 90 percent fewer healthy dopamine neurons in the SNc than did the brain tissue from people who did not have Parkinson’s.
  • Brain tissue from people who died after many years of living with PD showed only slightly greater neuron loss than people who died soon after diagnosis.
  • When researchers examined the brain of one person who died within one year from diagnosis, the SNc showed a loss of only 10 percent of a specific type of neuron that contains melanin.

What Does It Mean?  

A key finding of this study is that people with Parkinson’s lost most of their healthy dopamine-producing neurons within just four years of diagnosis. This suggests the importance of diagnosing Parkinson’s early in its progression and finding treatments that will slow, stop or reverse Parkinson’s in its early stages. At the same time, the study found that most people with Parkinson’s seemed to lose another type of neuron, one that contains melanin, at a slower and more variable pace. This finding provides hope that there are remaining dopamine-producing neurons which could potentially be restored or made healthy with treatment.

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