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Science News

Blood Test May Predict Cognitive Decline in Parkinsonís

In an innovative preliminary study, researchers found that people with Parkinson’s disease (PD) who had low blood levels of an easily measured substance called epidermal growth factor (EGF) were at higher risk of developing dementia.  Along with uric acid levels, another easily measured substance, this would be a non-genetic blood test that could possibly predict the progression of a Parkinson’s symptom.  The report appears in the November 29 online edition of Annals of Neurology.

Parkinson’s disease progression differs for each person, as does cognitive functioning.  While some people may never develop cognitive impairment, others (especially in older age) will develop dementia.

The new study was carried out by Alice S. Chen-Plotkin M.D., and colleagues in the lab of John Q. Trojanowski, M.D., Ph.D., at the University of Pennsylvania School of Medicine.  The researchers drew blood from 70 study participants with PD and evaluated the participants’ cognitive ability using a standard test for dementia.  Blood was drawn again, and the cognitive test repeated, about 21 months later.

The scientists measured levels of 102 proteins in the blood samples.  Then they used statistical methods to identify biomarkers of cognitive impairment — proteins in the blood whose levels correlated with low cognitive performance at baseline or with cognitive decline at the end of the study.  After identifying a candidate biomarker, the scientists repeated the test with a second group of 113 people with PD from the same center.

 

Results

Among the first group of 70 people with PD, the researchers discovered that the levels of 11 blood proteins correlated with low cognitive test scores at the beginning of the study; of these, epidermal growth factor (EGF) had the strongest association.

  • 50 percent of those with the lowest initial levels of EGF developed dementia after 21 months.
  • The Low-EGF group were eight times more likely than the other participants to develop dementia.
  • Among the second group of 113 people with PD, the correlation between blood levels of EGF and cognitive decline was weaker.
  • Medications that the participants were taking, including levodopa and dopamine agonists, did not affect the association between EGF levels and cognitive test scores.

What Does it Mean?

The progression of PD symptoms is different for each individuals.  While there are a few clinical clues to which people with PD would develop a milder condition (for example, people with tremor dominant PD), it is very hard to predict which people with PD will develop cognitive impairment. The key finding of this study that EGF levels may help predict who would develop impairment - if replicated on larger samples - would be very helpful.  A blood test for EGF could be used as an initial screen to help predict a person’s risk of cognitive decline and thus help people with PD to plan for the future.  Currently, the EGF blood test is not available for clinical use. 

Also, EGF levels may be used to help researchers select participants for clinical trials for therapies that slow or prevent cognitive decline.  The effectiveness of potential drugs could be measured more efficiently if they could be tested on people who are at high risk of dementia.  The new study also suggests that the EGF protein may provide a clue to a molecular pathway leading to dementia in PD.

Reference: Chen-Plotkin et al. Plasma epidermal growth factor levels predict cognitive decline in Parkinson disease. Ann Neurol. (2010) pp. n/a-n/a. (http://onlinelibrary.wiley.com/doi/10.1002/ana.22271/full).

Source Date: Dec 08 2010