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Science News

Test for Alzheimerís Protein Predicts Cognitive Decline in Parkinsonís

Scientists have found that a test being studied for the early diagnosis of Alzheimer’s disease also may predict whether a person with Parkinson’s disease (PD) will develop dementia.  In new research, low levels of a protein known as amyloid b 1-42 in the cerebrospinal fluid of people with PD were associated with an increased risk for dementia.  The results appear in the September 21, 2010 issue of Neurology.

Cognitive decline is one of the most disabling of PD symptoms, and up to 80 percent of people with PD develop dementia.  Certain clinical features of PD have been associated with a higher risk of dementia, including older age, being male, lack of tremor, and more balance difficulties.  Yet there is currently no biomarker — no blood test or brain imaging technique, for example — that can predict the likelihood that a person’s PD will progress with dementia.  

Autopsy findings from people with Parkinson’s disease who suffered from dementia show that the cause of dementia is usually either one of the two: either the individual’s Parkinson’s disease progressed to the cortex (the part of the brain that play a key role in memory, attention, perceptual awareness, thought, language, and consciousness), or the person developed Alzheimer’s disease.

Researchers led by Andrew Siderowf, M.D., M.S.C.E., at the University of Pennsylvania Medical Center tested whether three biomarkers associated with progression of Alzheimer’s disease also would help identify people with PD at risk of cognitive decline.  The biomarkers tested are proteins found in the cerebrospinal fluid — fluid that bathes and cushions the spine and brain.  It is extracted through a spinal tap, a needle inserted between vertebrae in the lower back. 

The researchers collected cerebrospinal fluid from 45 people with PD.  Then they measured levels of amyloid b1-42, tau, and p-tau181p protein in the fluid.  In addition, they evaluated all study participants using a standard test for cognitive decline at the time of enrollment, and once a year thereafter for up to three years. 

Results

  • At the beginning of the study, there was no association between the level of any of the biomarkers and the cognitive status of participants.
  • Study participants with the lowest cerebrospinal fluid levels of amyloid b 1-42 at the beginning of the study (below 192 pg/mL) had the most rapid cognitive decline, progressing from essentially normal cognition to PD with dementia within two years.
  • Levels of tau and p-tau181p proteins were not associated with cognitive decline.

What Does it Mean?

The study demonstrates that a biomarker in cerebrospinal fluid can provide information about the prognosis of cognitive decline in people with PD.  However, the number of study participants was small and the researchers followed them for a relatively short period of time.  This test remains experimental.  Therefore, further studies with larger numbers of participants, conducted over longer periods of time, will be needed to confirm and validate the results.   If the results of this study are confirmed, this test could be used in conjunction with a less-invasive, initial screening test to help predict a person’s risk of cognitive decline and thus help people with PD to plan for the future.  

It could also help researchers to 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 study also lends support to previous research suggesting that in some cases the brain changes leading to cognitive decline are similar in Alzheimer’s disease and PD.

Reference: Siderowf et al. CSF amyloid {beta} 1-42 predicts cognitive decline in Parkinson disease. Neurology (2010) vol. 75 (12) pp. 1055-61 (http://www.neurology.org/content/75/12/1055.abstract).

Source Date: Dec 14 2010