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Genetic Parkinsonís May Progress More Slowly

People who develop Parkinson’s disease (PD) because of mutations in a gene called parkin better retained movement and cognitive abilities after years with the disease, than did people with non-inherited PD, according to a new PDF-funded study published online November 4 in JAMA Neurology. This finding suggests a slower progression of parkin-associated PD, which may help people with parkin mutations who develop the disease at an early age to prepare for the future.

While the majority of people with PD do not develop the disease because of genetics, a small number of people do. For example, in people with young onset PD (those in their 20s, 30s and 40s), sometimes the disease is caused by mutations in the parkin gene. People with these genetic mutations experience the disease similarly to those without the mutation – exhibiting some of the same symptoms, such as tremor, and showing neuron loss in the same region of the brain. 

However, doctors and researchers have noticed differences between this form of genetic parkinsonism and sporadic PD. For example, the motor symptoms of people with parkin mutations are often not as severe, and are better controlled over the long-term with levodopa, than are the symptoms of people with sporadic PD. Also, Lewy bodies, the clumps of protein that are a hallmark of sporadic PD, are rare in the brains of people with parkin mutations. These observations led researchers to wonder if people with parkin mutations better retain cognitive abilities, than people with sporadic PD.

To help answer this question, Roy Alcalay, M.D., at the PDF Research Center at Columbia University Medical Center, collaborated with colleagues at Columbia and at 16 sites in the US that are part of the CORE PD (Consortium On Risk for Early-onset Parkinson's Disease) study. Together, they compared the cognitive and motor symptoms of 44 people with early-onset PD. All participants had lived with PD for more than 14 years. Twenty-one had mutations in the parkin gene, while 23 had no mutations in any PD-associated genes (sporadic PD).

Results

  • Although all of the people in the study had early-onset PD (diagnosed at age 50 or younger), people with parkin mutations developed their disease about 13 years earlier and were younger at the time of examination than people with sporadic PD.
  • People with parkin mutations scored better on neuropsychological tests that assessed aspects of cognitive function, including memory, attention, and executive function, than people with sporadic PD; they were able to shift their attention between different tasks more swiftly.
  • People with parkin mutations were less likely to experience mild cognitive impairment and dementia than those with sporadic PD.

What Does It Mean?

PD is a diverse disease, in terms of age of onset, rate of progression and prognosis. Scientists, in working toward the goal of personalized medicine for PD, have been trying to identify genetic markers that may explain these differences among people with Parkinson’s.

To date, the most success in identifying different types of PD has been achieved with parkin associated PD. While there were anecdotal observations that the symptoms of people with parkin mutations were less severe than sporadic form of PD, this is largest, most comprehensive and first systematic study to compare the cognitive and motor symptoms between the two groups over the long term (more than 14 years after PD diagnosis). 

This study confirms these anecdotal observations, finding that although people with parkin mutations developed PD earlier, they performed better on various tests of cognitive and motor function, and they were less likely to develop dementia, many years after PD diagnosis.  One weakness is that the study is cross-sectional, meaning it looks at people at with PD at one moment in time, with about 10 years difference in average age between the two groups. In the future, scientists should study two groups of similar ages over times.

These results will help people whose PD is caused by a mutation in the parkin gene, along with their families, to better understand how their disease may progress and to prepare accordingly. For example, people who carry parkin mutations may worry about their risk of dementia and their long-term ability to work. These results may provide reassurance that their disease progresses more slowly and they have a lower risk for dementia than people with sporadic PD.

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Reference: Alcalay RN et al. (2014) Cognitive and Motor Function in Long-Duration PARKIN-Associated Parkinson Disease. JAMA Neurol 71:62–67.  DOI: 10.1001/jamaneurol.2013.4498  http://dx.doi.org/10.1001/jamaneurol.2013.4498

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Source Date: Jan 24 2014