Researchers at the Perelman School of Medicine at the University of Pennsylvania and other institutions have uncovered a site of genetic variation that identified which patients with Parkinson’s disease are more likely to have tremors versus difficulty with balance and walking. The Penn team also found that patients with this genetic variation had a slower rate of Parkinson’s disease progression, and lower amounts of alpha-synuclein in the brain. Alpha-synuclein is a protein that experts know plays a role in the development of Parkinson's disease.

Clinicians have long noted that the presence of tremors, rather than balance and walking problems, as the initial or dominant symptom of Parkinson’s may suggest slower progression of the disease. The Penn-led study is one of the first to link this difference to a specific genetic variation. Tremor-dominant patients are also less likely to develop dementia, although this symptom was not assessed in the study.

The finding will be presented at the 68th Annual Meeting of American Academy of Neurology taking place April 15-21 in Vancouver.

“We have never understood the reason why some people present with more tremor vs. walking/balance difficulties in Parkinson’s disease,” said the study’s lead author, Christine A. Cooper, MD, a fellow in movement disorders at Penn Medicine. "This finding gives us information that may help to explain at least a small amount of the reason why people with Parkinson's disease have differences in terms of symptoms and progression, which has implications for future prognosis, treatment, and prevention efforts."

In the study, the investigators ranked 251 Parkinson’s disease patients at the University of Pennsylvania Health System on tremor and balance/walking scores. They then looked at the patients’ genotypes to see if there were correlations between ten genetic variations previously associated with Parkinson’s disease and the primary symptoms that the patients displayed.

The researchers found that 39 of the 251 patients who had a genetic variation known as the GG genotype at the rs356182 SNP 3’ to the SNCA gene were more likely to have: 1) tremors rather than walking/balance problems; 2) slower physical progression of the disease; and 3) lower levels of alpha-synuclein in the brain. Patients were followed up to seven years in some cases. The investigators carried out the same type of analysis with an additional group of 559 patients at three other clinical sites in the United States and found similar results for the association between the genotype and the type of PD symptoms.

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