Five More Genetic Risk Variants Add to Understanding of Parkinsons Disease

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Parkinson’s Disease is one of the most common nervous system disorders of the elderly, developing most often in patients after the age of 50. When the condition occurs in younger people, genetic variants are usually the cause. Researchers had previously identified six genetic factors that affect Parkinson’s disease and now have found five more after studying over 7 million different possibilities.

A Total of Eleven Genetic Risk Factors Identified

Parkinson’s occurs when the nerve cells in the brain that make dopamine, a neurotransmitter that controls muscle movement, are slowly destroyed. Without the brain chemical, cells cannot properly send messages, leading to the loss of muscle function, involuntary tremors and movements, and muscle atrophy. Currently, there is no known cure for the disease that affects four to six million people worldwide.

In a collaborative effort by investigators in the US, UK, Germany, France, the Netherlands, and Iceland, a genome-wide association study involved data compiled from 5,333 Parkinson’s disease patients and 12,019 controls. It is the largest genetic analysis of Parkinson’s disease ever accomplished.

Read: Further Insight Into Causes of Parkinson's Disease

A total of 11 loci that “surpassed the threshold for genome-wide significance” were identified. Six had been previously identified as genetic risk factors: MAPT, SNCA, HLA-DRB5, GAK, and LRRK2. The newly identified five are ACMSD, STK39, MCCC1/LAMP3, SYT11, and CCDC62/HIP1R. These 11 variants account for 60.3% of the population-attributable risk for Parkinson’s disease in the study samples.

The researchers found that 20% of patients with the highest number of risk variants were 2.5 times more likely to develop Parkinson’s disease than the 20% of patients with the fewest number of genetic risk factors.

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Each of the five newly identified genetic variants is believed to affect neuronal activity or survival or is part of inflammatory pathways. Among the total eleven variants found, MAPT, HLA-DRB5, and MCCC1/LAMP3 had the biggest individual population-attributable risks.

Read: Deep Brain Stimulation May Stabilize Parkinson's Symptoms

But it is unlikely that these genetic variants act alone, say the study authors. There is likely an interaction between the genetic factors and there could be a role overlaid with someone’s ethnic background. Environmental interactions are also not completely ruled out.

“This study provides evidence that common genetic variation plays an important part in the cause of Parkinson’s disease,” the researchers write. “We have confirmed a strong genetic component to Parkinson’s disease which, until recently, was thought to be completely caused by environmental factors.”

Dr. Nicholas Wood PhD FRCP, FMedSci, head of the Department of Molecular Neuroscience at the UCL Institute of Neurology in London, said that right now, the potential implications of the discovery are “quite small”, but will lead to further investigations about the causes of Parkinson’s and may eventually help to find treatments that could cure or slow disease progression.

“However, a lot more work needs to be done on this,” comments Dr. Christine Klein of the University of Lubeck in Germany, who writes an accompanying editorial. “This is likely to take a few more years."

Source references:
International Parkinson Disease Genomics Consortium "Imputation of sequence variants for identification of genetic risks for Parkinson's disease: a meta-analysis of genome-wide association studies" Lancet 2011; DOI:10.1016/S0140-6736(10)62345-8.
Klein C, et al "From GWAS to clinical utility in Parkinson's disease," Lancet 2011; DOI:10.1016/S0140-6736(11)60062-7.

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