Two studies to try to uncover genetic associations behind Parkinson's disease have found that people with certain gene mutations could have a higher risk of the disease.

Parkinson's disease, which affects about 1.5 million Americans, is a progressive neurologic disorder caused by the degeneration of nerve cells in the portion of the brain that controls movement. The likelihood of developing Parkinson's disease increases with age and involves a combination of environmental risk factors and genetic susceptibility. There are currently no treatments that can slow down or halt the progression of Parkinson's disease.

An international study pooled nearly 14,000 DNA samples and data to confirm that mutations in the alpha-synuclein (SNCA) gene and microtubule associated protein tau (MAPT), both present in the general population, are risk factors for sporadic Parkinson's disease.

In another study from Japan, researchers also identified a different combination of genetic variants as risk factors for Parkinson's disease in people of Japanese descent.

These are the largest genome-wide association studies (GWAS) reported to date involving Parkinson's disease. GWAS studies look in the DNA on all of the chromosomes in a specific population of individuals for common genetic associations with a disease.

"Because previous Parkinson's GWAS were too small and lacked power, we worked together to compile and analyze the large data sets needed to identify the elusive genetic variations that play a role in this complex disease," said Andrew B. Singleton, who co-led the study with Thomas Gasser. "With this better understanding of the underlying genetic variants involved in the progress of this disorder, we have more insight into the causes and underlying biology of this disease. We hope this new understanding will one day provide us with strategies to delay, or even prevent, the development of Parkinson's disease."

The two-phase GWAS first analyzed DNA samples of 1,713 people with the disease and 3,978 free of the disorder, all of whom were Europeans. The findings were then replicated in a similar group of 3,361 people with Parkinson's disease and 4,573 without the disorder. Following the initial findings implicating SNCA and MAPT variants as risk factors for typical Parkinson's disease, the team then compared results with researchers performing a GWAS study in a group of Japanese people (2,816 with Parkinson's disease and 3,401 free of the disorder). This second GWAS also revealed the strong association for SNCA but not for MAPT. Additionally, both GWAS studies found evidence for two additional risk variants; the first, which was strongest in the Japanese population, was named Park16; the second is close to a gene, LRRK2, which Dr. Singleton's and Dr. Gasser's groups previously found contains mutations that cause an inherited form of Parkinson's disease.