First large-scale whole genome map of genetic variability associated with Parkinson's disease

Mayo Clinic researchers in collaboration with scientists at Perlegen Sciences, Inc. and funded by the Michael J. Fox Foundation for Parkinson's Research have produced the first large-scale whole genome map of genetic variability associated with Parkinson's disease.

Their results highlight changes in 12 genes that may increase the risk for Parkinson's disease in some people. Parkinson's disease is a disabling and currently incurable disease that affects millions of people worldwide.

The findings are reported in The American Journal of Human Genetics.

"This represents one of the first large-scale whole genome association studies of any disease," said the study's first author, Mayo Clinic neurologist Demetrius Maraganore, M.D. "It is something we've wanted to do for years, and now we finally had the technology and funding to make it happen. If confirmed, the findings may lead to new insights about the causes of Parkinson's disease."

Significance of the Findings

Both the findings and the technology that produced them are groundbreaking, representing one of the most comprehensive genetic studies of Parkinson's disease to date with nearly 200 million genetic tests (genotypes) completed. To accomplish this, researchers initially studied the association of about 200,000 single-letter variations in the genome known as single nucleotide polymorphisms, or "SNPs" (pronounced "snips") in patients with Parkinson's disease. The study examined DNA from 775 people with Parkinson's disease (cases) and from 775 people without Parkinson's disease (controls).

"To be most effective, a whole genome association study requires accurate testing of a large number of SNP markers that are distributed across the human genome in a dense and informative pattern," says Dr. Maraganore. "In this respect, our collaborators at Perlegen have set a new standard."

"In one year, the Michael J. Fox Foundation and Mayo Clinic have generated results that will greatly focus future research efforts in Parkinson's disease," explained David Cox, M.D., Ph.D., chief scientific officer of Perlegen Sciences. "If replication of only one of these findings leads to a better understanding of the causes of the disease or improvements in the early detection or treatment of patients, we will have made significant progress."

Noteworthy findings include:

• Confirmation that variation in two previously known regions of the genome, PARK10 and PARK11, are likely associated with Parkinson's disease susceptibility.
• Identification of 10 additional SNPs that appear to be associated with Parkinson's disease susceptibility. Some of these are in or near genes with direct biological relevance to the disease. For instance, one of these, the SEMA5A gene, may play an important role in both the development and programmed death of dopamine-producing nerve cells in the brain. Selective degeneration of dopamine neurons in the brain is a hallmark feature of Parkinson's disease.

Susceptibility genes are genes that may make some people more or less likely to develop a disease but that do not necessarily cause the disease directly. The authors note that in this study, the size of the effect was small for any single SNP; combinations of gene variants or interactions with environmental factors may be necessary to develop Parkinson's disease.

"This study represents the first large-scale attempt to assess the contribution of genes to susceptibility and development of Parkinson's disease," said Kenneth Olden, Ph.D., Sc.D., chief scientific advisor for the Michael J. Fox Foundation and former director of the National Institute of Environmental Health Sciences (NIEHS) of the National Institutes of Health. "If confirmed, the finding of 12 potential susceptibility genes is significant. However, equally significant is the fact that this comprehensive study found no strong single genetic determinant of Parkinson's disease." The Michael J. Fox Foundation is organizing a large-scale validation study of the initial findings.