Research Provides First Whole Genome Map Of Genetic Variability In Parkinson's Disease

From Mayo Clinic

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.

Mayo Clinic and Perlegen Sciences will report their findings in The American Journal of Human Genetics. The paper was published online Friday, Sept. 9 (www.ajhg.org) and will appear in the November 2005 print issue.

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."

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.