A neurodegenerative disease affecting between 1 and 2 percent of people over the age of 65, Parkinson's disease can be difficult to diagnose as no definitive test exists. Its symptoms, which include tremors, sluggish movement, muscle stiffness and difficulty with balance, can be caused by many other things, including other neurological disorders, toxins and even medications.

Up until about twenty years ago, late-onset Parkinson's disease was thought to be caused exclusively from environmental factors. Even after researchers determined the disease to have genetic components - previous studies had only helped to confirm that genes previously had been found to confer "risk".

This new study took 18 years to build, and studied more than 4,000 individual DNA samples - half from unrelated patients with the disease, and the other half from healthy 'controls'. Patients from whom samples were taken were tracked for at least a dozen years after their initial diagnoses to assure that they indeed had Parkinson’s.

The teams meticulous selection of patients, and extreme care in the handling of DNA samples has resulted in confirmation that a gene from the human leukocyte antigen (HLA) region is strongly linked with Parkinson's disease. This genetic finding demonstrates that inflammation isn't simply a result of having the disease, but somehow is involved as a key player in its origin.

This long-term Genome-wide Association Study involved a global consortium, including Johns Hopkins researchers from the Center for Inherited Disease Research. This new data was published in the August 17th edition of Nature Genetics.

“This is an exciting finding from a genome-wide association study (GWAS) which is completely hypothesis-independent and bias-free, based solely on looking at the whole genome and finding out what genes might be related to Parkinson’s,” says Kimberly Doheny, Ph.D., assistant professor, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University School of Medicine; assistant director of the Center for Inherited Disease Research (CIDR); and director of the CIDR Genotyping Lab, Johns Hopkins University.

The study’s principal investigator, Haydeh Payami Ph.D. commented; “We now have another window into what may be going on in Parkinson’s. This finding anchors the idea of immune system involvement in genetics and brings it out to the forefront in terms of where research should be directed.”

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