Researchers need to know the genetic profiles of their study participants to understand more about how certain mutations manifest disease. But do the participants have to know?

A group of 35 Parkinson's disease (PD) researchers published today in Genetics of Medicine the different answers to that question among sites investigating mutations in the LRRK2 gene, the greatest known genetic contributor to PD. Investigators from The Michael J. Fox Foundation-sponsored LRRK2 Cohort Consortium authored the letter to the editor.

The consortium spanned nine countries on four continents. People with Parkinson's and their family members were screened for a LRRK2 mutation, and researchers conducted a more thorough investigation on carriers and a subset of those without mutations.

"The study design raised an ethical question: Should the genetic testing results be reported to participants?" the authors wrote. People with PD who carry the mutation are not treated differently than non-carriers with PD, and there are no preventative therapies to offer people with the mutation who do not have PD.

Parkinson's is a progressive, neurological disorder with no proven preventive or disease-modifying strategies available. In general, mutations in the LRRK2 gene account for less than five percent of PD cases, but that number jumps in certain ethnic populations; LRRK2 mutations are associated with 18 to 40 percent of PD cases among those of Ashkenazi Jewish or North African Berber descent. Adding to the complexity is the unknown "penetrance" or association between a mutation and disease onset; estimates range from 24 to 80 percent.

LRRK2 Cohort Consortium sites in the United States did not offer genetic results to participants with PD, but Israeli sites concluded it would be unethical not to provide such information and therefore informed all PD participants who requested their results. Most study sites did not offer results to non-PD participants unless they first received genetic counseling. The Toronto team stopped offering these results after they felt participants had trouble grasping the information.

The letter's authors outline the arguments for each side: Knowing one's genetic risk may be distressing. However, many feel that this data is the property of the participants and they should be allowed to receive or refuse it as they prefer.

"It is true that presently there is no definitive action one can take to offset genetic risk for Parkinson's disease," said Brian Fiske, PhD, vice president of research programs at The Michael J. Fox Foundation. "However, individuals who do choose to learn their genetic status can play an important role in teaching researchers about the disease and possible treatments."

With divergent opinions on this emerging practice and legislation in play, the authors encourage researchers to seek a consensus. They wrote: "Collecting data on what patients and families know and understand about genetics and about the kind of data they would like to receive will help guide future policy making."