Recently spoke with a "genetic counselor" associated with the program about all this. She seemed to be concerned that I might not be able to put the probabilities in the proper perspective. Apparently I have about a 7% chance of getting PD by age 80... which is a lot more than the gen pop, but nothing I'm going to worry about especially since I'm already 56.
This is my category:
Alterations in certain genes, including GBA and UCHL1, do not cause Parkinson disease but appear to modify the risk of developing the condition in some families. Variations in other genes that have not been identified probably also contribute to Parkinson disease risk.
I figure if I'm going to get it I'm going to get it - participating in the study isn't going to change that (although conceivably I might find out earlier than I would otherwise). I'd rather know than not know. I'm glad it's not something a lot worse - I suppose people would have a lot harder problem emotionally with other diseases and higher probabilities.
I'm getting thank you e-mails from all kinds of people involved in the research - it's almost embarrassing because I really haven't done anything except agree to some interviews and maybe an exam at some point in the future.