Does any one here have Parkinson's? How many years has it been since you were diagnosed? Are you still programming? What advice would you give my friend?
Luckily we don't move a lot in this business. I might type slightly less quickly than most people (though I am actually quite a fast typist, I think it's slowing with age), and I might make more typos (thank goodness for IDE's which help correct things like that!) Ultimately I can code all day without much problem at all. Maybe other engineers are less tired at the end of the day, but who knows? I can only judge how I do based on my own experience.
The one big problem with Parkinson's is that it can have cognitive effects. I have read that it can cause dementia and other issues. This could obviously effect coding.
Anyway, I am glad to answer any questions.
Since those numbers are so low, there is right now a team at the Cleveland Clinic which recruiting for a much larger study (100 people total) that they're calling CYCLE: 40 people with PD will do forced exercise on a motorized stationary bike in the lab, 40 will do voluntary exercise on a normal stationary bike in the lab, and 20 will not be directed to exercise at all in the lab:
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4415238/
This is right now still in the recruiting stage so it probably has a couple years before it yields results; but if your friend can't live in Cleveland for a year, you could try to find another way to keep yourself at the 80-90 RPM levels, whether tandem biking with your friend or else by jury rigging a motor or perhaps even self-discipline.