Here is some information on finding a study to join that might help.
--- Is Mayo Clinic doing research on my condition?: https://www.mayoclinic.org/patient-centered-care/mayo-clinic-doing-research-on-my-condition.

Here's are some studies listed for the Rochester area:
--- Primary Care in Rochester and Kasson: https://communityhealth.mayoclinic.org/find-a-study

He was asked to join by his doctor at Mayo. I think you can inquire if there are any clinical studies available.