Balance?

This is our first time on line with you all. Our son will be 39 years old on Sunday. I do not know of anyone in our situation, but here is David’s (our son) story. For at least 20 years now he was able to walk and run independently. For this past year he has had decrease balance. Now he can only stand with support, and if alone will crawl. He has been seen by the specialist and has had MRIs blood test but nothing comes up to give us any answers. Has anyone had any experience with this situation with their son or daughter?
Love to hear from you,
Thanks,
Mimi and Randy Whitney