On a college application you want to be as honest and open as possible. It's your chance to allow the admission officer to know you. And as people, we like what we understand and know.
Your son's diagnosis has had an impact on his school and it's part of his story. His job on his application is to tell his story as truthfully as possible, including what he has learned about himself having to address this challenge.
Even though the Common Application main essay has only a suggested minimum of 250 words, and no upper limit, every admissions officer has a big stack to read every day; he or she expects to spend only a couple of minutes on the essay. Check best admission essay writing service online.