I have 2 boys, age 32 and 26 - both in "informed denial". They both have at the very least IBS. the youngest I swear is celiac and the oldest is showing signs of Crohn's.
We ran blood tests on the youngest about a year after I was diagnosed with celiac, which came out "very likely" but not a firm positive, so he refuses to take it serious - even in the middle of an episode. The oldest has had stomach aches his entire life and is recently showing signs of IBS, which could actually be crohn's developing, now that we know I have it. I call it "informed denial" because I made them sit and listen to me not long ago - it's not normal to feel the way they do. But they don't want to deal with it - yet, anyway.
Trying to be encouraging toward a better quality of life with them.