@szelisk Collagenous colitis is microscopic colitis. There are two types of microscopic colitis: Collagenous colitis and Lymphocytic colitis. They are both under the name of “microscopic colitis”.

@szelisk There was only one reference from 2016 indicating that LC doesn't show a genetic component(s) and it was not the research focus for that paper, so not enough to rule out HLA or other genetic associations for LC. LC is considered by some an earlier stage of collagenous colitis (CC) (both are microscopic colitis). When my MC was diagnosed 10/2017 there was almost no peer-reviewed research on CC (still not much). I have celiac (17 years) with HLA-DQ8 0302, so a likely link. The celiac was probably triggered by H1N1 followed a few days later from the stress of some guys trying to murder me. The GI that did the celiac scopes and biopsies was 6 mo after the start of celiac so minimal damage to intestinal villi; he screwed up because he was convinced that I didn't have celiac due to absence of anemia, and decided I instead have diverticulosis (still negative). He only had me off gluten for a week and just one small intestine biopsy. So, it took CC to convince the doctors that, yes, I have celiac. Having HLA-DQ8 wasn't enough because around 3-8% of the population has that. We really do need to advocate for ourselves. I'm a 72 yo retired research scientist. As an aside, the GI did find rather nasty gastric reflux damage to my esophagus that I didn't know I had. It was clear on the endoscopy 5 years later and the GI and nurse were surprised that all I did was go gluten free (and sleep on my left side more).