Honestly, I think the reason why it's skipped over a bit is because it's not quite as lethal as cancer, and it doesn't really appeal to anyone else than people with it and people that know other people with it.
Yeah, it's not lethal, but it's painful, debilitating, and currently expensive. The treatments involve decreasing your immune system down to a point where it won't attack your intestinal tract anymore, allowing you to become sick really easily.
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