Thanks to BleachGate, this is probably the first time many of you all in the Skeptical Community have heard about Crohns Disease (SPOILER: kid with Chrons gets booted from a ‘support’ forum for speaking out against woo-‘treatments’).
Crohns is an inflammatory bowl disease (IBD), where your guts do fun things like shrink until your bowls are obstructed, or your body decides you need more passages out of your intestines (Google ‘fistula’. I dare you.), and some times you just good-old-fashioned poop blood. So, dont confuse IBD with IBS, and dont get me started on IBS.
Crohns is the usual grab-bag of ‘What causes this disease?’ Yeah, there are genes that have been associated with Crohns– about 30. But just because you have the genes, or any particular collection of genes, doesnt mean you are going to get Crohns. Some people have correlated Crohns with diet, or smoking, or oral contraceptives, or E. coli… We just dunno what causes this disease yet.
Well a friggen NEATO paper came out that might help treat Crohns, but definitely helps illustrate how complex this stuff is:
Virus-plus-susceptibility gene interaction determines Crohn’s disease gene Atg16L1 phenotypes in intestine.
They have a mouse model that has one of the ‘Crohns susceptible’ genes. That mouse does not develop mouse Crohns on its own.
When that mutant mouse is infected with a mouse norovirus, the mouse gets mouse Crohns!
You have to infect the mutant mouse at just the right time (virus, then induce some inflammation) for it to get mouse Crohns. If you induce inflammation and infect at the same time, the mouse is fine.
If you infect that mouse with a different kind of mouse norovirus, its fine. Timing doesnt matter.
Oh… and intestinal bacteria have a hand in this too (if you give the mice antibiotics, the pathology isnt so bad).
So you have to have 1) the ‘right’ genes, with 2) the ‘right’ virus, at 3) the ‘right’ time, with 4) the ‘right’ commensals for this mouse to develop a pathology similar to human Crohns Disease.
Not everything is as simple as “Disease X is caused by a mutation in Gene X”, or “Disease Y is caused by infection with Pathogen Y”. Sometimes, disease is just an awful, awful slot machine.