maybe helps
IBD is on the rise in any country that becomes Westernised, China, Japan, Korea, North Africa, Eastern Europe, regardless of latitude.
What's interesting is that UC precedes Crohn's disease in many countries, so you get a rise of UC in those countries, and the rise of crohn's disease follows like 10 year later.
Also interesting, and they've shown this many times, that if you look at immigrants who come to the West and compare them to people who stayed in a low-incidence country, those immigrants will have a far higher incidence of crohn's disease than the same people, from the same gene pool, who stayed in their own country.
They've seen this in African tribes where they had 0 crohn's disease, they come to the West and they get crohn's disease. They've seen this with Indians, who come to the UK, they get crohn's disease, meanwhile the people who stayed in India, same gene pool, have a very low incidence.
The genetic link is there in the West, but it's not very strong, it's one rather small factor, a factor that doesn't even come into play in Asia where people are getting crohn's disease without genetic markers. Even with exact twins, the rate is not 100 percent, it's below 50 percent, and it's even lower if you split up the twins, so you can ask yourself if the fact exact twins live together isn't contributing to the fact both got crohn.
Also, genes don't explain the rise of crohn's disease anymore, something is going on with how we live or an agent in the environment is contributing to the rise unrelated to genetics.
If genes had a strong connection to crohn's disease the rate would be steady, you wouldn't have exponential increases like is happening now, genes aren't an explanation for crohn's disease, they only result in predisposition.
http://ibd.ads-netlink.com/IBD/pdf/special/5.pdf
IBD: