I found this post which may be the one you've referred to earlier.
Its an article by Asthon Embry (best bet diet site). According to Embry, research into epidemiology of MS provides a number of important constraints for the interpretation of an environmental factor as the main cause of MS.
Here are the constraints Embry identified for any proposed environmental factor, I've copied from the article, but just added numbers. And yeah, there are nine.
1- It must be found throughout the world but be specific enough to affect only half or less of the susceptible individuals.
2- It must affect immigrant children more than it does immigrant adults. On the other hand it must affect susceptible identical twins mainly when they are adults rather than when they are children.
3- It must be much more common or effective in northwestern Europe, Canada, United States, Australia and New Zealand than in the rest of the world.
4- It must be more common or effective in higher latitude areas so as to create a pronounced north/south gradient of MS prevalence.
5- It must have enough variation so as to create significant MS prevalence and incidence differences within ethnically homogeneous populations over relatively short distances.
6- In Hawaii it must adversely affect those of Japanese origin whereas at the same time have a positive effect on Caucasians.
7- It must be transportable so as to explain the sudden increase in MS prevalence in the Faroes following British troop occupation during World War II.
8- It cannot be transmitted by either person to person contact or by a blood transfusion.
9- It must be increasingly more widespread and effective over the last 100 years.