When looking into MS in 2007, shortly after I was diagnosed. It was common belief and understanding that the further away from equator you went, the higher the prevalence of MS. To back up this it was often cited that countries like Australia, Canada and the UK had significant amount of people who had MS.
There was no real reason to doubt this theory, off course there were a few anomalies, but this was the general consensus.
When you look at the prevalence of MS in 2013, it seems as though this theory is being contradicted and more and more inconsistencies are being found in it.
This map related to the prevalence of MS in the 1960's
If we are to look at the latest map showing Global prevalence of MS 2008 (extracted from www.msif.org), we can see which countries and regions are most affected by MS.
It's interesting to see countries located in the Middle East, which are mainly on or very close to the equator, are seeing increased instances of MS. There can be a number of reasons for this:
1. They are getting better at diagnosing MS in this region
2. People affected by are more forthcoming and willing to be diagnosed
Whatever the reason, it still contradicts the idea that MS happens further away from the equator, I believe this is also linked to the Vitamin D theory. To say people with MS further away from the equator have low Vitamin D, due to the lack of sun is a fair argument, but if you live in the Middle East and have sun all year round, it contradicts the Vitamin D theory.
I accept people with MS have low Vitamin D and tests show this, I myself have low vitamin D and take tablets, but I don't believe this is the reason for my MS. It could possibly be part of the jigsaw, but not the reason.
Here is a quote from the US National Library of Medicine www.ncbi.nlm.nih.gov/pubmed/21463177
"Dubai should be considered as one of the regions with medium to high risk for MS, with prevalence rate higher than what has been previously believed. This high MS incidence and prevalence in Dubai is surprising and it may represent a true increase"
You can see from this that the world MS map is changing and as a result, established theories will have to be re-visited