The further north you go, the more cases of MS.
I do not know if that statistic occurs globally, or not.
My female cousin, born and raised in northern Michigan, died from exceptionally aggressive MS in the 1980s. She was a completely healthy young woman in her mid-thirties. Three years after diagnosis, she was dead. She literally had the best MS care in the world at that time at the Mayo Clinic.
Today, MS medications have improved so much that almost no one dies from it anymore, and many MS victims are able to lead an almost completely normal life.
I suspect that the mechanism which enables the genetic variability cited with these migrations involves the susceptibility to prion replication, and that is responsible for the increased incidence of MS and Alzheimer’s disease. UC San Francisco researchers have associated Alzheimer’s disease with attack by two successive prions. I suspect that, if researched, MS would go a similar route, especially since MS is autoimmune. The human immune system attacks things which it recognizes as foreign.
https://www.ucsf.edu/news/2019/05/414326/alzheimers-disease-double-prion-disorder-study-shows
https://www.ucsf.edu/news/2001/08/97139/ucsf-study-finds-two-old-drugs-may-help-fight-prion-diseases
I certainly cant say that it doesnt.
There may be something to it but not necessarily in the way you exactly meant.
Looking at the patterns of country of origin and settlement in the US shows that to a degree different Europeans settled at different latitudes in the US. For example, Germans settlement was and is to this day most prominent starting in Eastern Pennsylvania and runs in a band westward and up into Michigan and Wisconsin while English and Scots tended to be further South.
The latitude relationship, if it does exist, may have been transferred from Europe and still exist while becoming mixed and muddled due to the inter-settlement of pockets of different peoples here in the US.
So that study would almost have to start in Europe and work back from there to see if it was related to genetics rather than latitude.