While pernicious anemia and MS affect different body systems are not related, there is a factor that is common to both of them: vitamin B12 deficiency.
In pernicious anemia, the body can't make enough healthy red blood cells because it doesn't have enough vitamin B12. The deficiency can come from malabsorption due to a lack of a specific protein or various problems in the intestinal tract, or lack of B12 in the diet.
In a different manifestation, B12 deficiency is one of the two great mimics of MS (Lyme disease being the other). B12 deficiency and MS share common inflammatory and neurodegenerative characteristics. The signs and symptoms of the two are so nearly identical (right down to demyelination and brain lesions) that telling them apart is sometimes difficult. B12 plays a role in the formation and maintenance of myelin, so a deficiency can lead to demyelination. But B12 deficiency is just a mimic, it isn’t MS.
However, this is where it gets more interesting and more complicated. Studies have shown a significantly higher rate of vitamin B12 deficiency in people with MS than in people without MS. Researchers suspect that MS somehow involves problems with the metabolism of B12 and that there may be some causal relationship between MS and B12 deficiency (that’s MS and B12, not MS and pernicious anemia). Time – and more research -- will tell.