MS is an autoimmune disease - the immune system attacks the body. Risk factors are not exactly known, but involves genetic, environmental and viral factors at least. MS is sex biased (more female get it) and age biased (starts usually between 20 and 40 years of age). I do not think ethics matter - acquiring the disease is pure unluck, but ethnicity matters (affects more white northern Europeans).
Neanderthal genes might be contributing - they boosted the immune system of white northern Europeans, while also increasing the risk of allergy and autoimmune diseases: