MS is a catch all. Multiple causes can result in demyelination even if the mechanism is the immune system. You have MS if you have demyelination products detectable in your spinal fluid and have lesions on the spinal cord. Whether it's a genetic, environmental, or some other underlying condition clearly varies, for instance the version that I have is almost certainly genetic because of family history but plenty of other people get it with no family history.

But I think people are pretty sure that certain B cells are the easiest to interrupt culprit, my current medication literally just kills a specific B cell and that treatment last six months. Take from that what you will.