Is the cause of Multiple Sclerosis really unknown?

Multiple Sclerosis is where one's immune system attacks the fatty coating
around the nerves.  But if someone eats under 20 grams of fat a day their
symptoms are not as bad.  Maybe what is happening the immune system is
attacking a fat that's an allergen, but inadvertently attacks the fatty
tissue around the nerves.  Does anyone know of an allergen fat that may be
playing a role in MS?

I just found out my aunt has MS, which has been a family secret for the last
10 years (after knowing other people with it) and I'm sick of the secrets
and I find it inacceptable that the cause of MS is unknown.