[elric]

The word "discover" is a bit of a stretch here, but I suspect they mean that the "discovery" was that the loss of myelin is a part of age-related cognitive decline as well as MS.

But MS is not the only disease is in which demyelination occurs, not by a long shot. Even the definition of MS (when it comes to getting a diagnosis) is a lot more complex than just "degeneration of myelin".