University press release. The real science is too technical and boring, so the press release states the background of the research as the breakthrough, or makes wild unsupported speculative claims about applications, or both.
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".
> Scientists discover the loss of a substance called ‘myelin’ can result in cognitive decline and diseases like Multiple Sclerosis and Alzheimer’s.
MS is pretty much defined as degeneration of the myelin and that has been true for decades.