Few autoimmune disorders are more challenging for patients than multiple sclerosis, a progressive condition that can affect vision, impair the ability to walk, cause extreme bouts of neuropathic pain, and tends to strike women at three times the rate of men.

New findings from a large team of researchers in Germany involving twins may provide the clearest insight to date illuminating the role of cytotoxic T cells—CD8+ T cells—in the progression of multiple sclerosis, also simply referred to as MS.

The disorder is a chronic autoimmune disease of the central nervous system characterized by the immune system’s assault on the protective myelin sheaths of nerves. Irrevocable demyelination—loss of the fatty insulation surrounding nerves—interferes with the conveyance of nerve impulses between brain and body. Medicines can help control the disease, slowing progression and easing pain, but there is no cure.