Credit: Marzanna Syncerz

Loss of myelin underlies several disorders of the central nervous system (CNS) in humans, the most well known of which may be multiple sclerosis. Multiple sclerosis affects roughly 2.5 million people worldwide and can cause a range of symptoms including fatigue, loss of coordination and balance, numbness, blurred vision or blindness and even paralysis. It is thought to be an autoimmune disorder in which the immune system mistakenly attacks the body's own healthy tissue, destroying the myelin that surrounds nerve fibers of the CNS and interfering with transmission of nerve signals. There is no known cure for multiple sclerosis, although various treatments are available to help manage its symptoms and progression. Restoration of damaged myelin is thought to help protect nerve fibers from further degeneration and to restore signal transmission but, until now, had not been shown to result in functional recovery. New research from Ian Duncan (University of Wisconsin, Madison) and colleagues now suggests that remyelination can indeed restore function in cats suffering from neurological demyelination.

Pregnant cats had been fed an irradiated diet as part of a study evaluating the effects of irradiated food on feline growth and development. After approximately 4 months on the irradiated diet, some of those cats developed severe progressive neurological dysfunction, including movement disorders, vision loss and paralysis. They were found to have widely distributed demyelination of the CNS, but nerve fibers remained intact. The cause of demyelination in the cats could not be identified. Biochemical analysis of the diet and of tissues from the affected cats showed no nutritional deficiencies or toxicities. The cats were put back on a normal diet and recovered slowly; after 2–4 months, they were neurologically normal. Examination of the CNS showed extensive remyelination, particularly in the optic nerve (Proc. Natl. Acad. Sci., published online 2 April 2009; doi:10.1073/pnas.0812500106). The restored myelin sheath was thinner than normal but seemed to have normal physiological function.

The results of this study confirm that restoring damaged myelin in the CNS can restore function, provided that nerve fibers are preserved. “The fundamental point of the study is that it proves unequivocally that extensive remyelination can lead to recovery from a severe neurological disorder,” explained Duncan. Duncan also noted that it is unlikely that irradiated food would have similar effects on human development, as the effects seem to be species-specific; pregnant rats fed an irradiated diet did not develop any neurological dysfunction.