@Kat919 - Myelin makes signals travel faster. Basically, myelin wraps around the neuron in several strips sort of. The nerve signal jumps from one gap to another by saltatory conduction instead of having to travel slowly. Problems with the myelin sheath cause neurons to fire more slowly, which is very bad.
Lorenzo's Oil was based on a true story of a boy who had a leukodystrophy. That's a disease that comes in several forms - he had the worst form, which attacked the neurons in his brain. The oil does seem to slow down or prevent the disease.