AT RISK FOR MS - Clinical Conversion of Female Monozygotic Twins Discordant for CIS/MS

The definition of the most 'at-risk' population within highly susceptible groups would provide an opportunity for preemptive therapeutics. A convenient, safe, and tolerable therapy that delays the onset of clinical disease during the pre-symptomatic stage of demyelinating disease would provide a therapeutic alternative to a 'wait and see' approach in subjects at 'high risk' for CIS (clinically isolated syndrome - monosymptomatic demyelinating disease) or MS. Identical twins share the same genes and have the highest rate of shared MS. An identical female with a sister twin with MS has a 34% chance of having MS. Non concordant (no MS yet) identical (monozygotic - from the same sperm-egg zygote) female twins provide an ideal population to find out what factors predict the onset of MS in the non-affected twin. We will recruit 30 identical female twins, one with MS and the other without MS, and obtain brain MRI and biological samples on the non-affected twin and determine if: * the presence of characteristic MS-like lesion(s) on baseline MRI predisposes to MS. * specific proteins in blood or cerebrospinal fluid predispose to the clinical expression of demyelinating disease If we can predict by simple tests (MR brain scan and blood tests) the likelihood of the onset of MS in 'at risk' subjects, and have safe and tolerable therapies, we may be able to prevent the clinical onset of demyelinating disease (MS).