STEVEN GALETTA, MD: By clinical definition, we have traditionally required that a patient have a clinical attack, say optic neuritis, and then separated by a month they have a second attack. So MS -- to fulfill the clinical standard definition of MS required two episodes of clinical attacks separated by a month.

We've come to recognize, however, that there is a group of patients who have a single attack, their first attack that are at high risk to develop MS and we have determined that by their MRI scan. Those patients who have had a single attack with an abnormal MRI scan are at increased risk of multiple sclerosis over both the short- and long-term.

As we've recognized that MS may, in the earlier stages, be quite silent, only evident on an MRI scan, we've pushed this treatment envelope to earlier and earlier. And in fact, many patients who have had a single attack who have a positive MRI scan are candidates for early therapy.