Before you can start on this study, you will have what are called "screening tests." These tests will help the doctor decide if you are eligible to take part in this study. You will have a complete medical history and physical exam, including measurement of height, weight, and vital signs (blood pressure, temperature, breathing rate, and heart rate). You will have a neurological evaluation evaluating your strength and nerve function. You will be asked to report how a pinprick or a thin brush feel when applied to your skin. About 2 tablespoons of blood and some urine samples will be collected for routine tests. Women who are able to have children must have a negative urine pregnancy test.