 The study doctor will test SB-509 60 mg and placebo. Everyone in this study will receive intramuscular IMdirectly into the muscle injections into both legs. This will happen 3 times over about 4 months. Two out of every 3 participants will receive SB-509 and 1 out of every 3 will receive placebo. You will not know, and the study doctor will not know, whether you will receive SB-509 or whether you will receive placebo. 