In this study, a proportion of subjects will receive study agent at its recommended dose and interval (45mg for subjects less than or equal to 100kg, or 90mg for subjects greater than 100kg; every 12 weeks after 2 starter doses at Weeks 0 and 4). The majority of subjects will have the opportunity to receive study agent less frequently during the randomization period depending on the subject's response. The study consists of a 4-week screening period; a 28-week open-label run-in period; a double-blind treatment period from Week 28 to Week 104; a 12 week post-treatment period; and a 20-week safety follow-up. Participants will be randomized for the double blind period into one of two study groups. Group 1 participants will receive an injection of the study medication at a 12 week dosing interval. Group 2 participants will undergo a placebo withdrawal and may receive study agents at an extended interval greater than 12 weeks. During the double-blind treatment period, subjects in Groups 1 and 2 will receive placebo as necessary to maintain the blind.
