This study consists of a 12-week base study (MK2578-003-AM03) and an optional 40-week extension study (MK2578-003-EXT12). Participants who complete 12 weeks of treatment in the base study will enter the extension on the most recent dose administered in the base study or a newly adjusted dose, if adjustment is required to bring Hg levels within range. Participants' doses of MK2578 will be adjusted upward or downward during the extension study to maintain Hb in the range of 10-12 g/dL.