FDA has rejected Genzyme's application to produce large-scale quantities of Myozyme, an analog of a human enzyme to treat Pompe disease, a rare inherited metabolic disorder. Genzyme currently has approval to sell Myozyme produced at the 160-L scale but wants to make the drug in 2,000-L vats. However, the agency says there are differences in the carbohydrate structures of molecules made at smaller and larger scales, and it therefore considers the end products to be two different drugs. Genzyme will be required to file a separate biologics license application for the 2,000-L process, which will push back commercialization of the large-scale material to the first quarter of 2009. Genzyme lowered its 2008 sales forecast for Myozyme to $275 million to $285 million from $320 million to $330 million. More broadly, FDA's request for more Myozyme data could signal a tough road for firms hoping to launch biosimilars, generic versions of biologic drugs. Although there is no formal route for approving biosimilars in the U.S., many generics companies are investing in technology to participate in what they hope will be a robust market.