Yesterday, Sanofi-Aventis SA’s top executive, hours after squaring up an agreement of buying Genzyme Corp. for $20.1 billion plus potential additional payments, promised to protect the Genzyme brand, but he never guaranteed to keep all of the company’s four thousand five hundred Massachusetts jobs.

The Genzyme name that can be seen on the top of this building is going to be there tomorrow, a year from now, and ten years from now, stated Sanofi chief executive Christopher A. Viehbacher at Genzyme’s Kendall Square headquarters shortly after being introduced by Henri A. Termeer, his Genzyme counterpart, to employees,

Viehbacher asserted that the French drug maker isn’t emphasizing on making cuts at Genzyme, the largest biotechnology company of Massachusetts, but considers it as key to Sanofi’s efforts to expand its presence in the United States and in personalized medicine. Eventually, Genzyme will become the center for Sanofi’s business producing drugs that treat rare diseases. The Cambridge based biotechnology firm’s success has been built on its expensive treatments for genetic diseases by which a relatively small number of people all over the world get affected.

Viehbacher, in a later interview, stated that changes are coming to Genzyme as a result of the merger. It should be apt to say there are going to be some cost savings along the way, stated Viehbacher. But one wants to be careful in terms of risk of disruption. It may be that the firm reduces in some areas, but that it invests in other areas.

On top of its global headquarters, Genzyme Center, the company has another office in Cambridge. It has some major manufacturing sites in Allston and Framingham, a smaller Cambridge production site, research and development operations in Waltham and Framingham, and a distribution center in Northborough.