Genzyme Rejects Sanofi-Aventis' $18.5 Billion Offer By: MarketMinute.com Stock News August 30, 2010 at 17:45 PM EDT Genzyme Corp. (Nasdaq: GENZ) rejected Sanofi-Aventis' $18.5 billion acquisition offer as too low. Shares of Genzyme climbed $2.29 to close at $69.91.