PARIS ( TheStreet) -- Sanofi-Aventis ( SNY) said Wednesday it agreed to buy U.S. biotechnology company Genzyme ( GENZ) for $74 a share cash, or $20.1 billion.

The merger is expected to close early in the second quarter of 2011, the companies said in a press statement.

Each Genzyme shareholder also will receive one contingent value right for each share they own, entitling the holder to receive additional cash payments if specified milestones related to Lemtrada, Cerezyme and Fabrazyme are achieved, French drugmaker Sanofi said.

"This agreement with Genzyme is both consistent with our long-term strategy and creates significant long-term value for our shareholders," said Christopher Viehbacher, Sanofi CEO. "This transaction will create a meaningful new growth platform for Sanofi-Aventis while expanding our footprint in biotechnology."

Sanofi said It expects the deal to be accretive in the first year following its completion.

Genzyme shares closed Tuesday at $74.30 on reports the deal was imminent.

-- Written by Joseph Woelfel

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