Biotechnology company Biogen Idec Inc. said Thursday it is buying privately held Syntonix Pharmaceuticals Inc. for $40 million, with a possible additional $80 million in payments for development milestones.

The deal is expected to close during the first quarter.

Biogen will maintain Syntonix's 25,000-square-foot Waltham, Mass., facility. Both companies boards have approved the buyout.

Syntonix's lead product, FIX:Fc, is a treatment candidate for hemophilia B. The company focuses on using technology to develop inhalable treatments. The company plans to apply with the Food and Drug Administration to begin clinical trials in 2007.

"With this transaction, we continue to deliver on our strategic initiative to enhance our pipeline and expand into additional specialized markets," said James C. Mullen, Biogen Idec's president and chief executive.

Shares of Biogen shed 37 cents to $48.91 in morning trading on the Nasdaq.