Shire Plc has agreed to buy U.S. rare disease specialist Dyax Corp for about $5.9 billion – and potentially up to $6.5 billion – while still pursuing a five times larger unsolicited bid for Baxalta Inc. It comes amid a record wave of deal-making in the broader healthcare sector so far this year, which amounted to $477 billion as of last week, according to Thomson Reuters data. Shares in the U.S. biotech firm jumped to $36.75 in premarket trading on Monday, while Shire’s stock in London fell 0.5 percent.