US-based Alexion Pharmaceuticals is paying $8.4 billion to acquire compatriot rare disease specialist Synageva BioPharma. The deal expected to close in mid-2015 has raised considerable interest because Synageva as yet has no products on the market.

The price tag, which includes $115 in cash and a portion of Alexion stock for each Synageva share, represents a premium of about 136% to the $95.87 closing price of Synageva immediately before the deal was announced, putting the total per-share price at about $226.

Alexion, which manufactures Soliris, a drug approved to treat the rare, life-threatening blood disorder paroxysmal nocturnal hemoglobinuria, said buying Synageva will help it accelerate and diversify its revenue growth while also expanding its manufacturing base.

The boards of the two New England companies - Alexion is based in Cheshire, Connecticut, Synageva in Lexington, Massachusetts - have already approved the takeover. Alexion said it has lined up $3.5 billion in financing from Bank of America Merrill Lynch and J.P. Morgan.

Synageva reported a loss of nearly $60 million for the first quarter of 2015, while generating $927,000 in royalty revenue. However, the biotech firm's pipeline of  drugs in development is said to be promising. One of its top prospects is Kanuma, which has been granted priority review by the US Food and Drug Administration.

The drug is aimed at treating lysosomal acid lipase deficiency, a disease that causes the buildup of fatty material in the liver and blood vessels and can cause serious health problems or death.

The FDA is expected to rule on the indication by September of this year, with a decision by European regulators at about the same time.