US-based Alexion Pharmaceuticals has signed an agreement to acquire biopharmaceutical firm Synageva BioPharma for around $8.4bn.

Under the deal, Synageva will receive consideration of $115 in cash and 0.6581 Alexion shares, for each share of Synageva, representing a total per share value of $230 based on the nine day volume-weighted average closing price of Alexion stock through 5 May.

Alexion Pharmaceuticals CEO David Hallal said: "Synageva is an ideal strategic and operational fit for Alexion that aligns with what we know well and do well, providing life-transforming therapies to an increasing number of patients with devastating and rare diseases."

"Synageva is an ideal fit for Alexion that aligns with what we do well, providing life-transforming therapies to patients with devastating and rare diseases.

Synageva includes protein therapeutic programmes for rare diseases with unmet medical need, and they are currently at various stages of development.

The company plans to launch Kanuma for the treatment of lysosomal acid lipase deficiency (LAL deficiency), and is enrolling patients in a Phase I / II trial with its second, first-mover programme SBC-103 for MPS IIIB.

Kanuma is currently under priority review with the US Food and Drug Administration (FDA), and has granted accelerated assessment of its marketing authorisation application (MAA) by the European Medicines Agency (EMA).

It also received breakthrough therapy designation by the FDA for LAL deficiency presenting in infants.

Synageva’s first-mover programme SBC-105 is an enzyme replacement therapy in preclinical development for disorders of calcification and it recently produced enzymes targeting Hunter syndrome, Fabry disease and Pompe disease, with expression levels and activity that support further preclinical development.

Synageva BioPharma president and CEO Sanj Patel said: "Alexion is uniquely suited to advance Synageva’s mission to deliver life-saving therapies to patients whose diseases were once considered too rare for developing treatments."

Subject to customary closing conditions, the deal is expected to be completed in the middle of this year.