The mood for mega deals in the pharmaceuticals sector shows no sign of abating, as Alexion unveils plans to buy Synageva BioPharma for a whopping $8.4 billion.

The move sees Alexion, which currently has just one drug - the hugely expensive Soliris (eculizumab) - on the market, delve much deeper into the rare diseases field, an increasingly popular target for bolstering R&D pipelines as the blockbuster era recedes into the distance.

Alexion has laid on the table $115 in cash and 0.6581 of its shares, equating to around $230 per Synageva share, which is more than twice its current value. But “while some investors may be picking their jaws off the floor at such a valuation, we note that Synageva has only disclosed a fraction of its development efforts,” noted Baird Equity Research analyst Christopher Raymond, according to Reuters.

The purchase of Syngeva gives Alexion access to lead product Kanuma (sebelipase alfa), which has been filed in the US and European Union for LAL deficiency and is expected to launch this year alongside the firm’s own Strensiq (asfotase alfa) for hypophosphatasia.

In total, the combined pipeline will have eight highly innovative product candidates in the clinic for eleven indications, as well as more than 30 diverse preclinical programs across a range of therapeutic modalities, representing “the most robust rare disease pipeline in biotech,” says Alexion.