Roche has increased its offer to acquire US gene specialist Illumina by 15% to $51.00 per share in a bid to speed up the takeover process.

The timing of the Swiss major's decision to raise its bid is a little surprising given that a couple of days ago, Roche extended its original (and rejected) $44.50 per share offer, valuing Illumina at around $5.70 billion, for the second time to April 20. That is two days after Illumina's annual meeting to be held on April 18, where Roche is trying to get its own slate of directors elected to the board.

Last week, Roche chief executive Severin Schwan criticised Illumina's management, saying its "inactivity" in agreeing a deal is hurting the company's shareholders. Now, in a letter to the US firm's CEO, Jay Flatley, Franz Humer, the Basel-headquartered firm's chairman, says that "based on our discussions with Illumina shareholders we have seen interest to accelerate the takeover process".

The higher offer, which values Illumina at around $6.60 billion, represents "a substantial premium of 88%" over its closing stock price on December 21, the day before market rumours about a potential deal emerged. Dr Humer says "it has been and remains Roche’s preference to conclude a negotiated transaction" and "we hope that you will agree that our new price presents a very attractive opportunity".

The letter to Mr Flatley goes on to say that "if you continue to decline to negotiate with us, we will have no choice but to continue our effort to effect a transaction unilaterally". However, Dr Humer concludes, "I strongly hope that you will either agree to commence discussions with us now or remove all obstacles so that your shareholders can make their own determinations about the adequacy of our increased offer".

Illumina responded to the offer by recommending that its stockholders take no action until the board thoroughly reviews Roche’s revised proposal.