Question marks are now hanging over Shire Pharmaceuticals’ proposed $1.6 billion dollar takeover of Transkaryotic Therapies after one of the latter firm’s key shareholders said that the price tag did not adequately reflect the US firm’s current value.

In an open letter filed with the US Securities and Exchange Commission, Millenco, which holds 8.8% of TKT’s shares, said that, because of the recent positive data for its Hunter syndrome drug [[21/06/05c]], the firm was worth somewhere between the mid-$40s to the mid-$50s range – significantly more than the $37 per share Shire is offering.

Millenco said it was not faulting the TKT board for accepting the $37 per share offer, but explained “as shareholders, we now have a different decision to make based on significantly more favorable information… We are confident that the TKT stock would be trading well over $37 on a standalone basis in the absence of this transaction.”

The organisation said that it was evaluating all its options, including voting against the merger.

No-one from Shire was available for comment at the time of going to press, but a company spokeswoman told Reuters on Friday that the firm remained confident that the deal would go ahead, and that it represented a good value for both sets of shareholders.