By Greg Roumeliotis

(Reuters) - U.S. biotechnology company Biogen Inc <BIIB.O> has not received any formal expressions of interest from potential acquirers and is not actively soliciting takeover offers, according to a person familiar with the matter.

While some of Biogen's peers have approached individual board directors of the company over time, nothing has been presented to Biogen's board for consideration recently, the person said on Wednesday.

One reason that no formal offer has materialized is that Biogen values its portfolio of neurology drugs highly, and would expect any proposal to come with a significant premium, the person added.

The Wall Street Journal reported on Tuesday, citing sources, that Allergan Plc <AGN.N> and Merck & Co Inc <MRK.N> had sounded out Biogen on the possibility of a takeover. Merck expressed more of an interest in Biogen than Allergan, but this did not result in any offer, the source said.

The source asked not to be identified because Biogen's deliberations are confidential. Biogen, Allergan and Merck offered no comment.

Cambridge, Massachusetts-based Biogen has a market value of $70 billion. The company's $11 billion in annual revenue comes primarily from its multiple sclerosis portfolio, about $4 billion of which may be subject to generic competition in coming years.

Earlier this week, Biogen said it would develop and commercialize an experimental genetic muscle-disorder drug called nusinersen after an interim analysis of late-stage data showed patients experienced statistically significant improvement.

Facing slowing growth of its flagship multiple sclerosis drug Tecfidera, Biogen last year embarked on a sweeping restructuring program to focus on core areas, such as neurology, with high-risk, potentially high-reward experimental treatments for Alzheimer's disease, among others.

Last month, the company's chief executive, George Scangos, announced plans to step down once a successor is named.

Meanwhile, Allergan recently announced the closing of a deal to sell its generics business to Teva Pharmaceutical Industries Ltd <TEVA.TA> for more than $40 billion, providing Allergan with a substantial war chest that could be deployed for acquisitions.

In April, Allergan, which is based in Dublin, Ireland, terminated its planned merger with U.S.-based rival Pfizer Inc <PFE.N> after new U.S. Treasury rules reduced the tax benefits of the deal.

In earnings calls, Merck, based in Kenilworth, New Jersey, has expressed an interest in growing aggressively through deals, calling business development "a top priority." In 2015, it closed an acquisition of Cubist Pharmaceuticals for $9.5 billion.

(Reporting by Greg Roumeliotis in New York; Additional reporting by Carl O'Donnell in New York; Editing by Tom Brown)