Shire Expands Pipeline to Treat Orphan Muscle Diseases Through Collaboration With Acceleron Pharma

Deal Grants Shire Exclusive Ex-North American Rights to Acceleron's Innovative Class of ActRIIB Molecules, Including ACE-031 Currently in Phase 2 Development to Treat Duchenne Muscular Dystrophy

CAMBRIDGE, Massachusetts, September 9, 2010 - Shire plc (LSE: SHP, NASDAQ: SHPGY), the global specialty
biopharmaceutical company, today announced the expansion of its Human Genetic
Therapies pipeline through the exclusive license, in markets outside of North
America, for the activin receptor type IIB (ActRIIB) class of molecules being
developed by Acceleron Pharma Inc., a private biotechnology company based in
Cambridge, Massachusetts. The collaboration will initially investigate
ACE-031, Acceleron's lead ActRIIB drug candidate, currently in a Phase 2a
trial for the treatment of patients with Duchenne Muscular Dystrophy (DMD).
DMD is a fatal orphan muscle disease with no current treatment. ACE-031 and
other ActRIIB molecules have the potential to be used in other muscular and
neuromuscular disorders with high unmet medical need.

Shire and Acceleron will jointly collaborate on a worldwide development
program to advance ACE-031 into a global Phase 2/3 clinical program designed
to demonstrate disease modification in DMD patients. Shire will utilize its
Lexington, Massachusetts manufacturing facility to produce commercial
supplies of the product for both parties. If marketing authorization is
received, Acceleron will commercialize ACE-031 in the U.S. and Canada, and
Shire has the exclusive right to commercialize the therapy in the rest of the
world.

Under the terms of the agreement, Shire will make an upfront payment to
Acceleron of $45 million. Acceleron is eligible to receive additional
development, regulatory and sales milestone payments of up to $165 million
for the successful commercialization of ACE-031 in DMD, up to an additional
$288 million for successful commercialization of other indications and
molecules, and royalties on product sales. Shire will also make a
contribution to global development costs. Shire's 2010 outlook of Non GAAP
earnings trending towards $4.00 per ADS which was recently announced in its
second quarter earnings press release is unchanged.

"This collaboration is an excellent strategic fit to the work that Shire
is already doing on behalf of patients with rare diseases," said Sylvie
Gregoire, President of Shire Human Genetic Therapies. "Working with Acceleron
on the development of ACE-031 for DMD allows us to use our expertise to help
patients suffering from this devastating disease, as well as expand our
pipeline into a new therapeutic area."

"The structure of this collaboration allows Acceleron to retain
commercial rights in North America with the opportunity to build a highly
valuable business while collaborating with an ideal partner for ACE-031,"
said John Knopf, Ph.D., Chief Executive Officer of Acceleron. "Shire's
international presence and their proven leadership and dedicated focus on
orphan diseases forms the basis for successful collaboration to bring
innovative therapies to patients with enormous unmet medical need."

About Duchenne Muscular Dystrophy (DMD)

DMD is a debilitating and fatal genetic disorder characterized by the
progressive loss of muscle strength and function. It primarily affects boys
and occurs in approximately 1 in every 3,500 live male births. DMD is caused
by genetic mutations that result in the absence of dystrophin, a protein
necessary to maintain the structural integrity of muscle fibers. This
condition leads to damage and deterioration of skeletal and cardiac muscles,
which eventually become infiltrated by non-functional scar and fatty tissue.
As a result, patients experience a relentless decline in muscle strength that
impairs their ability to walk, breathe and live independently. Many patients
spend the majority of their lives using wheelchairs and eventually lose upper
body function as well. Few patients survive beyond their late-20s when their
heart and respiratory muscles weaken and eventually fail.

About ACE-031

ACE-031 is an investigational protein therapeutic designed to build
muscle and increase strength by inhibiting signaling through a cell surface
receptor called activin receptor type IIB (ActRIIB). ACE-031 is a recombinant
fusion protein that is produced by joining a portion of the human ActRIIB
receptor to a portion of a human antibody. This creates a freely circulating,
decoy version of ActRIIB which interferes with proteins, such as GDF-8
(myostatin), that normally limit the growth and regeneration of muscle by
binding to and activating endogenous ActRIIB. Recent studies with ACE-031
suggest that blocking signaling through ActRIIB may be a way to increase
muscle mass and improve physical function. In a range of animal models of
muscle disease, including models of muscular dystrophy, and muscle loss
related to corticosteroid treatment, androgen deprivation or advanced age,
ACE-031 increased muscle mass, strength and physical function. Unlike the
mutation specific RNA based therapeutics in clinical development for DMD,
ACE-031 could potentially benefit all patients with DMD, irrespective of the
underlying genetic mutation. Moreover, given its novel mechanism of action,
ACE-031 could be used in combination with many of the therapies currently in
development.

About Shire PLC

Shire's strategic goal is to become the leading specialty
biopharmaceutical company that focuses on meeting the needs of the specialist
physician. Shire focuses its business on attention deficit hyperactivity
disorder (ADHD), human genetic therapies (HGT) and gastrointestinal (GI)
diseases as well as opportunities in other therapeutic areas to the extent
they arise through acquisitions. Shire's in-licensing, merger and acquisition
efforts are focused on products in specialist markets with strong
intellectual property protection and global rights. Shire believes that a
carefully selected and balanced portfolio of products with strategically
aligned and relatively small-scale sales forces will deliver strong results.

For further information on Shire, please visit the Company's website:
www.shire.com

About Acceleron

Acceleron is a privately held biopharmaceutical company committed to
discover, develop, manufacture and commercialize novel biotherapeutics that
modulate the growth of red blood cells, bone, muscle, fat and the vasculature
to treat musculoskeletal, metabolic and cancer-related diseases. Acceleron's
scientific approach takes advantage of its unique insight into the
regenerative powers of the TGF-β superfamily of proteins. Acceleron utilizes
proven biotherapeutic technologies and capitalizes on the company's internal
GMP manufacturing capability to rapidly and efficiently advance its
therapeutic programs. The investors in Acceleron include Advanced Technology
Ventures, Alkermes, Bessemer Ventures, Celgene, Flagship Ventures, MPM
BioEquities, OrbiMed Advisors, Polaris Ventures, QVT Financial, Sutter Hill
Ventures and Venrock.

For further information on Acceleron Pharma, please visit
www.acceleronpharma.com

"SAFE HARBOR" STATEMENT UNDER THE PRIVATE SECURITIES LITIGATION REFORM
ACT OF 1995

Statements included herein that are not historical facts are
forward-looking statements. Such forward-looking statements involve a number
of risks and uncertainties and are subject to change at any time. In the
event such risks or uncertainties materialize, the Company's results could be
materially adversely affected. The risks and uncertainties include, but are
not limited to, risks associated with: the inherent uncertainty of research,
development, approval, reimbursement, manufacturing and commercialization of
the Company's Specialty Pharmaceutical and Human Genetic Therapies products,
as well as the ability to secure and integrate new products for
commercialization and/or development; government regulation of the Company's
products; the Company's ability to manufacture its products in sufficient
quantities to meet demand; the impact of competitive therapies on the
Company's products; the Company's ability to register, maintain and enforce
patents and other intellectual property rights relating to its products; the
Company's ability to obtain and maintain government and other third-party
reimbursement for its products; and other risks and uncertainties detailed
from time to time in the Company's filings with the Securities and Exchange
Commission.

    For further information please contact:

    Investor Relations
    Eric Rojas
    +1-781-482-0999

    Media

    Jessica Mann (Rest of the World)
    +44-1256-894-280

    Jessica Cotrone (North America, HGT)
    +1-781-482-9538

For further information please contact: Investor Relations, Eric Rojas, +1-781-482-0999; Media, Jessica Mann (Rest of the World), +44-1256-894-280; Jessica Cotrone (North America, HGT)+1-781-482-9538