Release Details

SOUTH PLAINFIELD, NJ AND CAMBRIDGE, MA – SEPTEMBER 2, 2011 – PTC Therapeutics, Inc. and Genzyme, a Sanofi company, announced today the restructuring of their collaboration. Under the original agreement, PTC held commercial rights for the U.S. and Canada and Genzyme held commercial rights in all other countries. Under the restructured agreement, PTC regains worldwide rights to ataluren and Genzyme retains an option to commercialize ataluren in indications other than nonsense mutation Duchenne/Becker muscular dystrophy (nmDBMD) outside the U.S. and Canada. PTC will continue to conduct worldwide development in all indications with a near-term focus on late-stage programs in nmDBMD and nonsense mutation cystic fibrosis.

"We have been very pleased with our long-standing relationship with PTC," said David Meeker, M.D., Chief Operating Officer, Genzyme. "The decision to restructure this agreement is a result of a recent portfolio assessment, and will enable us to intensify our focus on other areas of development within Genzyme where we believe we have the best ability to develop therapies to benefit the rare disease community. However, our option to reengage the collaboration reflects our belief in the potential of this approach for the treatment of nonsense mutation genetic disorders. While we will no longer be involved in advancing ataluren in nmDBMD, we remain committed to the neuromuscular community."

"PTC and Genzyme share a strong commitment for bringing treatments to patients with rare and life-threatening genetic disorders," said Stuart Peltz, Ph.D., President and Chief Executive Officer, PTC Therapeutics, Inc. "We have benefited greatly from our partnership with Genzyme and we look forward to rapidly advancing the development of ataluren."

ABOUT ATALUREN
An investigational new drug discovered by PTC Therapeutics, ataluren is a protein restoration therapy designed to enable the formation of a functioning protein in patients with genetic disorders caused by a nonsense mutation. A nonsense mutation is an alteration in the genetic code that prematurely halts the synthesis of an essential protein. The resulting disorder is determined by which protein cannot be expressed in its entirety and is no longer functional, such as dystrophin in nmDBMD. The development of ataluren has been supported by grants from Cystic Fibrosis Foundation Therapeutics Inc. (the nonprofit affiliate of the Cystic Fibrosis Foundation); Muscular Dystrophy Association; FDA's Office of Orphan Products Development; National Center for Research Resources; National Heart, Lung, and Blood Institute; and Parent Project Muscular Dystrophy.

ABOUT PTC THERAPEUTICS, INC.
PTC is a biopharmaceutical company focused on the discovery, development and commercialization of orally administered small-molecule drugs that target post-transcriptional control processes. Post-transcriptional control processes regulate the rate and timing of protein production and are of central importance to proper cellular function. PTC's internally discovered pipeline addresses multiple therapeutic areas, including rare genetic disorders, oncology and infectious diseases. PTC has developed proprietary technologies that it applies in its drug discovery activities and has served as the basis for collaborations with leading biopharmaceutical companies. For more information, visit the company's web site at www.ptcbio.com.

ABOUT GENZYME, A SANOFI COMPANY
One of the world's leading biotechnology companies, Genzyme is dedicated to making a major positive impact on the lives of people with serious diseases. Since its founding in 1981, the company has introduced breakthrough treatments that have provided new hope for patients. The company's areas of focus are rare genetic diseases, multiple sclerosis, cardiovascular disease, and endocrinology. Genzyme is a Sanofi company. Genzyme's press releases and other company information are available at www.genzyme.com.

FOR MORE INFORMATION:
Investor and Media

Jane Baj                                     Sheryl Seapy

PTC Therapeutics, Inc.              Pure Communications
(908) 912-9167                           (949) 608-0841
jbaj@ptcbio.com                         sheryl@purecommunicationsinc.com

Media contact:                            Investor contact:
Lori Gorski                                  Kristen Galfetti
Genzyme                                    Sanofi US 
(617) 768-9344                           (617) 768-6563
Lori.gorski@genzyme.com          Kristen.Galfetti@Sanofi.com

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