For Immediate Release

PTC THERAPEUTICS RAISES $35 MILLION AND APPOINTS TWO NEW BOARD MEMBERS

Wednesday, January 7, 2003

South Plainfield, NJ, -- PTC Therapeutics, Inc. (PTC), a privately held biopharmaceutical company applying its integrated RNA biology and chemistry platforms to discover and develop small molecule drugs, announced today that it has raised $35 million through a private placement of Series E Preferred Stock. CSFB Private Equity and HBM Bioventures led this round of financing with a strong syndicate of new and existing investors, including: Bay City Capital, Delphi Ventures, Hansa Special Opportunities Fund Limited, HealthCap, Novartis BioVentures, Novo A/S, POSCO BioVentures, and Vulcan Capital.

Commenting on this financial milestone, Stuart Peltz, Ph.D., President and CEO of PTC, said, "Completing this round of financing with such experienced and prominent investors further validates PTC's approach and accomplishments to date. We are privileged to be well capitalized and believe the support of new and existing investors is a result of our track record of delivering on scientific and corporate milestones."

"The proceeds of this round will support the clinical development of PTC124, which is on track for an IND submission in the second quarter of 2004, as well the continued advancement of several programs currently in lead optimization. We continue to make significant progress in advancing our preclinical drug candidates particularly in the oncology and antiviral areas, where programs have advanced very rapidly to late stage optimization with excellent activity in preclinical disease models," added Dr. Peltz.

"We believe that the regulation of gene expression through post- transcriptional control mechanisms is a promising area of drug discovery. PTC has defined and explored this new area of biology and quickly developed unique programs in multiple therapeutic areas," said Michael Schmertzler of CSFB Private Equity. "PTC's robust and diversified pipeline is the result of hard work from the Company's experienced scientists and the execution of a sound business strategy by a dedicated management team. We are confident that PTC will be an important innovator in the discovery and development of small molecule drugs that will greatly improve the quality of life for people suffering from a broad range of diseases. We have been impressed by the Company's commitment and accomplishments, and we are proud to support PTC in this new and exciting phase," he added.

The company also announced that Axel Bolte of HBM Partners and Michael Kranda of Vulcan Inc. have joined the Board of Directors effective immediately.

Axel Bolte is an investment advisor and member of the management team of HBM Partners, based in Zurich, Switzerland. He joined HBM Partners from NMT New Medical Technologies, the first Swiss Venture Capital group focused exclusively on the life sciences. Previously, Mr. Bolte was with Serono SA, where he held a position in R&D management. Mr. Bolte holds an MBA from the University of St. Gallen (HSG) and studied biochemistry at the Swiss Federal Institute of Technology (ETHZ) and at the University of Cambridge, UK.

Michael Kranda is Director of Biotechnology Venture Investments of Vulcan Capital. Mr. Kranda was CEO of Oxford Glycosciences, a British biotech company; president and chief operating officer of Immunex; and former chief of staff to King County Prosecutor Norm Maleng. He holds an MBA from the University of Washington.

"We are excited to have both Mr. Bolte and Mr. Kranda join our Board of Directors. Their collective experience spans the biotechnology, pharmaceutical and financial industries. We expect PTC to benefit significantly from their business insight and corporate development knowledge," said Dr. Peltz.

About PTC124

PTC124 is the development candidate selected in PTC's Genetic Disorders program. In this program, PTC has identified several classes of molecules that can overcome a type of genetic alteration known as a nonsense mutation. Nonsense mutations disrupt the process of protein synthesis, resulting in the production of incomplete proteins, and cause disease in a significant percentage of patients with genetic disorders (for example, approximately 15% of the cases of Duchenne muscular dystrophy and 10% of cases of cystic fibrosis are due to nonsense mutations). In preclinical testing of PTC124 in models of genetic disorders the compound has been effective, well tolerated, and orally bioavailable. Indications that may be pursued include Duchenne muscular dystrophy, cystic fibrosis, lysosomal storage disorders, and hemophilia.

About PTC Therapeutics

PTC Therapeutics, Inc. discovers and develops small molecule drugs by applying its expertise in RNA biology to modulate gene expression. This approach has advanced PTC's programs rapidly from targets to preclinical drug candidates. PTC's pipeline includes programs in genetic disorders, oncology and infectious diseases. PTC is located in NJ's pharmaceutical corridor (South Plainfield) and employs 92 professionals with extensive experience in the biopharmaceutical industry.

About the Investors: Bay City Capital

Bay City Capital is a San Francisco-based private merchant bank that focuses exclusively on the life sciences industry, including the pharmaceutical, biomedical, life sciences information technology, and nutrition and agribusiness sectors. BCC provides investment capital and strategic and transaction advisory services to publicly traded and privately held companies. Since inception in 1997, the firm has committed over $450 million across four investment funds, BCC Funds I, II, and III and the North American Nutrition and Agribusiness Fund, with plans to expand its funds continuously over time. More information about Bay City Capital can be found at http://www.baycitycapital.com/.

CSFB Private Equity

CSFB Private Equity, the global private equity arm of Credit Suisse First Boston, is one of the largest managers of alternative assets in the world, with over $31 billion in funds under management. CSFB Private Equity is comprised of investment funds that focus on domestic and international leveraged buyouts and other private equity investments, including mezzanine, real estate, venture capital and investments in other funds. CSFB Private Equity includes the family of DLJ Merchant Banking funds. CSFB Private Equity maintains offices in New York, London, Buenos Aires, Chicago, Hong Kong, Los Angeles, Menlo Park, San Francisco, São Paulo and Tokyo. More information about CSFB Private Equity can be found at http://www.csfb.com/private_equity.

Delphi Ventures

Delphi Ventures is a private venture capital firm providing equity financing and supportive business expertise to young biomedical and healthcare companies. Our goal is to contribute added value to the companies we fund by serving as active investors. Since our formation in 1988 Delphi has invested in over 100 companies encompassing every segment of the biomedical field including: Biopharmaceuticals/Drug Discovery Tool, Medical Devices and Diagnostics and Healthcare Services. More information about Delphi Ventures can be found at http://www.delphiventures.com/.

Hansa Special Opportunities Fund Limited

A Bermuda based open-ended investment fund specializing in unquoted investments where intellectual property is a key driver of value.

HBM Bioventures

HBM Bioventures is one of Europe's largest investors in biotechnology, emerging pharma and medical technology with a capitalization of approximately USD 650 million. The fund invests globally in mid to late stage private companies, as well as in selected small cap publicly quoted companies. HBM Bioventures is advised by HBM Partners, based in Zurich, Switzerland. The team of HBM Partners consists of 16 investment professionals with extensive experience in the pharmaceutical industry as well as in private equity. More information about HBM Bioventures can be found at http://www.hbmbioventures.com/.

HealthCap

With a committed capital of approximately $750 million, HealthCap is the largest specialized provider of venture capital within life sciences in the Nordic countries and one of the largest independent actors in the sector in Europe. HealthCap invests in early stage opportunities as well as more mature companies on a global basis. More information about HealthCap can be found at http://www.healthcap.se/.

Novartis BioVenture Fund

The objective of the BioVenture Fund, a sub-fund of the Novartis Venture Fund family, is to generate long-term capital gains for both entrepreneurs and investors. The Fund invests in product-focused biotech, pharmaceutical and healthcare companies at all stages, with an emphasis on the United States. Initial or follow-on investments range from USD 0.5 to 5 million. More information about Novartis BioVenture Fund can be found at http://www.venturefund.novartis.com/.

Novo A/S

Novo A/S is a private company, wholly owned by the Novo Nordisk Foundation. Novo A/S provides venture capital and expertise for development stage companies with a pioneering concept within life-sciences. Novo A/S has a rapidly expanding portfolio of venture capital investments. Furthermore, Novo A/S holds significant share holdings in Novo Nordisk A/S and Novozymes A/S. More information about Novo A/S can be found at http://www.novo.dk/.

POSCO BioVentures

POSCO BioVentures is a venture capital fund dedicated solely to biotechnology investments. POSCO BioVentures has only one limited partner, POSCO, the $11 billion Korean steel giant. POSCO BioVentures will invest with POSCO's strategic interests in mind, helping to establish POSCO's reputation and build its presence in the biotechnology space. POSCO BioVentures Fund I, L.P. has $50 million under management. More information about POSCO BioVentures can be found at http://www.poscobioventures.com/.

VULCAN CAPITAL

Vulcan Capital is the private investment arm of Vulcan Inc., the project and investment management company founded by Paul G. Allen in 1986 to manage his personal and business initiatives. Focused on generating long-term value appreciation across a diversified, multi-billion dollar portfolio, Vulcan Capital spans various industry sectors and investment classes - from early stage venture investments and public equity investing to leveraged buyouts and acquisitions. The portfolio's key holdings include Charter Communications, DreamWorks SKG, Digeo Broadband and Oxygen Media, among others. Learn more about Vulcan Capital online at http://www.vulcan.com/.

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