For Immediate Release

PTC THERAPEUTICS CLOSES $50 MILLION SERIES E PRIVATE PLACEMENT FINANCING

Wednesday, June 24, 2004

SOUTH PLAINFIELD, NJ -- PTC Therapeutics, Inc., a privately held biopharmaceutical company developing small molecule drugs targeting post-transcriptional mechanisms, announced today the closing of a $50 million private placement. PTC initially raised $35 million in December 2003. This announcement marks the completion of the $50 million financing round. This financing was led by CSFB Private Equity and HBM BioVentures, with participation from existing investors that included Bay City Capital, Delphi Ventures, Hansa Special Opportunities Fund Limited, HealthCap, Novo A/S, and Vulcan Capital. New investors participating in this round of financing included Genavent Partners LP, Novartis BioVentures, and POSCO BioVentures.

"We are extremely proud to have completed the additional financing. This success is a reflection of our track record in executing on our scientific and corporate milestones," commented Stuart Peltz, Ph.D., President and CEO of PTC Therapeutics. "The proceeds of this round of financing will be applied to the clinical development of PTC124, our development candidate in the genetic disorders program, as well as the continued advancement of our and anti-angiogenesis programs, which remain on track to sustain our identification of one development candidate per year."

"We are impressed with PTC's accomplishments to date," said Deepa Pakianathan, Ph.D., of Delphi Ventures. "PTC has a developed a novel approach to drug development utilizing their expertise and understanding of post-transcriptional control mechanisms that is delivering measurable results towards clinical development. The Company's ability to advance multiple programs across several therapeutic areas is a statement to the caliber of the science and excellence of management."

About PTC Therapeutics:

PTC Therapeutics, Inc. discovers and develops small molecule drugs by applying its integrated RNA biology and chemistry platforms. PTC's compounds alter gene expression by selectively modulating how RNA is used to produce proteins. This approach has advanced the Company's drug discovery programs rapidly from targets to preclinical drug candidates. PTC's pipeline includes programs in genetic disorders, oncology and infectious diseases.

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