PTC Therapeutics, Inc. recently announced results from the Phase 3, double-blind, placebo-controlled, 48-week ACT DMD trial of TranslarnaTM (ataluren), an oral, first-in-class, protein restoration therapy for the treatment of nonsense mutation Duchenne muscular dystrophy (nmDMD). The trial results showed clinically meaningful benefits for Translarna-treated patients. In the overall intent-to-treat study population, the primary endpoint of change from baseline in the 6-minute walk test (6MWT) demonstrated a 15 meter benefit (p=0.213), which was not statistically significant. A highly significant benefit of 47 meters (p=0.007) was demonstrated in the pre-specified patient population of 300-400 meters at baseline as measured by the 6MWT, which is in line with the Company’s prior experience in its Phase 2b trial and consistent with the evolving understanding of the 6MWT. Importantly, no patients in this group lost ambulation (0/47) versus four patients in the placebo group (4/52). Translarna showed a benefit over placebo across key secondary and tertiary endpoints, including timed function tests (10 meter Run/Walk, 4 Stair Climb, 4 Stair Descend) and the North Star Ambulatory Assessment test. In addition, a pre-specified meta-analysis of the combined placebo-controlled ACT DMD and Phase 2b trials demonstrated a statistically significant benefit of Translarna across the primary (p=0.015) and key secondary endpoints.

“These results show Translarna’s ability to change the course of DMD disease progression. The totality of the data from our two robust placebo-controlled studies across over 400 patients demonstrate a clinically relevant impact on patients’ lives,” said Stuart W. Peltz, Ph.D., chief executive officer of PTC Therapeutics. “We plan to submit these results to the EMA and complete our NDA submission to the FDA by the end of the year. We sincerely thank all the boys and young men, their parents, and the investigators who participated in this study for their commitment.”

After the completion of ACT DMD, both placebo and treated patients were given the opportunity to continue on Translarna in an open-label extension study. Ninety-seven percent of the patients who completed ACT DMD enrolled in the extension study.

“These important results demonstrate positive treatment effects across multiple endpoints and validate our emerging understanding of the optimal patient group in which to demonstrate benefit in the 6-minute walk test. It is particularly impressive that these results were observed in a one-year study,” said Craig M. McDonald, M.D., an investigator of ACT DMD and professor of Pediatrics and chair of the Department of Physical Medicine and Rehabilitation at the University of California Davis School of Medicine. “It is compelling to see the consistency of clinical data for Translarna in another large, placebo-controlled study. The evidence demonstrates a clinically meaningful benefit for nmDMD patients.”

ACT DMD, the largest placebo-controlled study ever conducted in patients with DMD, is a multi-center, randomized, double-blind, Phase 3 clinical trial involving 228 patients in 53 sites across 18 countries. Patients between the ages of 7 and 16 with nmDMD were randomized to receive either Translarna 40mg/kg per day (n=114) or placebo (n=114) over 48 weeks. The primary endpoint was change from baseline in the 6MWT. Analyses of data from pre-specified subgroups, including the pre-specified subgroup of patients with baseline 6-minute walk distance (6MWD) of 300 – 400 meters, were also completed. Key secondary outcome measures were timed-function tests, including time to run or walk 10 meters and the time to ascend or descend four stairs. Tertiary endpoints included the North Star Ambulatory Assessment test, a functional

scale designed for ambulant boys affected by DMD, and the Pediatric Outcomes Data Collection Instrument (PODCI), a validated tool for measuring quality of life in pediatric patients with orthopedic conditions. Supportive analyses of ambulation were conducted, including the proportion of patients with at least 10% worsening in 6MWD. A pre-specified meta-analysis of combined data from the ACT DMD and Phase 2b (ambulatory decline phase) studies was also performed.

“Duchenne muscular dystrophy is a devastating, progressive muscle-wasting disease, which cuts short the lives of boys and young men,” said Pat Furlong, President, Parent Project Muscular Dystrophy. “We are excited by the results from PTC’s study and appreciate the perseverance it took to achieve this important milestone. Having treatments available that can maintain muscle function and improve quality of life are vitally important to patients and their families. We look forward to the FDA’s review of these data.”

The ACT DMD study confirmed the favorable safety profile of Translarna, which was generally well-tolerated, consistent with results from previous studies. More than 500 nmDMD patients have now received Translarna, the largest population to be treated with a disease-modifying agent in DMD.

Translarna received marketing authorization from the European Medicines Agency (EMA) in 2014 for use in ambulatory nmDMD patients who are five years of age and older. PTC intends to submit the results from the ACT DMD study to the EMA and to complete its rolling submission for a New Drug Application (NDA) to the FDA by the end of 2015.

About Duchenne Muscular Dystrophy

Primarily affecting males, Duchenne muscular dystrophy (DMD) is a progressive muscle disorder caused by the lack of functional dystrophin protein. Dystrophin is critical to the structural stability of skeletal, diaphragm, and heart muscles. Patients with DMD, the more severe form of the disorder, lose the ability to walk as early as age 10 and experience life- threatening lung and heart complications in their late teens and twenties. More information about DMD is available through the Muscular Dystrophy Association (www.mdausa.org), Parent Project Muscular Dystrophy (www.parentprojectmd.org), Action Duchenne

(www.actionduchenne.org), United Parent Projects Muscular Dystrophy (uppmd.org), Muscular Dystrophy Campaign (www.muscular-dystrophy.org) and AFM (l’Association francaise contre les myopathies), (www.afm-telethon.fr).

About Translarna

Translarna, discovered and developed by PTC Therapeutics, Inc., 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 Duchenne muscular dystrophy. Translarna is licensed in the European Economic Area for the treatment of nonsense mutation Duchenne muscular dystrophy in ambulatory patients aged five years and older. Translarna is an investigational new drug in the United States. The development of Translarna 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.

The FDA and the European Commission have granted Translarna Orphan Drug status for the following indications: Duchenne muscular dystrophy, cystic fibrosis, Mucopolysaccharidosis I (MPS 1), and aniridia.

About PTC Therapeutics

PTC is a global biopharmaceutical company focused on the discovery, development, and commercialization of orally administered, proprietary small molecule drugs targeting an area of RNA biology we refer to as post-transcriptional control. Post-transcriptional control processes are the regulatory events that occur in cells during and after a messenger RNA, or mRNA, molecule is copied from DNA through the transcription process. PTC’s internally discovered pipeline addresses multiple therapeutic areas, including rare disorders, oncology, and infectious diseases. PTC has discovered all of its compounds currently under development using its proprietary technologies. PTC plans to continue to develop these compounds both on its own and

through selective collaboration arrangements with leading pharmaceutical and biotechnology companies. For more information on the company, please visit our website www.ptcbio.com