CAMBRIDGE, MA—Genzyme Corp. (Nasdaq: GENZ) announced today that the European Medicines Agency (EMEA) has accepted its marketing authorization application for Myozyme® (alglucosidase alfa), an investigational enzyme replacement therapy for Pompe disease. If approved, Myozyme would become the first treatment available to patients with Pompe disease, a debilitating and often fatal muscle disorder resulting from an inherited enzyme deficiency.

The EMEA’s Committee for Human Medicinal Products is expected to issue an opinion on the Myozyme application within one year, and a decision by the European Commission is anticipated early in 2006.

“Pompe disease takes a devastating toll on patients and their families,” said Henri A. Termeer, chairman and chief executive officer of Genzyme. “We have proceeded with a great sense of urgency to develop a product that we hope and believe will finally give them a chance. We are enormously grateful to everyone who has contributed so much to get us to this point, and we are working diligently to begin the approval process for Myozyme in other parts of the world next year.”

Myozyme has received orphan medicinal product designation, which applies to treatments for diseases that affect fewer than 5 in 10,000 people in the European Union. Approved orphan medicinal products are granted market exclusivity for 10 years.

Genzyme is seeking approval for Myozyme’s use as a long-term enzyme replacement therapy for all patients with a confirmed diagnosis of Pompe disease, defined as alpha-glucosidase deficiency. Genzyme’s marketing application for Myozyme contains results from several clinical trials, including interim data from the ongoing study AGLU-01702, which is evaluating the use of Myozyme in severely affected children between 6 months and 3 years of age. One-year results from AGLU-01702 will become available during the application-review process, as will interim data from the ongoing study AGLU-01602, which is fully enrolled and includes children younger than 6 months of age with the classical infantile-onset form of Pompe disease.

Nearly 100 Pompe patients are currently receiving Myozyme in clinical studies, through Genzyme’s expanded access program, or through pre-approval access mechanisms sponsored by governments in several European countries.

“This is a very hopeful moment for people with Pompe disease in Europe,” said Ria Broekgaarden, of the Dutch Pompe patient organization VSN (Vereniging Spierziekten Nederland) and secretary of the International Pompe Association. “Patients urgently need treatment, and we will continue to advocate on their behalf.”

Genzyme anticipates submitting a marketing application for Myozyme in the United States in the middle of 2005. Applications in Japan and other countries will follow the U.S. submission. The company continues to make a significant investment in the development of Myozyme, which is its largest research and development project. Genzyme is currently conducting an observational study for patients with the late-onset form of Pompe disease and plans to initiate a placebo-controlled treatment study for late-onset patients next year. The company has also established a registry designed to improve knowledge about Pompe disease by documenting the natural course of the disease, disease management approaches and clinical outcomes. All patients are eligible to participate in the registry through their treating physicians. Genzyme is also engaged in a substantial expansion of manufacturing capacity for Myozyme at its facilities in both the United States and Europe.

About Pompe disease

Pompe disease is an inherited muscle disease that affects fewer than 10,000 people worldwide. The disease is caused by a deficiency of an enzyme known as acid alpha-glucosidase. This deficiency leads to the excessive accumulation of glycogen in the body, particularly in the muscles. Pompe disease manifests as a broad spectrum of clinical symptoms with varying rates of disease progression. Infantile-onset patients present in the first months of life with an enlarged heart and skeletal and respiratory muscle weakness, and most die from cardiac or respiratory complications by one year of age. Late-onset patients may present with muscle or respiratory weakness anytime during childhood or adulthood, and disease progression is less rapid. Late-onset patients often require mechanical ventilation for breathing assistance and mobility aids such as canes, walkers or wheelchairs. Late-onset patients will experience a shortened lifespan due to progressive respiratory failure. Pompe disease belongs to a family of approximately 40 rare inherited diseases known as lysosomal storage disorders.

About Genzyme

Genzyme Corporation is a global biotechnology company dedicated to making a major positive impact on the lives of people with serious diseases. The company’s broad product portfolio is focused on rare genetic disorders, renal disease, osteoarthritis and immune-mediated diseases, and includes an industry-leading array of diagnostic products and services, and sophisticated biomaterials. Genzyme’s commitment to innovation continues today with research into novel approaches to cancer, heart disease, and other areas of unmet medical need. Approximately 7,000 Genzyme employees in offices around the globe serve patients in more than 80 countries.

Safe-Harbor Statement

This press release contains forward-looking statements, including statements about: the potential receipt of marketing approval for Myozyme in Europe; regulatory plans and expected timelines, including without limitation the expected timing of an opinion from the Committee for Human Medicinal Products and a decision from the European Commission; the expected timing of regulatory submissions in the United States, Japan and other countries; clinical trial plans; and estimates concerning the Pompe patient population. These statements are subject to risks and uncertainties that could cause actual results to differ materially from those projected in these forward-looking statements. These risks and uncertainties include, among others: the actual timing and content of submissions to and decisions made by the Committee for Human Medicinal Products, the European Commission and other regulatory authorities regarding marketing authorization applications for Myozyme and the labeling for Myozyme; the actual timing and results of clinical trials of Myozyme; the ability to manufacture sufficient quantities of product for development and commercialization activities and to do so in a timely and cost efficient manner; the accuracy of the company’s information about the Pompe patient population; and the risks and uncertainties described in reports filed by Genzyme with the Securities and Exchange Commission. Please see the disclosure under the heading “Factors Affecting Future Operating Results” in the Management’s Discussion and Analysis of Financial Condition and Results of Operations section of Genzyme’s Quarterly Report on Form 10-Q for the quarter ended September 30, 2004 for a more complete discussion of these and other risks. Genzyme cautions investors not to place substantial reliance on the forward-looking statements contained in this press release. These statements speak only as of the date of this press release, and Genzyme undertakes no obligation to update or revise the statements.

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