First Patient Enrolled in Phase 3 Trials of Genzyme Oral Capsule for Gaucher Disease

Date: October 20, 2009

Genzyme Corporation (NASDAQ: GENZ) today announced that the company has begun enrollment in the first of two global, multi-center, phase 3 trials of Genz-112638, a potential new oral therapy for Gaucher disease type 1. The two multi-national, multi-center trials are being conducted to evaluate the safety and efficacy of the small molecule.

The first trial, known as ENCORE, has enrolled its first patient. ENCORE is a randomized, open-label study for adult patients with Gaucher disease type 1 designed to compare Genz-112638 to Cerezyme® (imiglucerase for injection). Adult patients who have previously received Cerezyme for at least three years and have reached their therapeutic goals may qualify for this trial. Genzyme expects to enroll nearly 200 patients in the ENCORE trial, with a treatment duration of one year.

The ENGAGE trial is a randomized, double-blind, placebo-controlled study for patients with a confirmed diagnosis of Gaucher disease type 1. Patients with intact spleens who have not been treated in the last 12 months for Gaucher disease may qualify for this study. Genzyme expects to enroll 36 patients in the ENGAGE trial, with a treatment duration of nine months.

Currently over 35 centers in more than 20 countries are participating in these trials. Genzyme expects that the number of recruiting centers will expand, as more sites receive regulatory approval to proceed. At the conclusion of both trials, patients will be offered the option of continuing on therapy with Genz-112638 as part of the extension phase of the program.

“We remain very enthusiastic about this potential new therapy for Gaucher disease, which could offer flexibility and choice to patients and to physicians,” said Genzyme Senior Vice President Geoff McDonough, M.D. “Our studies to date for Genz-112638 suggest a potent and highly-specific therapy that was well-tolerated and that we believe could impact patients in a meaningful, positive way.”

To learn more about these trials for Genz-112638, contact Genzyme Medical Information at medinfo@genzyme.com or 1-800-745-4447. More information can also be found at www.clinicaltrials.gov.

About Genz-112638

Genz-112638, a novel glucosylceramide analog given orally, is designed to partially inhibit the enzyme glucosylceramide synthase, which results in reduced production of glucosylceramide. Glucosylceramide is the substance that builds up in the cells and tissues of people with Gaucher disease. In preclinical studies, the molecule has shown high potency and specificity. In February, Genzyme reported that the phase 2 clinical trial of Genz-112638 met its composite primary efficacy endpoint: a clinically meaningful response in at least two of three endpoints (improvements in spleen size, hemoglobin and platelet levels) in individual patients after the 52-week study period. The safety analysis for the phase 2 trial demonstrated that Genz-112638 was well tolerated. Related adverse events in the phase 2 study included infrequent abdominal discomfort and diarrhea, as well as transient palpitations and headache. Patients continue to be treated in the extension phase of the study and have now completed two years of treatment.

Based on its mechanism of action, which is independent of genotype, Genz-112638 is a potential therapy for all adult patients with Gaucher disease type 1. The compound was developed with James A. Shayman, M.D. from the University of Michigan.

About Genzyme

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 1981, the company has grown from a small start-up to a diversified enterprise with more than 11,000 employees in locations spanning the globe and 2008 revenues of $4.6 billion. In 2007, Genzyme was chosen to receive the National Medal of Technology, the highest honor awarded by the President of the United States for technological innovation.

With many established products and services helping patients in 100 countries, Genzyme is a leader in the effort to develop and apply the most advanced technologies in the life sciences. The company's products and services are focused on rare inherited disorders, kidney disease, orthopaedics, cancer, transplant and immune disease, and diagnostic testing. Genzyme's commitment to innovation continues today with a substantial development program focused on these fields, as well as cardiovascular disease, neurodegenerative diseases, and other areas of unmet medical need.

This press release contains forward-looking statements regarding Genzyme’s clinical development plan for Genz-112638 as a potential investigational therapy for Gaucher disease, including that it expects to fully enroll its Phase 3 clinical studies for Genz- 112638, expects to expand its recruiting capacity; and believes Genz-112638 could offer flexibility and choice to patients and physicians and could be a potent, highly specific and well tolerated therapy that could impact patients in a positive and meaningful way. These statements are subject to risks and uncertainties that could cause actual results to differ materially from those forecasted. These risks and uncertainties include, among others: Genzyme’s ability to pursue its Phase 3 studies expeditiously and in a broad group of Gaucher type I patients, Genzyme’s ability to develop Genz-112638 into a meaningful treatment option for Gaucher type I patients, and the risks and uncertainties described in Genzyme's SEC reports filed under the Securities Exchange Act of 1934, including the factors discussed under the caption "Risk Factors" in Genzyme's Quarterly Report on Form 10Q for the second quarter of 2009. Genzyme cautions investors not to place substantial reliance on the forward-looking statements contained in this press release. These statements speak only as of today’s date and Genzyme undertakes no obligation to update or revise the statements.

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