Genzyme Begins Phase 2 Trial of Oral Treatment for Gaucher Disease

July 26, 2006, Genzyme Corporation (Nasdaq: GENZ) today announced that it has begun to treat patients in a Phase 2 clinical trial of Genz-112638, an oral therapy being developed for the treatment of Gaucher disease. Genzyme will conduct the study in patients with Type 1 Gaucher disease at medical centers in Europe, Israel, South America and the United States.

Initiation of this trial reflects Genzyme’s strong commitment to developing a next-generation therapy for patients with Gaucher disease that has the potential to decrease or eliminate their need for enzyme replacement therapy, the current standard of care.

“We are proud to advance our small molecule program into Phase 2 testing, which will help enable us to determine the potential of this therapy to have a meaningful impact on the lives of patients with Gaucher disease,” said Rich Moscicki, MD, chief medical officer, Genzyme. “We remain committed to continued innovation on behalf of people with Gaucher disease, through our efforts to develop new treatment approaches and to further improve upon the care patients receive with enzyme replacement therapy.”

Genz-112638, a ceramide analog given as an oral capsule, is designed to inhibit the enzyme glucosylceramide synthase, which results in reduced production of glucocerebroside. This 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 addition to Gaucher disease, there are a variety of other conditions that can be caused by malfunctions in the pathway targeted by this molecule, such as Tay-Sachs, Sandhoff, and Fabry diseases.

The open-label trial will evaluate patient response for one year according to several primary endpoints, including changes in hemoglobin, platelet levels and spleen volume. Other endpoints to be investigated include change in liver volume and a series of biomarkers and quality of life indicators relevant to Gaucher disease.

Initiation of the Phase 2 program follows completion of an extensive pre-clinical research effort and a Phase 1 program that involved more than 120 subjects in three separate studies. The first public presentation of the Genz-112638 pre-clinical and Phase 1 data occurred July 19 at the European Working Group on Gaucher Disease Workshop in Cambridge, UK.

Genzyme’s Commitment to Gaucher Disease

Development of Genz-112638 reflects Genzyme’s long-standing commitment to improving the care of patients with Gaucher disease. Since introducing enzyme replacement therapy more than 15 years ago, Genzyme has engaged in extensive basic science research to further improve its safety and effectiveness. Post-approval clinical trials have helped to demonstrate the impact enzyme replacement therapy can have on different manifestations of the disease, such as bone involvement. Management of the Gaucher Registry, the largest database of its kind, has yielded insights that have shaped how physicians and their patients manage Gaucher disease. Genzyme has also performed extensive research into gene therapy for single gene disorders like Gaucher disease.

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. This year marks the 25th anniversary of Genzyme’s founding. Since 1981, the company has grown from a small start-up to a diversified enterprise with more than 8,500 employees in locations spanning the globe and 2005 revenues of $2.7 billion. Genzyme has been selected by FORTUNE as one of the “100 Best Companies to Work for” in the United States.

With many established products and services helping patients in more than 80 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 diseases, and diagnostic testing. Genzyme’s commitment to innovation continues today with a substantial development program focused on these fields, as well as heart disease and other areas of unmet medical need.

This press release contains forward-looking statements, including statements regarding clinical trial plans for GENZ-112638; potential indications for GENZ-112638, including Gaucher disease; and expectations regarding the potency and specificity of GENZ-112638. These statements are subject to risks and uncertainties that could cause actual results to differ materially from those forecast in these forward-looking statements. These risks and uncertainties include, among others, the results and timing of preclinical and clinical studies of GENZ-112638 for Gaucher disease and other potential indications; the enrollment rate for the Phase 2 trial of GENZ-112638; Genzyme’s ability to obtain regulatory approvals and the timing of receipt of such approvals; 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 “Factors Affecting Future Operating Results” in Genzyme’s Quarterly Report on Form 10-Q for the quarter ended March 31, 2006. 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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