FDA Provides Clarity to Isis Regarding the Development Path for Mipomersen

Isis Pharmaceuticals, Inc. (Nasdaq: ISIS) and Genzyme Corp. (Nasdaq: GENZ) announced today that the FDA has provided guidance regarding approval requirements for mipomersen. The FDA has indicated that reduction of LDL-cholesterol is an acceptable surrogate endpoint for accelerated approval of mipomersen for use in patients with homozygous familial hypercholesterolemia (hoFH). The FDA will require data from two ongoing preclinical studies for carcinogenicity to be included in the hoFH filing, which is now anticipated to take place in 2010. A phase 3 study of mipomersen in hoFH is currently enrolling patients.

The companies plan to conduct an outcome trial to support full approval of mipomersen for hoFH and to expand its indication to include other patients with high cholesterol who are at high risk for cardiovascular events. In response to the FDA’s guidance, the companies are revising the development plan for mipomersen to accelerate plans for an outcome study. Isis and Genzyme plan to communicate further details of the revised development plan as they are finalized.

“Because our development plan, and our joint plan with Genzyme, has always included outcome studies to maximize the profile and commercial potential of mipomersen, this FDA guidance accelerates these planned studies and simplifies the overall development path for mipomersen,” said Dr Stan Crooke, Chairman and Chief Executive Officer of Isis. “Conducting an outcome study in parallel with our continued evaluation of the effects of mipomersen on atherogenic lipids will allow us to submit a much stronger NDA for high risk patients. We are confident that mipomersen will bring benefit to patients with high cholesterol and remain committed to its development and commercialization.”

“We are pleased that the FDA has given clear direction on what will be required for the approval of mipomersen, and has acknowledged its potential to help high risk patients whose needs are not being met by current therapies,” said Henri A. Termeer, Genzyme’s chairman and chief executive officer. “Having outcome data earlier on in the development process will be important to patients and serve to enhance the value of this treatment. We plan to engage in discussions with regulatory agencies in Europe and the rest of the world, and look forward to receiving their feedback.”
Isis Safe Harbor Statement

This press release includes forward-looking statements regarding the development, activity, therapeutic potential and safety of mipomersen in treating patients with high cholesterol. Any statement describing Isis’ goals, expectations, financial or other projections, intentions or beliefs is a forward-looking statement and should be considered an at-risk statement, including those statements that are described as Isis’ goals. Such statements are subject to certain risks and uncertainties, particularly those inherent in the process of discovering, developing and commercializing drugs that are safe and effective for use as human therapeutics, and in the endeavor of building a business around such products. Isis’ forward-looking statements also involve assumptions that, if they never materialize or prove correct, could cause its results to differ materially from those expressed or implied by such forward-looking statements. Although Isis’ forward-looking statements reflect the good faith judgment of its management, these statements are based only on facts and factors currently known by Isis. As a result, you are cautioned not to rely on these forward-looking statements. These and other risks concerning Isis’ programs are described in additional detail in Isis’ annual report on Form 10-K for the year ended December 31, 2007, which is on file with the SEC. Copies of this and other documents are available from the Company.

Isis Pharmaceuticals is a registered trademark of Isis Pharmaceuticals, Inc. Ibis Biosciences and Ibis T5000 are trademarks of Ibis Biosciences, Inc. Regulus Therapeutics is a trademark of Regulus Therapeutics LLC.

Genzyme Safe Harbor Statement

This press release contains forward-looking statements, including without limitation, statements concerning mipomersen’s benefits for patients with high cholesterol, the development plan for mipomersen and FDA’s requirements for its approval. 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: the timing of further discussions with FDA regarding the approval of mipomersen; the timing and content of submissions to and decisions made by the FDA relating to mipomersen; further analysis of clinical trial data; the results of other studies; the actual efficacy and safety of mipomersen; 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 2007 Annual Report on Form 10K. 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.

Genzyme® is a registered trademark of Genzyme Corporation. All rights reserved.