Transkaryotic Therapies Inc announced The Technical Board of Appeals of the European Patent Office ("EPO") invalidated European Patent No. 0 505 500 owned by Applied Research Systems ARS Holdings, N.V., a wholly owned subsidiary of Serono International S.A. The Technical Board of Appeals ruled that Serono's claims failed for lack of enablement.

In February 2003, Serono brought suit against TKT in the District Court at The Hague in the Netherlands claiming that TKT's activities relating to Replagal (agalsidase alfa) infringe European Patent No. 0 505 500. The District Court proceedings at The Hague presently are stayed pending the outcome of this appeal by Serono. TKT will move to dismiss this case, and expects to prevail promptly.

Replagal is a fully human alpha-galactosidase A protein, produced using TKT's gene activation technology, intended for the long-term treatment of Fabry disease. It replaces the deficient alpha-galactosidase A with active enzyme to halt or reverse the disease progression. Since August 2001, Replagal has been approved for commercial use in 27 countries, including the 15 countries of the European Union. In the United States, Replagal is an investigational product.