Exhibit 2.1
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                           STATEMENT OF CONTROL PERSON


The Statement on this Schedule 13G dated June 4, 2004 with respect to the common
stock, $0.01 par value per share, of Transkaryotic Therapies Inc. is filed by
Samuel D. Isaly in accordance with the provisions of Rule 13d-1(b) and Rule
13d-1(k), respectively, as control person (HC) of OrbiMed Advisors LLC and
OrbiMed Capital LLC.

OrbiMed Advisors LLC and OrbiMed Capital LLC file this statement on Schedule 13G
in accordance with the provisions of Rule 13d-1(b) and Rule 13d-1(k),
respectively, as investment advisors (IA).