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Exhibit 99.2


Risks Related to Patent Litigation

    Patent Litigation. The biotechnology industry has been characterized by
significant litigation and interference proceedings regarding patents, patent
applications and other intellectual property rights, and many companies in the
biotechnology industry have attempted to employ intellectual property litigation
to gain or preserve a competitive advantage. For example, there has been
substantial intellectual property litigation between suppliers of erythropoietin
throughout the world.

    In April 1997, Amgen Inc. filed a civil action in the U.S. District Court in
Massachusetts against the Company and Hoechst Marion Roussel, Inc. ("HMRI"), the
Company's collaborative partner. The complaint in the action alleged that the
Company's Gene Activation development program for the production of GA-EPO and
processes for producing GA-EPO infringe on Amgen's U.S. Patent Numbers
5,547,933, 5,618,698, and 5,621,080 and requested that TKT and HMRI be enjoined
from making, using, or selling GA-EPO and that the court award Amgen monetary
damages.

    In November 1997, TKT and HMRI filed a Motion for Summary Judgment. On the
same date, Amgen filed a Motion for Summary Judgment of Infringement. TKT and
HMRI opposed that motion, stating that there had been no infringement.

    In April 1998, the U.S. District Court granted TKT and HMRI's Motion for
Summary Judgment and denied Amgen's Motion for Summary Judgment on the ground
that all of TKT and HMRI's GA-EPO related activities to date had been solely for
uses reasonably related to the production of information for submission to the
FDA for regulatory approval and, under the Waxman-Hatch Act, do not constitute
acts of patent infringement. The Court ordered Amgen's remaining claim for
declaratory judgment of future infringement administratively closed, to be
reopened upon motion of either party for good cause shown. The Court also stated
that the issuance by the FDA of a product license presumably would show good
cause to reopen that claim. Finally, the Court stated that, should the case be
reopened and should Amgen seek preliminary equitable relief, the Court will
combine the hearing on a preliminary injunction with trial on the merits. The
Company expects that the case will be reopened.

    Should the case be reopened, the Company can provide no assurance as to the
outcome of the litigation. A decision by the court in Amgen's favor, including
the issuance of an injunction against the making, use or sale of GA-EPO by the
Company and HMRI in the United States, or any other conclusion of such
litigation in a manner adverse to the Company and HMRI, would have a material
adverse effect on the Company's business, financial condition, and results of
operations.

    There can be no assurance that the Company will not in the future become
subject, in the United States or any other country, to additional patent
infringement claims, interferences and other litigation involving patents, or
any patents that may issue on any pending patent applications, including Amgen
patent applications.

    The defense and prosecution of intellectual property suits and related legal
and administrative proceedings can be both costly and time consuming. Litigation
and interference proceedings could result in substantial expense to the Company
or its corporate partner and significant diversion of effort by the Company's
technical and management personnel. An adverse determination in litigation to
which the Company may become a 


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party could subject the Company to significant liabilities to third parties or
require the Company to seek licenses from third parties. Although a number of
patent and intellectual property disputes in the biotechnology area have been
settled through licensing or similar arrangements, costs associated with any
such arrangement may be substantial and could include ongoing royalties.
Furthermore, there can be no assurance that necessary licenses would be
available to the Company or its corporate partner or would be available on
acceptable terms. Adverse determinations in a judicial or administrative
proceeding or failure to obtain necessary licenses could prevent the Company or
its corporate partner from manufacturing and selling some or all of its
products, which would have a material adverse effect on the Company's business,
financial condition and results of operations.

    With respect to gene therapy technology, the Company requested, and the U.S.
Patent and Trademark Office (the "PTO"), declared in January 1996, an
interference regarding a third party's issued patent with broad claims to ex
vivo gene therapy. The participants in the interference are TKT, Genetic
Therapy, Inc. (a wholly-owned subsidiary of Novartis AG), Syntex (U.S.A.) (a
wholly-owned subsidiary of Roche Holdings, Inc.), and Somatix. Somatix
subsequently merged into Cell Genesys, Inc. With the possible exception of the
patent involved in the interference, the Company believes its Transkaryotic
Therapy technology does not infringe on patents issued to date. The PTO
proceeding will determine the patentability of the subject matter of the
interference and which of the parties first developed this subject matter. The
process to resolve the interference can take many years. The outcome of
interferences can be quite variable: for example, none of the four parties may
receive the desired claims, one party may prevail, or a settlement involving two
or more of the parties may be reached. There can be no assurance that TKT will
prevail in this interference or that, even if it does prevail, that the Company
can meaningfully protect its proprietary position. In the event TKT does not
prevail in the interference, a January 1997 Federal Trade Commission (the "FTC")
decision may then be relevant. The FTC entered a consent order to resolve
anticompetitive concerns raised by the merger of Ciba-Geigy Limited and Sandoz
Limited into the newly formed Novartis AG. As part of the consent order, the
constituent entities of Novartis will be required to provide all gene therapy
researchers and developers with non-exclusive licenses to the patent upon which
Novartis is involved in the interference. The Company has entered into an
agreement with Somatix under which the Company's ability to market its non-viral
gene therapy products will not be affected should Somatix win the interference.

    Should any of its competitors have filed additional patent applications in
the U.S. that claim technology also invented by the Company, the Company may
have to participate in additional interference proceedings declared by the PTO,
all of which could result in substantial cost to the Company to determine its
rights or potential loss of rights.