EXHIBIT A

POWER OF ATTORNEY

	KNOW ALL MEN BY THESE PRESENTS, that each
person whose signature appears below hereby
constitutes and appoints Raymond Charest, Alexia
Pearsall and Jonathan J. Fleming, and each of
them, with full power to act without the other,
his true and lawful attorney-in-fact and agent,
with full power of substitution, for him and in
his name, place and stead, in any and all
capacities (until revoked in writing) to sign
any and all instruments, certificates and
documents required to be executed on behalf of
himself as an individual or in his capacity as
a general partner or authorized signatory, as
the case may be, on behalf of any of Oxford
Bioscience Partners IV L.P., mRNA II L.P.,
or OBP Management IV L.P., pursuant to
section 13 or 16 of the Securities Exchange
Act of 1934, as amended (the "Exchange Act"),
and any and all regulations promulgated
thereunder and to file the same, with all
exhibits thereto, and any other documents in
connection therewith, with the Securities and
Exchange Commission, and with any other entity
when and if such is mandated by the Exchange
Act or by the By-laws of the National Association
of Securities Dealers, Inc., granting unto said
attorney-in-fact and agent full power and
authority to do and perform each and every act and
thing requisite and necessary fully to all intents
and purposes as he might or could do in person
thereby ratifying and confirming all that said
attorney-in-fact and agent, or his substitute or
substitutes, may lawfully do or cause to be done
by virtue hereof, or may have done in connection
with the matters described above.

IN WITNESS WHEREOF, this Power of Attorney has
been signed as of the 8th day of April, 2004.


OXFORD BIOSCIENCE PARTNERS IV L.P.
by its General Partner, OBP MANAGEMENT IV L.P.

By: /s/ Jonathan Fleming
Name:  Jonathan J. Fleming
Title:  General Partner


MRNA FUND II L.P.
By its General Partner, OBP MANAGEMENT IV L.P.
By: /s/ Jonathan Fleming
Name:  Jonathan J. Fleming
Title:  General Partner


OBP MANAGEMENT IV L.P.
By:/s/ Jonathan Fleming
Name:  Jonathan J. Fleming
Title:  General Partner



/s/ Jeffrey T. Barnes
Jeffrey T. Barnes



/s/ Mark P. Carthy
Mark P. Carthy



/s/ Jonathan J. Fleming
Jonathan J. Fleming



/s/ Michael E. Lytton
Michael E. Lytton



/s/ Alan G. Walton
Alan G. Walton