Exhibit 5.3
[On letterhead of Orrick, Herrington & Sutcliffe LLP]
September 28, 2009
Transition Therapeutics Inc.
101 College Street, Suite 220
Toronto, Ontario, Canada M5G 1L7
Re: Registration Statement on Form F-10 of Transition Therapeutics Inc.
Ladies and Gentlemen:
We hereby consent to the reference to our firm under the heading “Legal Matters” in the short form base prospectus filed as part of this Registration Statement on Form F-10. By giving this consent, we do not admit that we are within the category of persons whose consent is required under Section 7 of the Securities Act of 1933, as amended, and the rules and regulations promulgated thereunder.
Yours truly,
/s/ Orrick, Herrington & Sutcliffe LLP
