Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
HEN STEWART
  2. Issuer Name and Ticker or Trading Symbol
Altus Pharmaceuticals Inc. [ALTU]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director __X__ 10% Owner
_____ Officer (give title below) _____ Other (specify below)
(Last)
(First)
(Middle)
WARBURG PINCUS PRIVATE EQUITY VIII, L.P., 466 LEXINGTON AVENUE
3. Date of Earliest Transaction (Month/Day/Year)
01/31/2006
(Street)

NEW YORK, MA 10017
4. If Amendment, Date Original Filed(Month/Day/Year)
6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)
7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 01/31/2006(1)   C   3,589,246 (2) (3) A (3) 3,589,246 (2) (3) I Shares held by Warburg Pincus Private Equity VIII, L.P. (4)

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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)
6. Date Exercisable and Expiration Date
(Month/Day/Year)
7. Title and Amount of Underlying Securities
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)
10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)
11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Series C Convertible Preferred Stock (3) 01/31/2006(1)   C     3,589,246 (2) (3) 05/21/2004 01/31/2006(1) Common Stock 3,589,246 (2) (3) $ 0 0 I Shares held by Warburg Pincus Private Equity VIII, L.P. (4)
Warrant $ 9.802 01/31/2006(1)   C   717,917 (5)   05/21/2004 05/21/2011 Common Stock 717,917 (5) $ 9.802 717,917 (5) I Shares held by Warburg Pincus Private Equity VIII, L.P. (4)

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
HEN STEWART
WARBURG PINCUS PRIVATE EQUITY VIII, L.P.
466 LEXINGTON AVENUE
NEW YORK, MA 10017
  X   X    

Signatures

 /s/ Marianne Staniunas, Attorney in Fact   02/01/2006
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) This is the date of the closing of the Issuer's initial public offering.
(2) Includes dividends that had been accruing on the Series C Convertible Preferred Stock and which were paid out in 325,995 shares of common stock as of the date of the closing of the Issuer's intial public offering.
(3) All outstanding shares of the Issuer's Series C Convertible Preferred Stock converted to common stock at a rate of .4401933369 - to- 1 upon the completion of the Issuer's initial public offering.
(4) The stockholder is Warburg Pincus Private Equity VIII, L.P. ("WP VIII"). Warburg Pincus Partners, LLC ("WPP LLC"), a subsidiary of Warburg Pincus & Co. ("WP"), is the sole general partner of WP VIII. WP VIII is managed by Warburg Pincus LLC ("WP LLC"). Mr. Hen is a general partner of WP and managing director and member of WP LLC. All shares indicated as owned by Mr. Hen are included because of his affiliation with the Warburg Pincus entities. Mr. Hen disclaims beneficial ownership of all shares held by the Warburg Pincus entities.
(5) Warrants were automatically adjusted on a basis of .4401933369 - to- 1 upon closing of the Issuer's public offering. The number of adjusted warrants reported are exercisable for common stock on a 1 for 1 basis.

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