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Ultragenyx Pharmaceutical Inc. (RARE) shares were reported as beneficially owned by Madison Avenue International LP, which directly owned 6,307,798 shares as of October 20, 2026. Madison Avenue Partners, LP, EMAI Management, LLC, Madison Avenue GP, LLC, Caraway Jackson Investments LLC and Eli Samaha may also be deemed beneficial owners of those same shares through their stated relationships with Madison Avenue International LP.
The six reporting persons reported shared voting and dispositive power over 6,307,798 shares. The position represented approximately 6.4% of the common stock, based on 98,588,873 shares outstanding as of June 30, 2026.
Beneficially owned shares6,307,798 sharesMadison Avenue International LP, as of October 20, 2026
Beneficial ownershipApproximately 6.4%Reporting persons, as of October 20, 2026
Common shares outstanding98,588,873 sharesAs of June 30, 2026
Key Terms
beneficially owned, Shared Voting Power, Shared Dispositive Power
3 terms
beneficially ownedregulatory
"beneficially owned 6,307,798 shares of Common Stock"
Beneficially owned describes securities or assets where a person has the economic rights and control—such as the right to receive dividends and to direct voting—even if legal title is held in another name. Think of it like having the keys and using a car that’s registered to someone else: you get the benefits and make decisions. Investors care because beneficial ownership reveals who truly controls value and voting power, affecting corporate decisions and takeover dynamics.
Shared Voting Powerregulatory
"Shared Voting Power 6,307,798.00"
Shared voting power occurs when two or more parties jointly have the right to vote or decide how a block of company shares is cast, like co-owners who must agree before moving a piece of furniture. Investors care because who controls voting rights affects board elections, major corporate decisions and takeover outcomes, and shared control can alter regulatory disclosures and the practical influence any holder has over a company’s direction and value.
Shared Dispositive Powerregulatory
"Shared Dispositive Power 6,307,798.00"
FAQ
AI-generated questions and answers. How Rhea-AI works. Not financial advice.
How many RARE shares did Madison Avenue International LP beneficially own?
Madison Avenue International LP beneficially owned 6,307,798 shares as of October 20, 2026.
What percentage of RARE did the reporting persons beneficially own?
The reporting persons may be deemed to have beneficially owned approximately 6.4% of Ultragenyx common stock as of October 20, 2026. The percentage uses 98,588,873 shares outstanding as of June 30, 2026.
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549
SCHEDULE 13G
UNDER THE SECURITIES EXCHANGE ACT OF 1934
Ultragenyx Pharmaceutical Inc.
(Name of Issuer)
Common Stock, $0.001 par value (the "Common Stock")
(Title of Class of Securities)
90400D108
(CUSIP Number)
10/13/2026
(Date of Event Which Requires Filing of this Statement)
Check the appropriate box to designate the rule pursuant to which this Schedule is filed:
Rule 13d-1(b)
Rule 13d-1(c)
Rule 13d-1(d)
schemaVersion:
SCHEDULE 13G
CUSIP Number(s):
90400D108
1
Names of Reporting Persons
Madison Avenue International LP
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
CAYMAN ISLANDS
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,307,798.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,307,798.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,307,798.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
6.4 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
CUSIP Number(s):
90400D108
1
Names of Reporting Persons
Madison Avenue Partners, LP
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,307,798.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,307,798.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,307,798.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
6.4 %
12
Type of Reporting Person (See Instructions)
PN
SCHEDULE 13G
CUSIP Number(s):
90400D108
1
Names of Reporting Persons
EMAI Management, LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,307,798.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,307,798.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,307,798.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
6.4 %
12
Type of Reporting Person (See Instructions)
OO
SCHEDULE 13G
CUSIP Number(s):
90400D108
1
Names of Reporting Persons
Madison Avenue GP, LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,307,798.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,307,798.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,307,798.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
6.4 %
12
Type of Reporting Person (See Instructions)
OO
SCHEDULE 13G
CUSIP Number(s):
90400D108
1
Names of Reporting Persons
Caraway Jackson Investments LLC
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
DELAWARE
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,307,798.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,307,798.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,307,798.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
6.4 %
12
Type of Reporting Person (See Instructions)
OO
SCHEDULE 13G
CUSIP Number(s):
90400D108
1
Names of Reporting Persons
Eli Samaha
2
Check the appropriate box if a member of a Group (see instructions)
(a)
(b)
3
Sec Use Only
4
Citizenship or Place of Organization
UNITED STATES
Number of Shares Beneficially Owned by Each Reporting Person With:
5
Sole Voting Power
0.00
6
Shared Voting Power
6,307,798.00
7
Sole Dispositive Power
0.00
8
Shared Dispositive Power
6,307,798.00
9
Aggregate Amount Beneficially Owned by Each Reporting Person
6,307,798.00
10
Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)
11
Percent of class represented by amount in row (9)
6.4 %
12
Type of Reporting Person (See Instructions)
IN
SCHEDULE 13G
Item 1.
(a)
Name of issuer:
Ultragenyx Pharmaceutical Inc.
(b)
Address of issuer's principal executive offices:
60 Leveroni Court, Novato, CA 94949
Item 2.
(a)
Name of person filing:
The names of the persons filing this statement on Schedule 13G (collectively, the "Reporting Persons") are:
* Madison Avenue International LP,
* Madison Avenue Partners, LP,
* EMAI Management, LLC,
* Madison Avenue GP, LLC,
* Caraway Jackson Investments LLC, and
* Eli Samaha.
(b)
Address or principal business office or, if none, residence:
The principal business address for each of the Reporting Persons is 150 East 58th St, 14th Fl, New York, NY 10155.
(c)
Citizenship:
Madison Avenue International LP is a Cayman Islands exempted limited partnership. Madison Avenue Partners, LP is a Delaware limited partnership. Each of EMAI Management, LLC, Madison Avenue GP, LLC and Caraway Jackson Investments LLC is a Delaware limited liability company. Mr. Samaha is a citizen of the United States of America.
(d)
Title of class of securities:
Common Stock, $0.001 par value (the "Common Stock")
(e)
CUSIP Number(s):
90400D108
Item 3.
If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)
Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)
Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)
Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)
Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)
An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)
An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)
A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)
A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)
A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)
A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J),
please specify the type of institution:
(k)
Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.
Ownership
(a)
Amount beneficially owned:
As of October 20, 2026, Madison Avenue International LP beneficially owned 6,307,798 shares of Common Stock.
Madison Avenue Partners, LP and Madison Avenue GP, LLC, as the investment manager and general partner of Madison Avenue International LP, respectively, may be deemed to be the beneficial owner of the Common Stock owned directly by Madison Avenue International LP.
EMAI Management, LLC, as the general partner of Madison Avenue Partners, LP, may be deemed to be the beneficial owner of the Common Stock owned directly by Madison Avenue International LP.
Caraway Jackson Investments LLC, as the owner of Madison Avenue GP, LLC, may be deemed to be the beneficial owner of the Common Stock owned directly by Madison Avenue International LP.
Mr. Samaha, as the non-member manager of Madison Avenue GP, LLC, the managing member of EMAI Management, LLC, and the majority owner of Caraway Jackson Investments LLC, may be deemed to be the beneficial owner of the Common Stock owned by Madison Avenue International LP.
(b)
Percent of class:
The following percentage is based on 98,588,873 Common Stock outstanding as of June 30, 2026, as disclosed in the Issuer's Quarterly Report on Form 10-Q, filed with the Securities and Exchange Commission on August 5, 2026.
As of October 20, 2026, the Reporting Persons may be deemed to have beneficially owned approximately 6.4% of the outstanding Common Stock.
(c)
Number of shares as to which the person has:
(i) Sole power to vote or to direct the vote:
See Cover Pages Items 5-9.
(ii) Shared power to vote or to direct the vote:
See Cover Pages Items 5-9.
(iii) Sole power to dispose or to direct the disposition of:
See Cover Pages Items 5-9.
(iv) Shared power to dispose or to direct the disposition of:
See Cover Pages Items 5-9.
Item 5.
Ownership of 5 Percent or Less of a Class.
Not Applicable
Item 6.
Ownership of more than 5 Percent on Behalf of Another Person.
Not Applicable
Item 7.
Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
Not Applicable
Item 8.
Identification and Classification of Members of the Group.
If a group has filed this schedule pursuant to §240.13d-1(b)(1)(ii)(K), so indicate under Item 3(k) and attach an exhibit stating the identity and Item 3 classification of each member of the group. If a group has filed this schedule pursuant to §240.13d-1(c) or §240.13d-1(d), attach an exhibit stating the identity of each member of the group.
See Exhibit A.
Item 9.
Notice of Dissolution of Group.
Not Applicable
Item 10.
Certifications:
By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.
SIGNATURE
After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.
Madison Avenue International LP
Signature:
/s/ Eli Samaha
Name/Title:
Eli Samaha, as Manager of Madison Avenue GP, LLC, its General Partner
Date:
10/20/2026
Madison Avenue Partners, LP
Signature:
/s/ Eli Samaha
Name/Title:
Eli Samaha, as Managing Member of EMAI Management, LLC, its General Partner
