Insider filing report for Changes in Beneficial Ownership
- Schedule 13G & 13D forms are used to report a party's ownership of stock which exceeds 5% of a company's total stock issue.
- Schedule 13G is a shorter version of Schedule 13D with fewer reporting requirements.
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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549 |
SCHEDULE 13D
Under the Securities Exchange Act of 1934
|
Polaryx Therapeutics, Inc. (Name of Issuer) |
Common stock, par value $0.0001 per share ("Common Stock") (Title of Class of Securities) |
73110F100 (CUSIP Number) |
Alex Keun Mo Yang c/o Mstone Partners Healthcare Limited, 7/F, 80 Gloucester Road Wan Chai, K3, 00000 852-2155-0487 (Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications) |
01/29/2026 (Date of Event Which Requires Filing of This Statement) |
If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.
The information required on the remainder of this cover page shall not be deemed to be “filed” for the purpose of Section 18 of the
Securities Exchange Act of 1934 (“Act”) or otherwise subject to the liabilities of that section of the Act but shall be subject to all other
provisions of the Act (however, see the Notes).
SCHEDULE 13D
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| CUSIP No. | 73110F100 |
| 1 |
Name of reporting person
Mstone Partners Healthcare Limited | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
 (b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
WC | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
| ||||||||
| 6 | Citizenship or place of organization
HONG KONG
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
22,452,954.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
| ||||||||
| 13 | Percent of class represented by amount in Row (11)
47.4 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
CO |
Comment for Type of Reporting Person:
Based on 47,343,297 shares of common stock outstanding as of January 12, 2026.
SCHEDULE 13D
|
| CUSIP No. | 73110F100 |
| 1 |
Name of reporting person
MBstone Biotech Flagship Limited | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
WC | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
| ||||||||
| 6 | Citizenship or place of organization
HONG KONG
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
183,560.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
| ||||||||
| 13 | Percent of class represented by amount in Row (11)
0.4 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
CO |
Comment for Type of Reporting Person:
Based on 47,343,297 shares of common stock outstanding as of January 12, 2026.
SCHEDULE 13D
|
| CUSIP No. | 73110F100 |
| 1 |
Name of reporting person
Mstone Pediaorphan Singapore I Pte. Limited | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
WC | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
| ||||||||
| 6 | Citizenship or place of organization
SINGAPORE
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
108,282.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
| ||||||||
| 13 | Percent of class represented by amount in Row (11)
0.2 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
CO |
Comment for Type of Reporting Person:
Based on 47,343,297 shares of common stock outstanding as of January 12, 2026.
SCHEDULE 13D
|
| CUSIP No. | 73110F100 |
| 1 |
Name of reporting person
Alex Keun Mo Yang | ||||||||
| 2 | Check the appropriate box if a member of a Group (See Instructions)
(a)
(b)
| ||||||||
| 3 | SEC use only | ||||||||
| 4 |
Source of funds (See Instructions)
WC | ||||||||
| 5 |
Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)
| ||||||||
| 6 | Citizenship or place of organization
KOREA, REPUBLIC OF
| ||||||||
| Number of Shares Beneficially Owned by Each Reporting Person With: |
| ||||||||
| 11 | Aggregate amount beneficially owned by each reporting person
22,744,796.00 | ||||||||
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)
| ||||||||
| 13 | Percent of class represented by amount in Row (11)
48.0 % | ||||||||
| 14 | Type of Reporting Person (See Instructions)
IN |
Comment for Type of Reporting Person:
Based on 47,343,297 shares of common stock outstanding as of January 12, 2026.
SCHEDULE 13D
|
| Item 1. | Security and Issuer |
| (a) | Title of Class of Securities:
Common stock, par value $0.0001 per share ("Common Stock") |
| (b) | Name of Issuer:
Polaryx Therapeutics, Inc. |
| (c) | Address of Issuer's Principal Executive Offices:
South Tower, 140 E Ridgewood Avenue, Suite 415, Paramus,
NEW JERSEY
, 07652. |
| Item 2. | Identity and Background |
| (a) | This Schedule 13D is being filed jointly by (1) Mstone Partners Healthcare Limited, a private company limited by shares incorporated in Hong Kong ("Mstone"); (2) MBstone Biotech Flagship Limited, a private company limited by shares incorporated in Hong Kong ("MBstone"); (3) Mstone Pediaorphan Singapore I Pte. Limited, a private company limited by shares incorporated in Singapore ("Mstone Singapore"); and (4) Alex Keun Mo Yang (Mr. Yang, Mstone, MBStone and Mstone Singapore are collectively referred to herein as the "Reporting Persons"). The joint filing agreement of the Reporting Persons is attached as Exhibit 99.1 to this Schedule 13D. Mr. Yang is the founder and Chief Executive Officer of Mstone, the Chief Executive Officer of MBstone and the Chief Executive Officer of Mstone Singapore. Mr. Yang has voting power over the securities held by Mstone, MBstone and Mstone Singapore. Mr. Yang disclaims beneficial ownership of the securities reported in this Schedule 13D other than for the purpose of determining their obligations under Section 13(d) of the Act, and the filing of this Schedule 13D shall not be deemed an admission that Mr. Yang is the beneficial owner of such securities for any other purpose. |
| (b) | The principal business address of each of Mstone, MBstone and Mr. Yang is 7/F, 80 Gloucester Road, Wan Chai, Hong Kong. The principal business address of Mstone Singapore is 33 Ubi Ave 3#08-61 Vertex Tower A, Singapore 408868. |
| (c) | The principal business of Mstone is serving as a biotechnology, healthcare, and AI incubator. The principal business of MBstone is investing in biotech and healthcare companies. The principal business of Mstone Singapore is serving as a holding company for biopharmaceutical drug development. The principal occupation of Mr. Yang is to serve as the founder and Chief Executive Officer of Mstone, the Chief Executive Officer of MBstone and the Chief Executive Officer of Mstone Singapore, as well as Chief Executive Officer of Polaryx Therapeutics, Inc. (the "Company"). |
| (d) | During the last five years, none of the Reporting Persons has been convicted in a criminal proceeding (excluding traffic violations or similar misdemeanors). |
| (e) | During the last five years, none of the Reporting Persons has been a party to a civil proceeding of a judicial or administrative body of competent jurisdiction and as a result of such proceedings was or is subject to a judgment, decree, or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violations with respect at such laws. |
| (f) | Mstone is a private company limited by shares incorporated in Hong Kong. MBstone is a private company limited by shares incorporated in Hong Kong. Mstone Singapore is a private company limited by shares incorporated in Singapore. Mr. Yang is a citizen of South Korea. |
| Item 3. | Source and Amount of Funds or Other Consideration |
In aggregate, the Reporting Persons have voting and dispositive power over 22,744,796 shares of Common Stock. The aggregate purchase price of the shares of Common Stock purchased and currently owned by the Reporting Persons is $3,000,513. The source of the funding for the purchases of the shares of Common Stock was the general working capital of the Reporting Persons. The information set forth in Item 4 below is incorporated herein by reference. | |
| Item 4. | Purpose of Transaction |
The Reporting Persons own 48.0% of the Company in the aggregate, based on 47,343,297 shares of Common Stock outstanding as of January 12, 2026. Mr. Yang serves as Chief Executive Officer and as a member of the board of directors of the Company (the "Board"), and, in such capacity, may have influence over the corporate activities of the Company, including activities which may relate to items described in subparagraphs (a) through (j) of Item 4 of Schedule 13D. Except as described in this Schedule 13D, the Reporting Persons do not have any present plans or proposals that relate to or would result in any of the actions described in subparagraphs (a) through (j) of Item 4 of Schedule 13D, although, the Reporting Persons, at any time and from time to time, may review, reconsider and change their position and/or change their purpose and/or develop such plans and may seek to influence management or the Board with respect to the business and affairs of the Company and may from time to time consider pursuing or proposing such matters with advisors, the Company or other persons. | |
| Item 5. | Interest in Securities of the Issuer |
| (a) | The information set forth in Items 2 and 3 and on the cover pages of this Schedule 13D is incorporated by reference in its entirety into this Item 5. The percentages used in this Schedule 13D are calculated based on 47,343,297 shares of Common Stock outstanding as of January 12, 2026. |
| (b) | See Item 5(a) hereof. |
| (c) | N/A. |
| (d) | Except as otherwise described in this Item 5, no one other than the Reporting Persons has the right to receive, or the power to direct the receipt of, dividends from, or the proceeds from the sale of, any of the Common Stock beneficially owned by the Reporting Persons as described in this Item 5. |
| (e) | N/A. |
| Item 6. | Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer |
None. | |
| Item 7. | Material to be Filed as Exhibits. |
Exhibit 99.1 Joint Filing Agreement |
| 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.
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