Sec Form 3 Filing - Yang Alex Keun Mo @ Polaryx Therapeutics, Inc. - 2026-01-29

FORM 3 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 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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1. Name and Address of Reporting Person Yang Alex Keun Mo 2. Issuer Name and Ticker or Trading Symbol Polaryx Therapeutics, Inc. [ PLYX] 5. Relationship of Reporting Person(s) to Issuer (Check all applicable) X __ Director X __ 10% Owner X __ Officer (give title below) _____ Other (specify below) Chief Executive Officer (Last) (First) (Middle) SOUTH TOWER, 140 E RIDGEWOOD AVENUE,, SUITE 415 3. Date of Earliest Transaction (MM/DD/YY) 01/29/2026 (Street) PARAMUS, NJ07652 4. If Amendment, Date Original Filed (MM/DD/YY) 6. Individual or Joint/Group Filing (Check Applicable Line) _____ Form filed by One Reporting Person __ X __ 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 (MM/DD/YY) 2A. Deemed Execution Date, if any (MM/DD/YY) 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 1,400,000 ( 1 ) D Common Stock 22,452,954 I By Mstone Partners Healthcare Limited ( 2 ) Common Stock 183,560 I By MBstone Biotech Flagship Limited ( 3 ) Common Stock 108,282 I By Mstone Pediaorphan Singapore I Pte. Limited ( 4 )

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 (MM/DD/YY) 3A. Deemed Execution Date, if any (MM/DD/YY) 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 (MM/DD/YY) 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

Reporting Owners Reporting Owner Name / Address Relationships Director 10% Owner Officer Other Yang Alex Keun Mo SOUTH TOWER, 140 E RIDGEWOOD AVENUE, SUITE 415 PARAMUS, NJ07652 X X Chief Executive Officer Mstone Partners Healthcare Ltd 7/F, 80 GLOUCESTER ROAD WANCHAI, K3 X X Signatures /s/ Alex Keun Mo Yang 01/29/2026 Signature of Reporting Person Date /s/ Alex Keun Mo Yang, Chief Executive Officer of Mstone Partners Healthcare Limited 01/29/2026 Signature of Reporting Person Date

Explanation of Responses:

( 1 )Includes (i) 148,500 restricted stock units ("RSUs"), which will vest on March 1, 2026, (ii) 330,000 RSUs, which will vest in two equal installments on November 1, 2026 and November 1, 2027 and (iii) 450,000 RSUs, which will vest in four equal installments on September 1, 2026, September 1, 2027, September 1, 2028 and September 1, 2029, in each case subject to the Reporting Person's continued service to the Issuer or its subsidiaries, Mstone Partners Healthcare Limited ("Mstone") or its affiliates, or Curestone Partners Platform Limited or its affiliates. The RSUs are not deliverable unless and until the Issuer consummates a change in control within seven years of the grant date of such RSUs. ( 2 )Alex Keun Mo Yang is the founder and Chief Executive Officer of Mstone. Mr. Yang disclaims beneficial ownership over any of the reported securities, except to the extent of his pecuniary interest therein. ( 3 )Mr. Yang is the Chief Executive Officer of MBstone Biotech Flagship Limited. Mr. Yang disclaims beneficial ownership over any of the reported securities, except to the extent of his pecuniary interest therein. ( 4 )Mr. Yang is the Chief Executive Officer of Mstone Pediaorphan Singapore I Pte. Limited. Mr. Yang disclaims beneficial ownership over any of the reported securities owned, except to the extent of his pecuniary interest therein.

Remarks: Exhibit 24 - Power of Attorney Mstone, MBstone Biotech Flagship Limited and Mstone Pediaorphan Singapore I Pte. Limited may each be deemed a director by deputization of the Issuer by virtue of the fact that Mr. Yang serves on the board of directors of the Issuer and is the Chief Executive Officer of each of the entities.

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).

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