UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

SCHEDULE 13G/A

Under the Securities Exchange Act of 1934

(Amendment No. 5)*

Aceragen, Inc.

(Name of Issuer)

Common Stock, $0.001 par value per share

(Title of Class of Securities)

00445F109

(CUSIP Number)

February 14, 2023

(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)

The information required in 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).

This Schedule 13G/A (#5), the Schedule 13G/A (#4) filed June 7, 2022, the Schedule 13G/A (#3) filed February 8, 2022, the Schedule 13G/A (#2) filed February 12, 2021, the Schedule 13G/A (#1) filed February 20, 2020, and the initial Schedule 13G filed September 4, 2018, collectively, (the “Schedule 13G”) relate to shares of Common Stock, $0.001 par value per share (the “Common Stock”), of Aceragen, Inc. (formerly Idera Pharmaceuticals, Inc.), a Delaware corporation (the “Issuer”).

Castellina Ventures Ltd. (“Castellina”) is a limited company organized under the laws of the British Virgin Islands whose principal business address and principal office address is 325 Waterfront Drive, Omar Hodge Building, 2nd Floor, Wickham’s Cay, Road Town, Tortola, British Virgin Islands. The Ballaison Trust is the sole shareholder of Castellina (“The Ballaison Trust”).

The Ballaison Trust is a trust established under the laws of New Zealand whose principal business address and principal office address is 14, rue de la Corraterie, PO Box 5209, CH-1211 Geneva 11. M&D Trustees SA is the trustee of The Ballaison Trust. The Ballaison Trust was established for the principal purpose of holding and preserving assets for the benefit of its beneficiaries.

Item 1(a). Name of Issuer:

Aceragen, Inc.

Item 1(b). Address of Issuer’s Principal Executive Offices:

505 Eagleview Blvd., Suite 212, Exton, Pennsylvania 19341

Item 2(a). Name of Person Filing:

(i) Castellina Ventures Ltd. and (ii) The Ballaison Trust

Item 2(b). Address of Principal Business Office or, if None, Residence:

The address of the principal business office of the Reporting Persons:

The address for Castellina is 325 Waterfront Drive, Omar Hodge Building, 2nd Floor, Wickham’s Cay, Road Town, Tortola, British Virgin Islands and the address for The Ballaison Trust if Rue de la Corraterie 14, PO Box 5209, 1211 Geneva 11.

Item 2(c). Citizenship:

Castellina is a limited company organized under the laws of the British Virgin Islands.

The Ballaison Trust is a trust formed under the laws of New Zealand.

Item 2(d). Title of Class of Securities:

Common Stock, par value $0.001 per share

Item 2(e). CUSIP Number:

00445F109

Item 3. Not Applicable.

Item 4. Ownership.

Castellina Ventures Ltd. and The Ballaison Trust may be each deemed to beneficially own the following:

The percentage of shares beneficially owned was calculated based on 8,461,063 shares of common stock of the Issuer outstanding as of January 17, 2023, as reported in the Issuer’s Current Report on Form 8-K filed with the SEC on January 17, 2023.

Item 5. Ownership of Five Percent or Less of a Class.

If this statement is being filed to report the fact that as of the date hereof the reporting person has ceased to be the beneficial owner of more than five percent of the class of securities, check the following. ☒

Item 6. Ownership of More than Five 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.

Not applicable.

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.

Date: February 14, 2023

Exhibit 99.1

Joint Filing Agreement

In accordance with Rule 13d-1(k) under the Securities and Exchange Act of 1934, the persons or entities named below agree to the joint filing on behalf of each of them of a statement on Schedule 13G (including amendments thereto) with respect to the shares of the Issuer and further agree that this joint filing agreement be included as an exhibit to this Schedule 13G. In evidence thereof, the undersigned, being duly authorized, have executed this Joint Filing Agreement as of February 14, 2023.