GeneDx: William Blair reports 5.2% passive stake

The reported 5.2% position includes sole voting power over 1,418,435 shares and sole dispositive power over 1,560,247 shares.

Available on EDGAR 11/06/2026 - 12:35 PM EST Accepted by SEC EDGAR 11/06/2026 - 12:35 PM EST Learn about SEC filing dates

Rhea-AI Filing Summary

GeneDx Holdings Corp. (WGS) common stock was the subject of a Schedule 13G ownership report from William Blair Investment Management, LLC. The investment manager reported beneficial ownership of 1,560,247 shares, or 5.2% of the class, as of September 30, 2026.

It reported sole voting power over 1,418,435 shares and sole dispositive power over 1,560,247 shares. Shared voting and shared dispositive power were each reported as zero.

Key Figures

Beneficially owned: 1,560,247 shares Percent of class: 5.2% Sole voting power: 1,418,435 shares +3 more

6 metrics

Beneficially owned 1,560,247 shares As of September 30, 2026

Percent of class 5.2% William Blair Investment Management, LLC's reported ownership

Sole voting power 1,418,435 shares As of September 30, 2026

Sole dispositive power 1,560,247 shares As of September 30, 2026

Shared voting power 0 shares As of September 30, 2026

Shared dispositive power 0 shares As of September 30, 2026

Key Terms

beneficially owned, Sole Voting Power, Sole Dispositive Power

3 terms

beneficially owned technical

"Amount beneficially owned: 1,560,247"

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.

Sole Voting Power technical

"Sole Voting Power 1,418,435.00"

Sole voting power is the exclusive right to cast votes attached to a shareholder’s stock without needing approval from anyone else. Like holding the only remote control for a TV, it lets that holder decide corporate matters such as board members, mergers, and policy changes, making it important to investors because it concentrates control and can strongly influence a company’s strategy and the value of its shares.

Sole Dispositive Power technical

"Sole Dispositive Power 1,560,247.00"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

FAQ

AI-generated questions and answers. How Rhea-AI works. Not financial advice.

How many WGS shares did William Blair Investment Management report owning?

William Blair Investment Management, LLC reported beneficial ownership of 1,560,247 GeneDx common shares, or 5.2% of the class, as of September 30, 2026. It reported sole voting power over 1,418,435 shares and sole dispositive power over 1,560,247 shares.

AI-generated analysis. How Rhea-AI works. Not financial advice.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

GeneDx Holdings Corp.

(Name of Issuer)

Common Stock

(Title of Class of Securities)

81663L200

(CUSIP Number)

09/30/2026

(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): 81663L200

1

Names of Reporting Persons

WILLIAM BLAIR INVESTMENT 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 1,418,435.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,560,247.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,560,247.00

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)

5.2 %

12

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13G

Item 1.
(a)	Name of issuer: GeneDx Holdings Corp.
(b)	Address of issuer's principal executive offices: 333 LUDLOW STREET, NORTH TOWER, 6TH FLOOR, STAMFORD, CONNECTICUT, 06902
Item 2.
(a)	Name of person filing: William Blair Investment Management, LLC
(b)	Address or principal business office or, if none, residence: 150 North Riverside Plaza, Chicago, IL 60606
(c)	Citizenship: Delaware
(d)	Title of class of securities: Common Stock
(e)	CUSIP Number(s): 81663L200
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: 1,560,247
(b)	Percent of class: 5.2%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 1,418,435
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1,560,247
	(iv) Shared power to dispose or to direct the disposition of: 0
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.
	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 acquired and are held in the ordinary course of business and 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.

WILLIAM BLAIR INVESTMENT MANAGEMENT, LLC

Signature:	Telmo Martins
Name/Title:	Chief Compliance Officer
Date:	11/06/2026