[SCHEDULE 13G] GeneDx Holdings Corp. SEC Filing

Rhea-AI Filing Summary

William Blair Investment Management, LLC (WBIM) filed a Schedule 13G on 30 Jun 2025 disclosing ownership of 1,631,402 GeneDx Holdings Corp. (WGS) common shares, equal to 5.7 % of the outstanding class. The investment adviser has sole voting power over 1,491,038 shares and sole dispositive power over the full 1.63 million shares; no shared authority is reported. The filing was made under Rule 13d-1(b), indicating the position is held in the ordinary course of business rather than to influence control. No group membership, subsidiary involvement, or special arrangements are disclosed. Crossing the 5 % threshold requires initial reporting and signals the entrance of a mid-size institutional investor into the company’s shareholder base.

Positive

• William Blair Investment Management disclosed a 5.7 % passive stake, adding a reputable institutional investor to WGS’s shareholder base.

Negative

• None.

Insights

Securities Analyst

TL;DR: 5.7 % stake by WBIM adds credible institutional holder; impact modest but supportive.

WBIM’s disclosure introduces a respected active manager into WGS’s register. While 1.63 million shares is not large in absolute terms, it exceeds the 5 % reporting threshold, suggesting conviction in the issuer’s genomic-testing strategy. Sole voting and dispositive control imply WBIM can act quickly on buy/sell decisions, potentially adding to share-price volatility around fundamental catalysts. However, no activist intent is stated, keeping governance risk low. Overall, the filing marginally strengthens the shareholder mix and could improve liquidity, but it is unlikely to materially change the investment thesis on its own.

Portfolio Manager

TL;DR: New mid-tier institution may widen coverage and liquidity; limited strategic implications.

From a portfolio-flow perspective, WBIM’s 5.7 % holding equates to roughly two weeks of typical WGS trading volume, meaning entry or exit can move the tape. The firm’s growth-equity bias aligns with WGS’s high-beta profile, potentially attracting peer managers once SEC visibility increases. Nevertheless, without board representation or activist language, this is a passive stake. Investors should view the news as a mild vote of confidence rather than a transformational event.

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)

06/30/2025

(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)

SCHEDULE 13G

CUSIP No. 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 1,491,038.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,631,402.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,631,402.00

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)

5.7 %

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 No.: 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: 1,631,402
(b)	Percent of class: 5.7%
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 1,491,038
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1,631,402
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
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:	Walter R. Randall, Jr.
Name/Title:	Chief Compliance Officer
Date:	06/30/2025

FAQ

How many GeneDx (WGS) shares does William Blair Investment Management own?

The firm reports beneficial ownership of 1,631,402 common shares.

What percentage of GeneDx’s outstanding shares does this represent?

The stake equals 5.7 % of the company’s common stock.

Does William Blair Investment Management have shared voting power in WGS?

No. The filing lists 0 shared voting and dispositive power; all authority is held solely.

Is the investment considered activist or passive?

The Schedule 13G was filed under Rule 13d-1(b), indicating a passive investment held in the ordinary course of business.

Why was the filing required on 30 June 2025?

Crossing the 5 % ownership threshold triggers a mandatory Schedule 13G filing within 10 days.