Schedule 13D/A: Casdin and Meister Disclose Double-Digit Holdings in GeneDx (WGS)

Rhea-AI Filing Summary

Amendment No. 9 to the Schedule 13D for GeneDx Holdings Corp. updates ownership and voting information for a group led by Eli Casdin and Keith Meister. The filing shows that Eli Casdin beneficially owns 3,599,671 shares (12.4%) and Keith A. Meister beneficially owns 3,630,826 shares (12.5%) of the Class A common stock, based on 28,726,248 shares outstanding as of July 24, 2025.

The filing attributes 3,007,164 shares (10.5%) to Casdin Partners Master Fund, L.P. and 3,058,629 shares (10.6%) to investment funds advised by Corvex Management LP. Certain reported holdings include shares issuable upon exercise of warrants and vested options (including 204,141 private placement warrants exercisable at $379.50 per share). The funds for the purchases listed were from the working capital of Casdin Partners Master Fund, L.P. Transactions in the past 60 days are reported in Exhibit B. The Amendment supplements earlier Schedule 13D filings and includes a joint filing agreement and transaction schedule as exhibits.

Positive

• Material disclosure of ownership: Two principal reporting persons disclose >10% holdings each, providing clear transparency to the market.
• Funding clarity: Purchases for the Casdin-held shares were made from the working capital of Casdin Partners Master Fund, L.P., with no borrowed funds used for purchases (other than ordinary working capital borrowings).
• Exhibits filed: Joint Filing Agreement and a Schedule of Transactions (Exhibits A and B) are included to document coordination and recent transactions.

Negative

• Potential dilution: The reported holdings include 204,141 private placement warrants exercisable at $379.50 per share and various vested options and RSU-related shares that can increase the share count.
• Concentrated ownership: Significant shared beneficial ownership and shared voting power are concentrated among related parties, which could centralize control in a small group of affiliated holders.

Insights

Financial Analyst

TL;DR: Two activist-aligned investors report double-digit stakes, representing a material ownership position that may affect corporate governance.

The filing documents that Eli Casdin and Keith Meister, through affiliated vehicles, each hold roughly 12% of Class A stock, with institutional vehicles owning just over 10% each. These stakes are material relative to the 28.7 million shares outstanding and could influence board or strategic outcomes. The inclusion of exercisable private placement warrants and vested options increases the potential share count that these parties can control. Funding was from working capital of the Casdin fund, not borrowed funds for purchases. Overall, this is a clear, material ownership disclosure that investors should treat as a governance development.

Corporate Governance Expert

TL;DR: Reported shared voting and dispositive power across related entities creates a concentrated, coordinated ownership bloc exceeding 10%.

The Schedule 13D/A shows shared voting and dispositive power among related entities (CMLS Holdings LLC, C-LSH LLC, M-LSH LLC, Casdin entities, and Corvex-related funds), resulting in concentrated influence. The filing identifies specific securities that expand voting potential, including private placement warrants and vested options. Exhibits confirm recent open-market transactions. The structure and level of ownership are sufficiently material to be considered impactful for governance and strategic discussions at the issuer.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 9)

GeneDx Holdings Corp.

(Name of Issuer)

Class A common stock, par value $0.0001 per share

(Title of Class of Securities)

81663L200

(CUSIP Number)

Eli Casdin and Keith Meister
c/o Corvex Management LP, 667 Madison Avenue
New York, NY, 10065
(212) 474-6700

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

08/22/2025

(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

CUSIP No. 81663L200

1

Name of reporting person

CMLS Holdings LLC

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)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 537,285.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 537,285.00

11

Aggregate amount beneficially owned by each reporting person

537,285.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.9 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

C-LSH LLC

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)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 537,285.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 537,285.00

11

Aggregate amount beneficially owned by each reporting person

537,285.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.9 %

14

Type of Reporting Person (See Instructions)

HC, OO

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

M-LSH LLC

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)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 537,285.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 537,285.00

11

Aggregate amount beneficially owned by each reporting person

537,285.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

1.9 %

14

Type of Reporting Person (See Instructions)

HC, OO

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

Casdin Capital, LLC

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)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,007,164.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,007,164.00

11

Aggregate amount beneficially owned by each reporting person

3,007,164.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

10.5 %

14

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

Casdin Partners Master Fund, L.P.

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

CAYMAN ISLANDS

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,007,164.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,007,164.00

11

Aggregate amount beneficially owned by each reporting person

3,007,164.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

10.5 %

14

Type of Reporting Person (See Instructions)

PN

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

Casdin Partners GP, LLC

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)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,026,411.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,026,411.00

11

Aggregate amount beneficially owned by each reporting person

3,026,411.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

10.5 %

14

Type of Reporting Person (See Instructions)

OO

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

Eli Casdin

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)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 35,975.00
8	Shared Voting Power 3,563,696.00
9	Sole Dispositive Power 35,975.00
10	Shared Dispositive Power 3,563,696.00

11

Aggregate amount beneficially owned by each reporting person

3,599,671.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

12.4 %

14

Type of Reporting Person (See Instructions)

IN, HC

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

Keith A. Meister

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)

OO

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 34,912.00
8	Shared Voting Power 3,595,914.00
9	Sole Dispositive Power 34,912.00
10	Shared Dispositive Power 3,595,914.00

11

Aggregate amount beneficially owned by each reporting person

3,630,826.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

12.5 %

14

Type of Reporting Person (See Instructions)

IN, HC

SCHEDULE 13D

CUSIP No. 81663L200

1

Name of reporting person

Corvex Management LP

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)

AF

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,058,629.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,058,629.00

11

Aggregate amount beneficially owned by each reporting person

3,058,629.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

10.6 %

14

Type of Reporting Person (See Instructions)

IN, PN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Class A common stock, par value $0.0001 per share
(b)	Name of Issuer: GeneDx Holdings Corp.
(c)	Address of Issuer's Principal Executive Offices: 333 Ludlow Street, North Tower, 8th Floor, Stamford, CONNECTICUT , 06902.
Item 1 Comment: This Amendment No. 9 (the "Amendment") supplements the information set forth in the Schedule 13D (the "Schedule 13D") filed with the United States Securities and Exchange Commission (the "SEC") on August 2, 2021, as amended as of January 19, 2022, May 3, 2022, December 5, 2022, February 1, 2023, April 20, 2023, November 17, 2023, May 31, 2024 and May 7, 2025 by CMLS Holdings LLC, Keith Meister, Eli Casdin and the other Reporting Persons named therein, relating to the shares of Class A common stock, par value $0.0001 per share ("Shares"), of GeneDx Holdings Corp. (formerly known as Sema4 Holdings Corp., the "Issuer"). Capitalized terms used but not defined herein shall have the meanings ascribed to them in the Schedule 13D. The information set forth in response to each separate Item below shall be deemed to be a response to all Items where such information is relevant. Item 3 and 5 to the Schedule 13D are supplementally amended as follows. Information with respect to each Reporting Person is given solely by such Reporting Person and no Reporting Person assumes responsibility for the accuracy or completeness of the information furnished by another Reporting Person, except as otherwise provided in Rule 13d-1(k).
Item 3.	Source and Amount of Funds or Other Consideration
	The funds for the purchase of the Shares listed in Exhibit B came from the working capital of Casdin Partners Master Fund, L.P, an investment fund advised by Casdin Capital, LLC, of which Mr. Casdin is the managing member. No borrowed funds were used to purchase the Shares, other than borrowed funds used for working capital purposes in the ordinary course of business.
Item 5.	Interest in Securities of the Issuer
(a)	The information set forth in the facing pages of this Schedule 13D with respect to the sole and shared beneficial ownership and percentage of beneficial ownership of Shares by the Reporting Persons is hereby incorporated by reference into this Item 5. The information in Item 5(b) below is hereby incorporated by reference into this Item 5(a). References to percentage ownership of Shares in this Statement are based upon the 28,726,248 Shares stated to be outstanding as of July 24, 2025 in the Issuer's Form 10-Q filed with the SEC on July 29, 2025. The filing of this Statement shall not be construed as an admission that a Reporting Person beneficially owns those Shares held by any other Reporting Person
(b)	Eli Casdin has the sole power to vote or direct the vote and sole power to dispose or to direct the disposition of 35,975 Shares and shared power to vote or to direct the vote and shared power to dispose or to direct the disposition of 3,563,696 Shares. The Shares reflected as beneficially owned by Mr. Casdin include 333,144 Shares and 204,141 Shares issuable upon the exercise of 204,141 private placement warrants of the Issuer. On September 3, 2021, each private placement warrant became exercisable to purchase one Share at a price of $379.50 per share, subject to adjustment, as described in the definitive proxy statement of the Issuer (File No. 001-39482) filed with the SEC on July 2, 2021. CMLS Holdings LLC is the record holder of these Shares and warrants. The Board of Managers of CMLS Holdings LLC is comprised of Mr. Casdin and Mr. Meister who share voting and investment discretion with respect to the Shares held of record by CMLS Holdings LLC. C-LSH LLC and M-LSH LLC are the members of CMLS Holdings LLC, and Mr. Casdin is the managing member of C-LSH LLC. As such, each of the foregoing may be deemed to have or share beneficial ownership of the Shares held directly by CMLS Holdings LLC. Casdin Partners Master Fund, LP is the record holder of 3,007,164 Shares reported herein. Casdin Capital, LLC is the investment adviser to Casdin Partners Master Fund, LP and may be deemed to have or share beneficial ownership of the 3,007,164 Shares held by Casdin Partners Master Fund, LP. Casdin Partners GP, LLC is the general partner of Casdin Partners Master Fund LP and may be deemed to have or share beneficial ownership of the 3,007,164 Shares held by Casdin Partners Master Fund, LP, and Casdin Partners GP, LLC is also the direct beneficial owner of 19,247 Shares. Eli Casdin is the managing member of Casdin Capital, LLC and Casdin Partners GP, LLC. As such, each of the foregoing may be deemed to have or share beneficial ownership of the Shares held directly by Casdin Partners Master Fund, LP and Eli Casdin may be deemed the beneficial owner of the 19,247 Shares held by Casdin Partners GP, LLC. The Shares reflected as solely beneficially owned by Mr. Casdin also include 11,882 Shares issuable upon the exercise of fully vested options, 20,518 Shares that were issued upon the vesting of restricted stock units, and 3,576 Shares to be issued upon vesting of restricted stock units, in each case that were granted to Mr. Casdin in connection with his service on the board of directors of the Issuer. Keith Meister has the sole power to vote or to direct the vote and sole power to dispose or to direct the disposition of 34,912 Shares and shared power to vote or direct the vote and shared power to dispose or to direct the disposition of 3,595,914 Shares. The Shares reflected as beneficially owned by Mr. Meister include 333,144 Shares and 204,141 Shares issuable upon the exercise of 204,141 private placement warrants of the Issuer. On September 3, 2021, each private placement warrant became exercisable to purchase one Share at a price of $379.50 per share, subject to adjustment, as described in the definitive proxy statement of the Issuer (File No. 001-39482) filed with the SEC on July 2, 2021. CMLS Holdings LLC is the record holder of these Shares and warrants. The Board of Managers of CMLS Holdings LLC is comprised of Mr. Casdin and Mr. Meister who share voting and investment discretion with respect to the Shares held of record by CMLS Holdings LLC. C-LSH LLC and M-LSH LLC are the members of CMLS Holdings LLC, and Mr. Meister is the managing member of M-LSH LLC. As such, each of the foregoing may be deemed to have or share beneficial ownership of the Shares held directly by CMLS Holdings LLC. The Shares reflected as beneficially owned by Mr. Meister include 3,058,629 Shares owned by investment funds advised by Corvex Management LP, which may be deemed to be indirectly beneficially owned by Keith Meister by virtue of Mr. Meister's control of the general partner of Corvex Management LP. The Shares reflected as beneficially owned by Mr. Meister also include 11,207 Shares issuable upon the exercise of fully vested options, 20,129 Shares that were issued upon the vesting of restricted stock units, and 3,576 Shares to be issued upon vesting of restricted stock units, in each case that were granted to Mr. Meister in connection with his service on the board of directors of the Issuer.
(c)	The transactions by the Reporting Persons in the securities of the Issuer during the past sixty days are set forth in Exhibit B. All such transactions were carried out in open market transactions.
(d)	No person other than the Reporting Persons is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the Shares beneficially owned by the Reporting Persons.
(e)	Not applicable.
Item 7.	Material to be Filed as Exhibits.
	Exhibit A: Joint Filing Agreement Exhibit B: Schedule of Transactions in Shares

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.

CMLS Holdings LLC

Signature:	By: /s/ Eli Casdin
Name/Title:	Eli Casdin, Manager
Date:	08/26/2025

C-LSH LLC

Signature:	By: /s/ Eli Casdin
Name/Title:	Eli Casdin, Managing Member
Date:	08/26/2025

M-LSH LLC

Signature:	By: /s/ Keith A. Meister
Name/Title:	Keith A. Meister, Managing Member
Date:	08/26/2025

Casdin Capital, LLC

Signature:	By: /s/ Eli Casdin
Name/Title:	Eli Casdin, Managing Member
Date:	08/26/2025

Casdin Partners Master Fund, L.P.

Signature:	By: /s/ Eli Casdin
Name/Title:	Eli Casdin, Managing Member of its General Partner
Date:	08/26/2025

Casdin Partners GP, LLC

Signature:	By: /s/ Eli Casdin
Name/Title:	Eli Casdin, Managing Member
Date:	08/26/2025

Eli Casdin

Signature:	By: /s/ Eli Casdin
Name/Title:	Eli Casdin
Date:	08/26/2025

Keith A. Meister

Signature:	By: /s/ Keith A. Meister
Name/Title:	Keith A. Meister
Date:	08/26/2025

Corvex Management LP

Signature:	By: /s/ Keith A. Meister
Name/Title:	Keith Meister, Managing Partner
Date:	08/26/2025

Comments accompanying signature:

* This reporting person disclaims beneficial ownership of these reported securities except to the extent of its pecuniary interest therein, and this report shall not be deemed an admission that any such person is the beneficial owner of these securities for purposes of Section 16 of the U.S. Securities Exchange Act of 1934, as amended, or for any other purpose. Attention: Intentional misstatements or omissions of fact constitute Federal criminal violations (see 18 U.S.C. 1001).

FAQ

How many shares of GeneDx (WGS) does Eli Casdin beneficially own according to the Schedule 13D/A?

Eli Casdin is reported to beneficially own 3,599,671 shares, representing 12.4% of the Class A shares outstanding based on 28,726,248 shares.

What percentage of GeneDx (WGS) does Keith A. Meister beneficially own?

Keith A. Meister is reported to beneficially own 3,630,826 shares, representing 12.5% of the Class A shares outstanding.

Do the reported holdings include any warrants or options for GeneDx (WGS)?

Yes. The reported holdings include 204,141 private placement warrants exercisable at $379.50 per share and various fully vested options and restricted stock units disclosed in the filing.

What source of funds was used to purchase the shares reported in the filing?

The funds for the purchase of the shares listed in Exhibit B came from the working capital of Casdin Partners Master Fund, L.P. No borrowed funds were used to purchase the Shares other than ordinary working capital borrowings.

Are there recent transactions by the reporting persons in the last 60 days?

Yes. The filing states that transactions in the securities of the issuer during the past sixty days are set forth in Exhibit B, and that all such transactions were carried out in open market transactions.