What is the reported GeneDx (WGS) share count used for these ownership percentages?

The reported ownership percentages are calculated using 29,688,027 GeneDx Class A shares outstanding as of May 1, 2026. This share count comes from the company’s Form 10-Q filed with the SEC on May 4, 2026.

Casdin, Meister disclose sizable GeneDx (WGS) ownership positions

Filing Impact

(Moderate)

Filing Sentiment

(Neutral)

Form Type

SCHEDULE 13D/A

Rhea-AI Filing Summary

GeneDx Holdings Corp. received an updated Schedule 13D/A from investment groups associated with Eli Casdin and Keith Meister, detailing their ownership of the company’s Class A common stock. Based on 29,688,027 shares outstanding as of May 1, 2026, Eli Casdin reports beneficial ownership of 13.7% and Keith Meister reports 17.9%, including shares held through various funds, LLCs, warrants, options and restricted stock units. Corvex Management and Casdin Capital entities are also listed with double‑digit percentage stakes, reflecting significant institutional involvement in GeneDx.

Key Figures

Eli Casdin beneficial ownership: 4,099,671 shares (13.7%) Keith A. Meister beneficial ownership: 5,356,767 shares (17.9%) Corvex Management position: 4,784,570 shares (16.1%) +5 more

8 metrics

Eli Casdin beneficial ownership 4,099,671 shares (13.7%) Class A common stock based on 29,688,027 shares outstanding as of May 1, 2026

Keith A. Meister beneficial ownership 5,356,767 shares (17.9%) Class A common stock based on 29,688,027 shares outstanding as of May 1, 2026

Corvex Management position 4,784,570 shares (16.1%) Beneficial ownership of GeneDx Class A shares

Casdin Capital-related fund position 3,507,164 shares (11.8%) Casdin Partners Master Fund, L.P. holdings

CMLS Holdings LLC position 537,285 shares (1.8%) Beneficial ownership via CMLS Holdings LLC and related entities

Shares outstanding 29,688,027 shares GeneDx Class A shares outstanding as of May 1, 2026

Private placement warrant strike price $379.50 per share Exercise price for each private placement warrant exercisable into one share

Private placement warrants per principal holder 204,141 warrants Warrants held by each of Eli Casdin and Keith Meister

Key Terms

beneficial ownership, private placement warrants, restricted stock units, investment adviser, +1 more

5 terms

beneficial ownership financial

"Percent of class represented by amount in Row (11) 13.7 %"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

private placement warrants financial

"204,141 Shares issuable upon the exercise of 204,141 private placement warrants of the Issuer."

Private placement warrants are tradable coupons given directly to a limited group of investors that let the holder buy a company's shares at a fixed price before a set expiration date. They matter to investors because they can provide extra upside if the stock rises and give companies a way to raise money outside a public offering, but they also can increase the number of shares outstanding (dilution) and therefore affect share value and investor returns.

restricted stock units financial

"20,517 Shares that were issued upon the vesting of restricted stock units, and 3,576 Shares to be issued upon vesting of restricted stock units"

Restricted stock units are a type of company reward where employees are promised shares of stock, but they only fully own these shares after meeting certain conditions, like staying with the company for a set time. They matter because they can become valuable assets and are often used to motivate employees to help the company succeed.

investment adviser financial

"Casdin Capital, LLC is the investment adviser to Casdin Partners Master Fund, LP"

An investment adviser is a person or firm that professionally manages money and gives recommendations about buying, selling, or holding investments. Like a financial coach or guide, they have a legal duty to act in a client's best financial interest, so their advice, fees and potential conflicts can directly affect returns and risk — making their role important for investors who want informed, accountable help with portfolios.

general partner financial

"Casdin Partners GP, LLC is the general partner of Casdin Partners Master Fund LP"

A general partner is the person or firm that runs an investment partnership and legally represents it — they make the day-to-day decisions, choose which assets to buy or sell, and are responsible for the partnership’s obligations. Investors care because the general partner’s judgment, risk-taking and fee and profit-sharing arrangements determine both the potential returns and the level of exposure to losses; think of the GP as the ship’s captain whose skill and honesty shape the voyage’s outcome.

05/22/2026 - 05:20 PM

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 12)

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)

05/20/2026

(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

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, 6th Floor, Stamford, CONNECTICUT , 06902.

Item 1 Comment:

This Amendment No. 12 (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, May 7, 2025, and August 26, 2025, May 11, 2026 and May 15, 2026 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, as amended. 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 to the Schedule 13D is supplementally amended as follows, and Item 5 to the Schedule 13D is amended and restated 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 information set forth in Item 5(c) is hereby incorporated by reference into this Item 3. Such Shares reported as purchased in Item 5(c) were purchased with the working capital of investment funds advised by Casdin Capital, LLC.

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 29,688,027 Shares stated to be outstanding as of May 1, 2026, in the Issuer's Form 10-Q filed with the SEC on May 4, 2026. 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 4,063,696 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 3,507,164 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 3,507,164 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 3,507,164 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, 20,517 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 4,819,482 Shares and shared power to vote or direct the vote and shared power to dispose or to direct the disposition of 537,385 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 4,784,570 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 within 60 days, 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 Shares since the previous Schedule 13D are set forth in Exhibit 99.1 and such information is incorporated herein by reference. 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 99.1 - 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:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Manager
Date:	05/22/2026

C-LSH LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member
Date:	05/22/2026

M-LSH LLC

Signature:	/s/ Keith A. Meister
Name/Title:	Keith A. Meister / Managing Member
Date:	05/22/2026

Casdin Capital, LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member
Date:	05/22/2026

Casdin Partners Master Fund, L.P.

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member of Casdin Partners GP, LLC, its general partner
Date:	05/22/2026

Casdin Partners GP, LLC

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Managing Member
Date:	05/22/2026

Eli Casdin

Signature:	/s/ Eli Casdin
Name/Title:	Eli Casdin / Self
Date:	05/22/2026

Keith A. Meister

Signature:	/s/ Keith Meister
Name/Title:	Keith Meister / Self
Date:	05/22/2026

Corvex Management LP

Signature:	/s/ Keith Meister
Name/Title:	Keith Meister / Managing Partner
Date:	05/22/2026

Source: View Original Filing on SEC EDGAR

FAQ

What ownership stake does Eli Casdin report in GeneDx (WGS)?

Eli Casdin reports beneficial ownership of 4,099,671 GeneDx shares, or 13.7% of the Class A common stock. This figure includes direct holdings, fund-related positions, vested options, and restricted stock units tied to his board service.

How much GeneDx (WGS) stock does Keith A. Meister beneficially own?

Keith A. Meister reports beneficial ownership of 5,356,767 GeneDx shares, representing 17.9% of the Class A common stock. This includes shares held via Corvex-managed funds, interests through CMLS Holdings LLC, options, and restricted stock units granted for board service.

What position does Corvex Management report in GeneDx (WGS)?

Corvex Management reports beneficial ownership of 4,784,570 GeneDx Class A shares, equal to 16.1% of the outstanding stock. These shares are attributed to investment funds advised by Corvex and are indirectly associated with Keith Meister.

How many GeneDx (WGS) shares are tied to Casdin Capital-managed funds?

Casdin Partners Master Fund, L.P., advised by Casdin Capital, LLC, is the record holder of 3,507,164 GeneDx shares. Both Casdin Capital and its general partner Casdin Partners GP, LLC may be deemed to share beneficial ownership of these 3,507,164 shares.

What are the key warrant and equity award details disclosed for GeneDx (WGS)?

Both Eli Casdin and Keith Meister are reported to beneficially own 204,141 private placement warrants each, exercisable at $379.50 per GeneDx share. They also hold fully vested options and restricted stock units granted for service on GeneDx’s board of directors.