# EDGAR Filing Document

**Accession Number:** 0001822257
**File Stem:** 0000919574-26-003685
**Filing Date:** 2026-5
**Character Count:** 32053
**Document Hash:** 63a9d8cbbf19c8b9b731a8885626c910
**Contains OCR:** False
**Source Format:** 

## Filing Content

## Filing Summary
**0000919574-26-003685.hdr.sgml**: 20260522

**ACCESSION NUMBER**: 0000919574-26-003685

**CONFORMED SUBMISSION TYPE**: SCHEDULE 13D/A

**PUBLIC DOCUMENT COUNT**: 2

**FILED AS OF DATE**: 20260522

**DATE AS OF CHANGE**: 20260522

**SUBJECT COMPANY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** GeneDx Holdings Corp.
- **CENTRAL INDEX KEY:** 0001818331
- **STANDARD INDUSTRIAL CLASSIFICATION:** SERVICES-HEALTH SERVICES [8000]
- **ORGANIZATION NAME:** 08 Industrial Applications and Services
- **EIN:** 851966622
- **STATE OF INCORPORATION:** DE
- **FISCAL YEAR END:** 1231

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A
- **SEC ACT:** 1934 Act
- **SEC FILE NUMBER:** 005-91664
- **FILM NUMBER:** 261015093

**BUSINESS ADDRESS:**
- **STREET 1:** 333 LUDLOW STREET
- **STREET 2:** NORTH TOWER, 6TH FLOOR
- **CITY:** STAMFORD
- **STATE:** CT
- **ZIP:** 06902
- **BUSINESS PHONE:** 888-729-1206

**MAIL ADDRESS:**
- **STREET 1:** 333 LUDLOW STREET
- **STREET 2:** NORTH TOWER, 6TH FLOOR
- **CITY:** STAMFORD
- **STATE:** CT
- **ZIP:** 06902

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** Sema4 Holdings Corp.
- **DATE OF NAME CHANGE:** 20210721

**FORMER COMPANY:**
- **FORMER CONFORMED NAME:** CM Life Sciences, Inc.
- **DATE OF NAME CHANGE:** 20200715
**FILED BY**: 

**COMPANY DATA:**
- **COMPANY CONFORMED NAME:** CMLS Holdings LLC
- **CENTRAL INDEX KEY:** 0001822257

**ORGANIZATION NAME:**
- **EIN:** 851989037

**FILING VALUES:**
- **FORM TYPE:** SCHEDULE 13D/A

**BUSINESS ADDRESS:**
- **STREET 1:** C/O CORVEX MANAGEMENT LP
- **STREET 2:** 667 MADISON AVENUE
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10065
- **BUSINESS PHONE:** 212 474 6745

**MAIL ADDRESS:**
- **STREET 1:** C/O CORVEX MANAGEMENT LP
- **STREET 2:** 667 MADISON AVENUE
- **CITY:** NEW YORK
- **STATE:** NY
- **ZIP:** 10065

## Exhibit 99.1

Exhibit 99.1

**Schedule of Transactions in Shares**

---

| | | | | |
|:---|:---|:---|:---|:---|
| &nbsp;&nbsp; <br> <u>Date of Transaction</u> | &nbsp;&nbsp; <br> <u>Reporting Person</u> | &nbsp;&nbsp; <br> <u>Title of Class</u> | &nbsp;&nbsp; <br> <u>Number of Shares Acquired (Disposed)</u> | &nbsp;&nbsp; <br> <u>Price Per</u> <br> <u>Share (1)</u><br>|
| &nbsp;&nbsp;05/18/2026 | &nbsp;&nbsp;Casdin Partners Master Fund, L.P. | &nbsp;&nbsp;Class A Common Stock, par value $0.0001 per share | &nbsp;&nbsp; 175000 | &nbsp;&nbsp;$42.5517 (1) |
| &nbsp;&nbsp;05/19/2026 | &nbsp;&nbsp;Casdin Partners Master Fund, L.P. | &nbsp;&nbsp;Class A Common Stock, par value $0.0001 per share | &nbsp;&nbsp; 185000 | &nbsp;&nbsp;$42.5964 (2) |
| &nbsp;&nbsp;05/20/2026 | &nbsp;&nbsp;Casdin Partners Master Fund, L.P. | &nbsp;&nbsp;Class A Common Stock, par value $0.0001 per share | &nbsp;&nbsp; 140000 | &nbsp;&nbsp;$43.8061 (3) |

---

(1) The price reported is a weighted average price. These shares were bought in multiple transactions within the range of $42.4573 to $42.9153. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares bought at each separate price within the range set forth in this footnote.

(2) The price reported is a weighted average price. These shares were bought in multiple transactions within the range of $42.1118 to $42.6898. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares bought at each separate price within the range set forth in this footnote.

(3) The price reported is a weighted average price. These shares were bought in multiple transactions within the range of $43.6287 to $44.3384. The Reporting Persons undertake to provide to the Issuer, any security holder of the Issuer or the staff of the Securities and Exchange Commission, upon request, full information regarding the number of shares bought at each separate price within the range set forth in this footnote.

### UNITED STATES 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)*

**—**

*(CUSIP Number)*

**Eli Casdin and Keith Meister**<br>c/o Corvex Management LP<br>667 Madison Avenue<br>New York NY 10065<br>(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)*

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**CMLS Holdings LLC** | Name of reporting person<br>**CMLS Holdings LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**OO** | Source of funds (See Instructions)<br>**OO** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**537285.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**537285.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**537285.00** | Aggregate amount beneficially owned by each reporting person<br>**537285.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**1.8%** | Percent of class represented by amount in Row (11)<br>**1.8%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**C-LSH LLC** | Name of reporting person<br>**C-LSH LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**OO** | Source of funds (See Instructions)<br>**OO** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**537285.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**537285.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**537285.00** | Aggregate amount beneficially owned by each reporting person<br>**537285.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**1.8%** | Percent of class represented by amount in Row (11)<br>**1.8%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**HC** | Type of Reporting Person (See Instructions)<br>**HC** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**M-LSH LLC** | Name of reporting person<br>**M-LSH LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**OO** | Source of funds (See Instructions)<br>**OO** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**537285.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**537285.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**537285.00** | Aggregate amount beneficially owned by each reporting person<br>**537285.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**1.8%** | Percent of class represented by amount in Row (11)<br>**1.8%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**HC** | Type of Reporting Person (See Instructions)<br>**HC** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Casdin Capital, LLC** | Name of reporting person<br>**Casdin Capital, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**3507164.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**3507164.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**3507164.00** | Aggregate amount beneficially owned by each reporting person<br>**3507164.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**11.8%** | Percent of class represented by amount in Row (11)<br>**11.8%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IA** | Type of Reporting Person (See Instructions)<br>**IA** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Casdin Partners Master Fund, L.P.** | Name of reporting person<br>**Casdin Partners Master Fund, L.P.** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**WC** | Source of funds (See Instructions)<br>**WC** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**CAYMAN ISLANDS** | Citizenship or place of organization<br>**CAYMAN ISLANDS** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**3507164.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**3507164.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**3507164.00** | Aggregate amount beneficially owned by each reporting person<br>**3507164.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**11.8%** | Percent of class represented by amount in Row (11)<br>**11.8%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**PN** | Type of Reporting Person (See Instructions)<br>**PN** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Casdin Partners GP, LLC** | Name of reporting person<br>**Casdin Partners GP, LLC** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**3526411.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**3526411.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**3526411.00** | Aggregate amount beneficially owned by each reporting person<br>**3526411.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**11.9%** | Percent of class represented by amount in Row (11)<br>**11.9%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**OO** | Type of Reporting Person (See Instructions)<br>**OO** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Eli Casdin** | Name of reporting person<br>**Eli Casdin** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**35975.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**4063696.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**35975.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**4063696.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**4099671.00** | Aggregate amount beneficially owned by each reporting person<br>**4099671.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**13.7%** | Percent of class represented by amount in Row (11)<br>**13.7%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Keith A. Meister** | Name of reporting person<br>**Keith A. Meister** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**OO** | Source of funds (See Instructions)<br>**OO** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[ ] | |
| 6 | Citizenship or place of organization<br>**X1** | Citizenship or place of organization<br>**X1** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**4819482.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**537285.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**4819482.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**537285.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**5356767.00** | Aggregate amount beneficially owned by each reporting person<br>**5356767.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**17.9%** | Percent of class represented by amount in Row (11)<br>**17.9%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IN** | Type of Reporting Person (See Instructions)<br>**IN** | |

---

| **CUSIP No.** | **—** |

---

| | | | |
|:--|:--|:--|:--|
| 1 | Name of reporting person<br>**Corvex Management LP** | Name of reporting person<br>**Corvex Management LP** | |
| 2 | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | Check the appropriate box if a member of a Group (See Instructions)<br>[x] (a)<br>[ ] (b) | |
| 3 | SEC use only | SEC use only | |
| 4 | Source of funds (See Instructions)<br>**AF** | Source of funds (See Instructions)<br>**AF** | |
| 5 | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[x] | Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)<br>[x] | |
| 6 | Citizenship or place of organization<br>**DELAWARE** | Citizenship or place of organization<br>**DELAWARE** | |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 7 | Sole Voting Power<br>**4784570.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 8 | Shared Voting Power<br>**0.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 9 | Sole Dispositive Power<br>**4784570.00** |
| Number of Shares<br>Beneficially Owned by<br>Each Reporting Person With: | 10 | Shared Dispositive Power<br>**0.00** |
| 11 | Aggregate amount beneficially owned by each reporting person<br>**4784570.00** | Aggregate amount beneficially owned by each reporting person<br>**4784570.00** | |
| 12 | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)<br>[ ] | |
| 13 | Percent of class represented by amount in Row (11)<br>**16.1%** | Percent of class represented by amount in Row (11)<br>**16.1%** | |
| 14 | Type of Reporting Person (See Instructions)<br>**IA** | Type of Reporting Person (See Instructions)<br>**IA** | |

---

**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, CT, 06902

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 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.

### 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.

**Reporting Person:** CMLS Holdings LLC

**Signature:** /s/ Eli Casdin

**Name/Title:** Eli Casdin / Manager

**Date:** 05/22/2026

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.

**Reporting Person:** C-LSH LLC

**Signature:** /s/ Eli Casdin

**Name/Title:** Eli Casdin / Managing Member

**Date:** 05/22/2026

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.

**Reporting Person:** M-LSH LLC

**Signature:** /s/ Keith A. Meister

**Name/Title:** Keith A. Meister / Managing Member

**Date:** 05/22/2026

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.

**Reporting Person:** Casdin Capital, LLC

**Signature:** /s/ Eli Casdin

**Name/Title:** Eli Casdin / Managing Member

**Date:** 05/22/2026

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.

**Reporting Person:** 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

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.

**Reporting Person:** Casdin Partners GP, LLC

**Signature:** /s/ Eli Casdin

**Name/Title:** Eli Casdin / Managing Member

**Date:** 05/22/2026

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.

**Reporting Person:** Eli Casdin

**Signature:** /s/ Eli Casdin

**Name/Title:** Eli Casdin / Self

**Date:** 05/22/2026

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.

**Reporting Person:** Keith A. Meister

**Signature:** /s/ Keith Meister

**Name/Title:** Keith Meister / Self

**Date:** 05/22/2026

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.

**Reporting Person:** Corvex Management LP

**Signature:** /s/ Keith Meister

**Name/Title:** Keith Meister / Managing Partner

**Date:** 05/22/2026