Class A common stock, $0.0001 par value per share

GENEDX HOLDINGS CORP.

333 Ludlow Street, Stamford, CT, 06902

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 28,533,204 Shares stated to be outstanding as of April 23, 2025 in the Issuer's Form 10-Q filed with the SEC on April 30, 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.

Eli Casdin has the sole power to vote or direct the vote and sole power to dispose or to direct the disposition of 32,399 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 Partners FO1-MSV LP is the record holder of 0 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, 7,593 Shares that were issued upon the vesting of restricted stock units, and 12,924 Shares to be issued upon vesting of restricted stock units within 60 days, 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 2,939,965 Shares and shared power to vote or direct the vote and shared power to dispose or to direct the disposition of 537,285 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 2,908,629 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, 7,205 Shares that were issued upon the vesting of restricted stock units, and 12,924 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.

The transactions by the Reporting Persons in the securities of the Issuer during the past sixty days are set forth in Exhibit 99.1. All such transactions were carried out in open market transactions.

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.

Not applicable.