Amendment: SEC Form SCHEDULE 13D/A filed by GeneDx Holdings Corp.

Item 3 of the Schedule 13D is hereby amended and supplemented as follows: The information set forth in Item 4 of this Amendment No. 6 is hereby incorporated by reference into this Item 3.

Item 4 is hereby amended and supplemented as follows: On January 30, 2025, ISMMS sold 200,000 shares of Class A Common Stock at a price of $78.50 per share. On February 13, 2025, ISMMS sold 400,000 shares of Class A Common Stock at a price of $77.5776 per share, on February 14, 2025, ISMMS sold 89,676 shares of Class A Common Stock at a price of $76.9296 per share, and on February 18, 2025, ISMMS sold 350,000 shares of Class A Common Stock at a price of $100.4069 per share. Each sale was made in reliance on Rule 144 promulgated under the Securities Act of 1933. ISMMS previously filed a Form 144 on January 30, 2025, disclosing ISMMS's intention to sell up to 1,346,123 shares of Class A Common Stock within the next 90 days, which amount includes the aggregate 1,039,676 shares sold as described above. The information in Item 3 of the Schedule 13D is incorporated by reference into this Item 4. The Reporting Persons expect to evaluate on an ongoing basis the Issuer's financial condition and prospects and their respective interests in, and intentions with respect to, the Issuer and their respective investments in the securities of the Issuer, which review may be based on various factors, including the Issuer's business and financial condition, results of operations and prospects, general economic and industry conditions, the securities markets in general and those for the Issuer's securities in particular, as well as other developments and other investment opportunities. Accordingly, each Reporting Person reserves the right to change its intentions, as it deems appropriate. In particular, each Reporting Person may, at any time and from time to time, in the open market, in privately negotiated transactions or otherwise, increase its holdings in the Issuer or dispose of all or a portion of the securities of the Issuer that such Reporting Person now owns or may hereafter acquire, including sales pursuant to the exercise of the registration rights provided for in the Subscription Agreements or in the Registration Rights Agreement described in the Schedule 13D. Except as described in the Schedule 13D, the Reporting Persons do not have any present plans or proposals that relate to or would result in any of the actions described in subparagraphs (a) through (j) of Item 4 of Schedule 13D, although, subject to the agreements described herein, the Reporting Persons, at any time and from time to time, may review, reconsider and change their position and/or change their purpose and/or develop such plans and may seek to influence management or the board of the Issuer with respect to the business and affairs of the Issuer and may from time to time consider pursuing or proposing such matters with advisors, the Issuer or other persons.

Item 5 of the Schedule 13D is hereby amended and restated as follows: (a) and (b) Items 7 through 11 and 13 of each of the cover pages of this Amendment No. 6 are incorporated herein by reference. Calculation of the percentage of shares of Class A Common Stock beneficially owned assumes that there were 27,471,397 shares of Class A Common Stock issued and outstanding. As of February 18, 2025, after the disposition as described above, ISMMS directly owns 1,680,016 shares of Class A Common Stock. The information set forth in Item 4 of this Amendment No. 6 is hereby incorporated by reference into this Item 5. MSHS disclaims beneficial ownership over all shares beneficially owned by ISMMS, other than for the purpose of determining obligations under the Securities Exchange Act of 1934, as amended, and the filing of this Amendment No. 6 shall not be deemed an admission that MSHS is the beneficial owner of such securities for any other purpose.

Except as described in Item 4 of this Amendment No. 6, which is incorporated herein by reference, since the most recent filing of Schedule 13D, none of the Reporting Persons conducted transactions in the Class A Common Stock.

To the knowledge of the Reporting Persons, no one other than the Reporting Persons has the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities of the Issuer reported as beneficially owned by the Reporting Persons herein.

Not applicable.

Item 6 of the Schedule 13D is hereby amended and restated as follows: The information set forth in Items 2, 3, 4 and 5 is hereby incorporated by reference into this Item 6. The Subscription Agreements described in Amendment No. 1 provide for certain customary registration rights for the PIPE investors. The Registration Rights Agreement described in the Initial Filing provides for certain customary registration rights for certain shareholders of the Issuer.

Item 7 of this Amendment No. 6 incorporates herein by reference the information set forth in Item 7 of the Schedule 13D.