Bain Capital Life Sciences Entities' Ownership in X4 Pharmaceuticals, Inc.

Bain Capital Life Sciences Fund, L.P., Bain Capital Life Sciences Fund II, L.P., BCIP Life Sciences Associates, LP, BCLS II Investco, LP, BCLS I Investco, LP, and BCLS II Equity Opportunities, LP (collectively, the 'Reporting Persons') have filed a Schedule 13G to report their collective beneficial ownership of 9.99% of the outstanding shares of Common Stock of X4 Pharmaceuticals, Inc. As of the date of the filing, the Reporting Persons hold a total of 2,436,588 shares of Common Stock, including shares issuable upon the exercise of warrants and pre-funded warrants, subject to certain beneficial ownership blockers. The Reporting Persons are prohibited from exercising warrants or pre-funded warrants if such exercise would result in their beneficial ownership exceeding 9.99% of the total number of shares of Common Stock then issued and outstanding. The filing is made pursuant to Rule 13d-1(c) of the Securities Exchange Act of 1934.