AVROBIO Announces Proposed Public Offering of Common Stock CAMBRIDGE, Mass .

AVROBIO Announces Proposed Public Offering of Common Stock

CAMBRIDGE, Mass. July 16, 2019 AVROBIO, Inc. (NASDAQ: AVRO) (the Company ), a Phase 2 clinical-stage gene therapy

company, today announced that it intends to offer and sell, subject to market and other conditions, $100.0 million of its common stock in an underwritten public offering. The Company expects to grant the underwriters a 30-day option to purchase up to $15.0 million of additional shares of its common stock (15%) offered in the public offering. All of the shares in the proposed offering are to be sold by the Company. The

offering is subject to market and other conditions, and there can be no assurance as to whether or when the offering may be completed, or as to the actual size or terms of the offering.

Morgan Stanley and Cowen are acting as joint book-running managers for the offering.

The Company intends to use the net proceeds from the offering, in addition to its existing cash resources, to fund the support of the Company s current

programs in Fabry disease, Gaucher disease, cystinosis and Pompe disease, fund external and internal manufacturing and process development activities related to the Company s programs and to fund research and development activities that relate

to all of the Company s clinical and preclinical activities, including the cost of research and development personnel, and the remainder for planned general and administrative expenses, working capital and other general corporate purposes.

The securities described may be offered pursuant to a shelf registration statement on Form S-3 (File No. 333-232489), including a base prospectus. The securities may be offered only by means of a prospectus. A preliminary prospectus supplement related to the offering and a final prospectus supplement related

to the offering will be filed with the U.S. Securities and Exchange Commission (SEC) and will be available on the SEC s website at www.sec.gov. Copies of the preliminary prospectus supplement and the accompanying prospectus relating to the

securities being offered may also be obtained by contacting: Morgan Stanley & Co. LLC, Attention: Prospectus Department, 180 Varick Street, 2nd Floor, New York, NY 10014 or Cowen and

Company, LLC, Attention: Prospectus Department, c/o Broadridge Financial Solutions, 1155 Long Island Avenue, Edgewood, NY 11717, by telephone at (631) 274-2806.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy these securities, nor shall there be any sale of these

securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

AVROBIO, Inc., is a Phase 2

clinical-stage gene therapy company. AVROBIO is focused on the development of its investigational gene therapy, AVR-RD-01, in Fabry disease, as well as additional gene

therapy programs in other lysosomal storage disorders including Gaucher disease, cystinosis and Pompe disease.

Forward-Looking Statements

This press release contains forward-looking statements, including statements made pursuant to the safe harbor provisions of the Private Securities Litigation

Reform Act of 1995. These statements may be identified by words such as aims, anticipates, believes, could, estimates, expects, forecasts, goal,

intends, may, plans, possible, potential, seeks, will, and variations of these words or similar expressions that are intended to identify forward-looking statements.

These forward-looking statements include, without limitation, statements regarding completion, timing and anticipated size of the proposed offering and the anticipated use of proceeds therefrom. Any such statements in this press release that are not

statements of historical fact may be deemed to be forward-looking statements. Results in preclinical or early stage clinical trials may not be indicative of results from later stage or larger scale clinical trials and do not ensure regulatory

approval. You should not place undue reliance on these statements, or the scientific data presented.

Any forward-looking statements in this press release

are based on AVROBIO s current expectations, estimates and projections only as of the date of this release and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set

forth in or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to, completion of the proposed public offering on the anticipated terms, or at all, market conditions and the satisfaction of

customary closing conditions related to the proposed public offering. For a discussion of these and other risks and uncertainties, and other important factors, any of which could cause AVROBIO s actual results to differ materially and adversely

from those contained in the forward-looking statements, see the section entitled Risk Factors in AVROBIO s Annual Report on Form 10-K for the fiscal year ended December 31, 2018 and our

subsequent periodic reports on Form 10-Q, as well as discussions of potential risks, uncertainties, and other important factors in our other filings with the SEC, including those contained or incorporated by

reference in the preliminary prospectus supplement related to the proposed public offering to be filed with the SEC. AVROBIO explicitly disclaims any obligation to update any forward-looking statements except to the extent required by law.

Christopher F. Brinzey