AVROBIO, Inc. Reports Second Quarter 2018 Financial Results and Provides Business Update Completes IPO, initiates Phase 2 clinical trial in Fabry disease, expands board of directors CAMBRIDGE, MA.

AVROBIO, Inc. Reports Second Quarter 2018 Financial Results and Provides Business Update

Completes IPO, initiates Phase 2 clinical trial in Fabry disease, expands board of directors

CAMBRIDGE, MA., August 9, 2018 (GLOBE NEWSWIRE) AVROBIO, Inc. (NASDAQ:AVRO) (the Company ), a Phase 2 clinical stage gene

therapy company focused on developing potentially curative lentiviral-based gene therapies to treat rare diseases following a single dose, announced financial results for the second quarter 2018 and provided a business update.

2018 has been a very productive year thus far for AVROBIO, commented Geoff MacKay, President and Chief Executive Officer of AVROBIO. We

successfully completed a Series B financing and a successful initial public offering which positions us well to achieve our mission of advancing our pipeline of gene therapies to cure rare diseases in a single dose. Our main focus is on the

patients, and I am pleased with the progress we have made with our lead program, AVR-RD-01 in Fabry disease. In June, we completed the enrollment of the first patient in

our Phase 2 clinical trial, and even more recently, the third patient was enrolled in our ongoing investigator-sponsored Phase 1 clinical trial.

Second Quarter and Recent Business Highlights

Second Quarter Financial Results

AVROBIO reported a net

loss of $10.5 million for the second quarter 2018 as compared to $2.5 million for the prior year period. The increase in net loss for the year was due to increased research and development expenses, as well as an increase in general and

administrative expenses primarily related to investments in the Company s infrastructure in preparation for becoming a publicly traded company.

Research and development expenses for the second quarter 2018 were $7.4 million as compared to $1.9 million for the prior year period. The increase

in research and development expenses was primarily driven by increased spending on expenses and other costs used to advance AVROBIO s preclinical and clinical development activities for the Company s pipeline, as well as increased

personnel related costs due to the increase in employee headcount.

General and administrative expenses were $2.1 million for the second quarter 2018

as compared to $0.7 million for the prior year period. The increase in general and administrative expenses was primarily due to an increase in employee headcount, consulting and professional fees related to the preparation of the Company s

financial statements as well as support for ongoing business operations, and the impact of stock-based compensation in 2018.

AVROBIO ended the quarter with $155.0 million in cash and cash equivalents compared to

$6.0 million as of December 31, 2017. The increase was primarily the result of the completion of the Company s initial public offering, from which the Company received aggregate net proceeds of $104.2 million and the Series B

financing completed in January 2018 that generated net proceeds of $58.3 million.

Based on its current operating plan,

AVROBIO expects its cash and cash equivalents as of June 30, 2018, will enable it to fund its operating expenses and capital expenditure requirements into 2020.

AVROBIO, Inc., is a Phase 2 clinical

stage gene therapy company focused on developing potentially curative lentiviral-based gene therapies to treat rare diseases following a single dose. AVROBIO s gene therapies employ hematopoietic stem cells that are extracted from the patient

and then modified with lentiviral vectors to insert a functional copy of the gene that is defective in the target disease. AVROBIO is focused on the development of its 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.

AVROBIO is headquartered in Cambridge, MA and has offices in Toronto, ON. For additional information, visit www.avrobio.com.

Various express or implied statements in this release concerning AVROBIO s future expectations, plans and prospects, including without

limitation, its expectations regarding the contributions of any member of its board of directors, including such member s ability to affect AVROBIO s development or growth plans, statements regarding the development and the continued

progress of AVROBIO s programs, including the commencement of clinical trials or expansion of trial sites, and the therapeutic potential of its product candidates, and statements regarding the Company s cash position and expected runway,

constitute forward-looking statements for the purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. Any such statements in this press release that are not statements of historical fact may be deemed to be

forward-looking statements. Any forward-looking statements in this press release are based on management s current expectations of future events only as of today 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, the risk that any one or more of AVROBIO s product candidates will

not be successfully developed or commercialized, the risk of cessation or delay of any of AVROBIO s ongoing or planned clinical trials, and the risk that the results of previously conducted studies will not be repeated or observed in ongoing or

future studies involving AVROBIO s product candidates. 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 from those contained in the

forward-looking statements, see the section entitled Risk Factors in the final prospectus related to AVROBIO s initial public offering filed with the Securities and Exchange Commission pursuant to Rule 424(b) of the Securities Act

of 1933, as amended, as well as discussions of potential risks, uncertainties and other important factors in AVROBIO s subsequent filings with the Securities and Exchange Commission. AVROBIO explicitly disclaims any obligation to update any

forward-looking statements except to the extent required by law.

Christopher F. Brinzey

CONDENSED CONSOLIDATED BALANCE SHEETS

(In thousands, except share data)

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except share and per share data)