AVROBIO, Inc. Reports Fourth Quarter and Fiscal Year 2018 Financial Results and Provides Business Update Recruitment completed in investigator-sponsored Phase 1 Fabry study Phase 1 and Phase 2 clinical data updates for A

AVROBIO, Inc. Reports Fourth Quarter and Fiscal Year 2018 Financial Results and Provides Business Update

Recruitment completed in investigator-sponsored Phase 1 Fabry study

Phase 1 and Phase 2 clinical data updates for AVR-RD-01 in

Fabry disease reported at WORLDSymposium 2019

Clinical trials in Gaucher and cystinosis expected to start in 2019

Introduced platoTM platform for worldwide gene therapy commercialization, to be

incorporated in AVROBIO-sponsored clinical trials in 2019

CAMBRIDGE, Mass., March 25, 2019 AVROBIO, Inc. (NASDAQ: AVRO) (the

Company ), a Phase 2 clinical-stage gene therapy company, today reported financial results for the fourth quarter and fiscal year ended December 31, 2018 and provided a business update.

2018 was a very productive year for AVROBIO, as we built a solid financial foundation with our IPO and made significant progress advancing our pipeline

of gene therapies for Fabry and other lysosomal storage diseases, commented Geoff MacKay, President and Chief Executive Officer of AVROBIO. We enter 2019 with strong momentum. Our recently-presented preliminary clinical data from the

Fabry program builds upon a growing body of evidence for the therapeutic potential of AVR-RD-01 as a gene therapy for patients with this debilitating disease. In

addition, we look forward to expanding AVROBIO s clinical activities, with trials for Gaucher disease and cystinosis expected to start in 2019. Finally, after three and a half years of development, we were excited to introduce the platoTM platform, which includes a proprietary vector system, cell manufacturing solution and conditioning regimen with therapeutic drug monitoring. We believe that plato provides the foundation for the

potential worldwide commercialization of our gene therapies. We plan to incorporate plato into our Fabry and Gaucher clinical trials in the second half of 2019.

Fourth Quarter and Recent Business Highlights

The Company intends to start using plato in its

FAB-201 and GAU-201 clinical trials in 2019.

Fourth Quarter and Fiscal Year 2018 Financial Results

AVROBIO reported a net loss of $16.0 million for the fourth quarter of 2018, and a net loss of $46.4 million for the year ended

December 31, 2018, as compared to a net loss of $7.6 million and a net loss of $18.6 million for the comparable periods in 2017, respectively. These increases were due to increased research and development expenses, as well as

increased general and administrative expenses.

Research and development expenses were $12.8 million for the fourth quarter of 2018, and

$35.1 million for the year ended December 31, 2018, as compared to $6.5 million and $15.2 million for the comparable periods in 2017, respectively. These increases were driven by increased preclinical and clinical development

activities related to the advancement of the Company s pipeline, as well as increased personnel-related costs resulting from an increase in employee headcount.

General and administrative expenses were $3.9 million for the fourth quarter of 2018, and $11.1 million for the year ended December 31, 2018,

as compared to $1.0 million and $3.2 million for the comparable periods in 2017, respectively. These increases were primarily due to an increase in employee headcount, consulting and professional fees related to the support of ongoing

business operations as a publicly traded company, and the impact of stock-based compensation.

As of December 31, 2018,

AVROBIO had $126.3 million in cash and cash equivalents, as compared to $6.0 million in cash and cash equivalents as of December 31, 2017. This increase was primarily the result of the completion of the Company s initial public

offering completed in June 2018, which raised net proceeds of $104.0 million, and the Company s Series B financing completed in January 2018, which generated net proceeds of $58.3 million. Based on the Company s current

operating plan, AVROBIO expects its cash and cash equivalents as of December 31, 2018 will enable the Company to fund its operating expenses and capital expenditure requirements into the second half of 2020.

AVROBIO, Inc., is a Phase 2

clinical-stage gene therapy company developing gene therapies to potentially cure rare diseases with a single dose. AVROBIO s lentiviral-based gene therapies employ hematopoietic stem cells that are collected from the patient and then modified

with a lentiviral vector to insert functional copies 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. The Company s plato platform is a proprietary vector system and automated, closed cell manufacturing solution designed to support worldwide commercialization.

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

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 our business strategy, prospective products and goals, the therapeutic potential of our product candidates, the design, commencement,

enrollment and timing of ongoing or planned clinical trials, clinical trial results, product approvals and regulatory pathways, the intended incentives conferred by orphan drug designation, potential regulatory approvals and the timing thereof,

anticipated benefits of our gene therapy platform including potential impact on our commercialization activities, timing and likelihood of success, plans and objectives of management for future operations, future results of anticipated products, and

the market opportunity for our product candidates, and statements regarding the Company s financial and cash position and expected cash runway. 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 about our industry as well as management s current beliefs and 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 ongoing or planned clinical trials of AVROBIO or our collaborators, the risk that AVROBIO may not realize the intended benefits of our gene therapy platform, including the features of our

plato platform, the risk that our product candidates or procedures in connection with the administration thereof will not have the safety or efficacy profile that we anticipate, the risk that prior results, such as signals of safety, activity or

durability of effect, observed from preclinical or clinical trials, will not be replicated or will not continue in ongoing or future studies or trials involving AVROBIO s product candidates, the risk that we will be unable to obtain and

maintain regulatory approval for our product candidates, the risk that the size and growth potential of the market for our product candidates will not materialize as expected, risks associated with our dependence on third-party suppliers and

manufacturers, risks regarding the accuracy of our estimates of expenses and future revenue, risks relating to our capital requirements and needs for additional financing, and risks relating to our ability to obtain and maintain intellectual

property protection for our 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 materially and adversely from those contained

in the forward-looking statements, see the section entitled Risk Factors in AVROBIO s Quarterly Report on Form 10-Q for the quarter ended September 30, 2018, 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

Christopher F. Brinzey

Westwicke, and ICR Company

CONDENSED CONSOLIDATED BALANCE SHEETS

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except share and per share data)