AVROBIO Reports Fourth Quarter and Fiscal Year 2019 Financial Results and Provides Business Update Presented positive data at the 16 th Annual WORLDSymposium on AVR-RD-04 for cystinosis and AVR-RD-01 for Fabry disease, a

AVROBIO Reports Fourth Quarter and Fiscal Year 2019 Financial Results and Provides Business Update

Presented positive data at the 16th Annual WORLDSymposium on AVR-RD-04 for cystinosis and

AVR-RD-01 for Fabry disease, as well as early data on plato -produced drug product and

plasma enzyme activity level

Received orphan drug designation from U.S. Food and Drug Administration for

AVROBIO investigational gene

therapy to receive orphan status

Raised $100 million in gross proceeds from follow-on

common stock offering in February 2020,

extending cash runway into Q2 2022

CAMBRIDGE, Mass., March 16, 2020 AVROBIO, Inc. (Nasdaq: AVRO), a leading clinical-stage gene therapy company with a mission to free

people from a lifetime of genetic disease, today reported financial results for the fourth quarter and year ended Dec. 31, 2019 and provided a business update.

For AVROBIO, 2019 was an important year, with positive data on a primary clinical endpoint from the first patient in our Fabry Phase 2 trial and the

unveiling of our state-of-the-art gene therapy

platform, plato , said Geoff MacKay, AVROBIO s president and CEO. This momentum has put us in a strong position for 2020. Our presence at WORLDSymposium in February included sharing supportive initial data for cystinosis and plato-produced drug product, as well as further data supporting efficacy and durability in Fabry disease, with our first

Phase 1 patient now out to 32 months. We believe 2020 will be our breakout year, with important updates across our pipeline of investigational single-dose treatments for lysosomal disorders as well as our early-stage portfolio.

Program Updates and Milestones

AVR-RD-01 in Fabry disease: Evidence of durability and tolerability across both Phase 1 and Phase 2 trials

AVROBIO has two investigational gene therapy clinical trials for Fabry disease. Four patients have been dosed in the Phase 2 trial (FAB-201) and five patients have been dosed in the Phase 1 investigator-led trial of AVR-RD-01.

Across both studies:

AVR-RD-01 Phase 1 trial in Fabry disease: Interim data continue to

support potential first-line use

AVR-RD-01 Phase 2 trial in

Fabry disease: Interim data support potential first line use

trial in cystinosis: Three-month data from first patient suggest positive trends across multiple measures

AVR-RD-02 Phase 1/2 trial in Gaucher disease: Expect to dose first

plato gene therapy platform debut: Presented one-month data for fourth patient in Phase 2

Fabry trial (FAB-201)

Strengthened balance sheet and extended anticipated cash runway into Q2 2022

Fourth Quarter and Fiscal Year 2019 Financial Results

AVROBIO reported a net loss of $22.7 million for the fourth quarter of 2019, and a net loss of $73.0 million for the year ended 2019, as compared to

a net loss of $16.0 million and a net loss of $46.4 million for the comparable periods in 2018, respectively. These increases were due to increased research and development expenses, as well as increased general and administrative

Research and development expenses were $17.2 million for the fourth quarter of 2019, and $55.0 million for the year ended 2019, as

compared to $12.8 million and $35.1 million for the comparable periods in 2018, respectively. These increases were driven by increased program 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. Also, during the fourth quarter of 2019, the company made a milestone payment of $2.0 million to GenStem Therapeutics, Inc., in connection with the dosing of

the first patient in the Phase 1/2 clinical trial of AVR-RD-04 in cystinosis in the United States.

General and administrative expenses were $6.2 million for the fourth quarter of 2019, and $20.8 million for the year ended 2019, as compared to

$3.9 million and $11.1 million for the comparable periods in 2018, respectively. These increases were primarily due to an increase in employee headcount, expenses associated with being a publicly traded company and the impact of non-cash stock-based compensation.

As of Dec. 31, 2019, AVROBIO had $187.0 million in cash

and cash equivalents, as compared to $126.3 million in cash and cash equivalents as of Dec. 31, 2018. This increase was primarily the result of the completion of the company s follow-on common stock

offering completed in July 2019, which raised net proceeds of $129.5 million. Based on the company s current operating plan, AVROBIO expects its cash and cash equivalents as of Dec. 31, 2019, together with the net proceeds from the

February 2020 follow-on common stock offering, will enable the company to fund its operating expenses and capital expenditure requirements into Q2 2022.

Our mission is to free people from a lifetime of genetic disease with a single dose of gene therapy. We aim to halt or reverse disease throughout the body by

driving durable expression of functional protein, even in hard-to-reach tissues and organs including the brain, muscle and bone. Our clinical-stage programs include

Fabry disease, Gaucher disease and cystinosis and we also are advancing a program in Pompe disease. AVROBIO is powered by the plato gene therapy platform, our foundation designed to

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 and phrases such as aims,

anticipates, believes, could, designed to, estimates, expects, forecasts, goal, intends, may, plans,

possible, potential, seeks, will, and variations of these words and phrases or similar expressions that are intended to identify forward-looking statements. These forward-looking statements include,

without limitation, statements regarding our business strategy for and the potential therapeutic benefits of our prospective product candidates, the design, commencement, enrollment and timing of ongoing or planned clinical trials, clinical trial

results, product approvals and regulatory pathways, anticipated benefits of our gene therapy platform including potential impact on our commercialization activities, timing and likelihood of success, the expected benefits and results of our

implementation of the plato platform in our clinical trials and gene therapy programs, the expected safety profile of our investigational gene therapies, and statements regarding our 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.

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 successfully recruit or enroll a sufficient number of patients for our clinical trials, 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, risks relating to business interruptions resulting from the coronavirus disease (COVID-19) outbreak or similar public health crises, 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 most recent Annual or Quarterly Report, 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

Westwicke, an ICR Company

Ten Bridge Communications

CONDENSED CONSOLIDATED BALANCE SHEETS

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS

(In thousands, except share and per share data)