DMTX Dimension Therapeutics, Inc.

Dimension Therapeutics, Inc. (NASDAQ:DMTX), a biopharmaceutical company advancing novel, adeno-associated virus (AAV) gene therapies targeting the liver, a key organ for human metabolism, today announced poster presentations that highlight technology underpinning select product candidate programs. The presentations will occur during the 20th ASGCT Annual Meeting, which is taking place in Washington, DC, May 10-13, 2017.

“We are pleased that the ASGCT will highlight novel approaches for manufacturing our AAV vectors, the early preclinical science supporting our clinical phase DTX301 program in OTC deficiency, and our translational collaboration with Jim Wilson, MD, PhD, professor of Medicine and Pediatrics at the Perelman School of Medicine at the University of Pennsylvania,” said Annalisa Jenkins, MBBS, FRCP, Chief Executive Officer of Dimension. “We remain committed to excelling in scientific innovation and R&D to address substantial patient needs in rare diseases associated with the liver.”

The presentation details are as follows:

Title: Rapid characterization of transient transfection conditions for scalable production of adeno-associated virus (AAV) using NanoSight NS300 (Abstract No. 713) Session Title: Vector and Cell Engineering and Manufacturing Session Date & Time: Friday, May 12, 2017, 5:45 PM - 7:45 PM Eastern Time Location: Exhibit Hall A & B South, Marriott Wardman Park Hotel, Washington, DC Authors: Jan T. Panteli, Linjing Li, Samantha Povlich, Anne Harris, Cameron Fulco, Chris Tipper, Reed Clark, Samuel Wadsworth, Ying Jing, Dimension Therapeutics, Cambridge, MA

Title: HeLa screening platform advancements to accelerate stable selection of high producing recombinant adeno-associated virus (rAAV) cell lines (Abstract No. 321) Session Title: AAV Vectors II Session Date & Time: Thursday, May 11, 2017, 5:15 PM-7:15 PM Eastern Time Location: Exhibit Hall A & B South, Marriott Wardman Park Hotel, Washington, DC Authors: Nicholas Richards, Alix Eastham, Vincent Borowy, Reed Clark, Sam Wadsworth, Ying Jing, Aubrey Tiernan, Dimension Therapeutics, Cambridge, MA

Title: Assessment of Biological Activity of DTX301 AAV Gene Therapy Product Using a Matrix Approach (Abstract No. 323) Session Title: AAV Vectors II Session Date & Time: Thursday, May 11, 2017, 5:15 PM - 7:15 PM, Eastern Time Location: Exhibit Hall A & B South, Marriott Wardman Park Hotel, Washington, DC Authors: Deborah Lebel‐Hagan1, Gwendolyn M. Wilmes2, Martin Lock1, Lili Wang1, Teresa L. Wright2, Lyndi Rice1, Christopher Cummings2, Gregg Wesolowski, Lorelei Stoica2, Shu‐Jen Chen1, William Zolla, Lisa M. Kattenhorn2, Reed Clark2, Samuel Wadsworth2, James M. Wilson1, 1Department of Medicine,University of Pennsylvania, Philadelphia, PA, USA, 2Dimension Therapeutics, Cambridge, MA, USA

Title: Long-term Rescue of a Hypomorphic Lethal Murine Model of Citrullinemia Type I by Liver-Directed, AAV8-Mediated Gene Therapy (Abstract No. 242) Poster Session Title: Novel Models for Genetic, Metabolic and Endocrine Disorders Session Date & Time: Wednesday, May 10, 2017, 5:30 PM - 7:30 PM, Eastern Time Location: Exhibit Hall A & B South, Marriott Wardman Park Hotel, Washington, DC Authors: Lili Wang1, John White2, Zhenning He2, Deirdre McMenamin2, James M. Wilson2Gene Therapy Program, 1Department of Pathology and Laboratory Medicine, 2Department of Medicine,University of Pennsylvania, Philadelphia, PA, USA

Title: AAV Gene Therapy for Phenylketonuria (Abstract No. 676)Oral Session Title: Metabolic, Storage, Endocrine, Liver and Gastrointestinal Diseases Date & Time: Friday, May 12, 2017, 5:45 PM - 7:45 PM, Eastern Time Location: Exhibit Hall A & B South, Marriott Wardman Park Hotel, Washington, DC Authors: Scott N. Ashley1, Jayme M. L. Nordin1, Christine Draper1, Jenny A. Greig1, James M. Wilson1 1Gene Therapy Program, Department of Medicine, University of Pennsylvania, Philadelphia, PA, USA

Editor's Note:  Dr. Wilson is a shareholder of Dimension and Dimension holds exclusive licenses and sublicenses (via REGENXBIO, Inc.) for certain Penn-owned AAV technologies related to these programs.

About Dimension Therapeutics, Inc.

Dimension Therapeutics, Inc. (NASDAQ:DMTX) is a leader in discovering and developing new therapeutic products for people living with devastating rare and metabolic diseases associated with the liver, based on the most advanced mammalian adeno-associated virus (AAV) gene delivery technology. Dimension is actively progressing its broad pipeline, which features programs addressing unmet needs for patients suffering from inherited metabolic diseases, including OTC deficiency, GSDIa, citrullinemia type 1, PKU, Wilson disease, a collaboration with Bayer in hemophilia A, and a wholly owned clinical program in hemophilia B. Dimension has two phase 1/2 clinical trials for the treatment of hemophilia B and OTC deficiency. The company targets diseases with readily identifiable patient populations, highly predictive preclinical models, and well-described, and often clinically validated, biomarkers. Founded in 2013, Dimension maintains headquarters in Cambridge, Massachusetts.

For more information, please visit www.dimensiontx.com.

Cautionary Note Regarding Forward-Looking Statements

This press release contains "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding the progress of Dimension’s portfolio and lead programs. All such forward-looking statements are based on management's current expectations of future events 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 the risks that Dimension’s product candidates, including its candidates, DTX101 and DTX301, will not successfully be developed or commercialized; and the risks described under the caption "Risk Factors" in Dimension Therapeutics’ Annual Report on Form 10-K for the year ended December 31, 2016, which is on file with the Securities and Exchange Commission, as well as other risks detailed in Dimension Therapeutics’ additional filings with the Securities and Exchange Commission. All information in this press release is as of the date of the release, and Dimension Therapeutics undertakes no duty to update this information unless required by law.

CONTACT:

Jean Franchi
Chief Financial Officer
Dimension Therapeutics
617-714-0709
jean.franchi@dimensiontx.com

Burns McClellan, on behalf of Dimension Therapeutics
Media: Justin Jackson
212-213-0006, ext.327
jjackson@burnsmc.com