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Homology Medicines Announces Peer-Reviewed Publication of Five-Year Retrospective Study Conducted in Collaboration with Two PKU Key Opinion Leaders Demonstrating Substantially Elevated Phe Levels in Adults with Classical PKU on Standard of Care

- These Data Highlight Unmet Medical Need for Therapies to Control Phe Concentrations by Targeting the Underlying Cause of PKU -

BEDFORD, Mass. December 16, 2019 – Homology Medicines, Inc. (Nasdaq: FIXX), a genetic medicines company, announced today a peer-reviewed publication of findings from a five-year retrospective chart review that demonstrated phenylalanine (Phe) concentrations remain elevated in adult patients with classical phenylketonuria (PKU) even when closely monitored and on the standard of care highly restricted protein diet. Elevated Phe can cause neurocognitive deficits and, as diet alone is often insufficient for achieving target Phe levels, these data support the need for new therapies to control Phe levels in patients with PKU. The publication describes a retrospective review of electronic health records of patients 10-40 years old with hyperphenylalaninemia (HPA), or mild, moderate or classical PKU, to capture historical data associated with managing PKU under the standard of care for the study’s time period of November 2012 through November 2017, characterize a representative population, and understand the unmet medical need.

“This retrospective analysis emphasizes the importance of developing new treatment options, including genetic medicines that aim to control Phe levels by addressing the genetic cause of PKU, obviating the need for a highly restrictive, difficult-to-maintain and often ineffective diet in the most common form of the disease, classical PKU,” said Albert Seymour, Ph.D., Chief Scientific Officer of Homology Medicines. “This work, conducted in collaboration with our academic partners, informed the design of our pheNIX gene therapy trial, from which we plan to share initial data this month.” The data were collected and analyzed at two specialized clinics — Boston Children’s Hospital in Boston, Massachusetts and the UPMC Children’s Hospital of Pittsburgh in Pittsburgh, Pennsylvania — in collaboration with Homology. The data were consistent between the two centers. Additional key observations in the publication include:

  • Of the 152 patients in the study, 65.8% had classical PKU, which is the most common and most severe form of the disease.
  • Although over 95% of patients were prescribed a Phe-restricted diet, blood Phe concentrations in the classical PKU patients remained substantially elevated above 360 µmol/L, a level considered well-controlled based on current U.S. treatment guidelines, particularly in patients with classical PKU.
  • As Phe threshold was lowered (Phe less than 600, 360, 120 or 30 µmol/L), the number of patients with consecutive lab values below the threshold decreased, suggesting many patients’ Phe levels were inadequately controlled.
  • 62.5% of patients were reported as having a history of at least one neuropsychiatric comorbidity, and adults were more likely than adolescents (69.5% vs. 54.3%).

The publication, “5-Year Retrospective Analysis of Patients with Phenylketonuria (PKU) and Hyperphenylalaninemia Treated at Two Specialized Clinics,” was peer-reviewed and published in the journal Molecular Genetics & Metabolism. For more information, please visit

About Homology Medicines, Inc.
Homology Medicines, Inc. is a genetic medicines company dedicated to transforming the lives of patients suffering from rare genetic diseases with significant unmet medical needs by curing the underlying cause of the disease. Homology’s proprietary platform is designed to utilize its human hematopoietic stem cell-derived adeno-associated virus vectors (AAVHSCs) to precisely and efficiently deliver genetic medicines in vivo either through a gene therapy or nuclease-free gene editing modality across a broad range of genetic disorders. Homology has a management team with a successful track record of discovering, developing and commercializing therapeutics with a particular focus on rare diseases, and intellectual property covering its suite of 15 AAVHSCs. Homology believes that its compelling preclinical data, scientific expertise, product development strategy, manufacturing capabilities and intellectual property position it as a leader in the development of genetic medicines. For more information, please visit

Forward-Looking Statements
This press release contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. All statements contained in this press release that do not relate to matters of historical fact should be considered forward-looking statements, including without limitation statements regarding our expectations surrounding the potential, safety, efficacy, and regulatory and clinical progress of our product candidates; beliefs about preclinical data and the properties and potential of our AAVHSCs; and our position as a leader in the development of genetic medicines. These statements are neither promises nor guarantees, but involve known and unknown risks, uncertainties and other important factors that may cause our actual results, performance or achievements to be materially different from any future results, performance or achievements expressed or implied by the forward-looking statements, including, but not limited to, the following: we have and expect to continue to incur significant losses; our need for additional funding, which may not be available; failure to identify additional product candidates and develop or commercialize marketable products; the early stage of our development efforts; potential unforeseen events during clinical trials could cause delays or other adverse consequences; risks relating to the capabilities and potential expansion of our manufacturing facility; risks relating to the regulatory approval process; our product candidates may cause serious adverse side effects; inability to maintain our collaborations, or the failure of these collaborations; our reliance on third parties; failure to obtain U.S. or international marketing approval; ongoing regulatory obligations; effects of significant competition; unfavorable pricing regulations, third-party reimbursement practices or healthcare reform initiatives; product liability lawsuits; failure to attract, retain and motivate qualified personnel; the possibility of system failures or security breaches; risks relating to intellectual property and significant costs as a result of operating as a public company. These and other important factors discussed under the caption “Risk Factors” in our Quarterly Report on Form 10-Q for the quarter ended September 30, 2019 and our other filings with the SEC could cause actual results to differ materially from those indicated by the forward-looking statements made in this press release. Any such forward-looking statements represent management’s estimates as of the date of this press release. While we may elect to update such forward-looking statements at some point in the future, we disclaim any obligation to do so, even if subsequent events cause our views to change.

Company Contacts:
Theresa McNeely SVP, Corporate Communications and Patient Advocate

Media Contact:
Cara Mayfield Senior Director, Patient Advocacy and Corporate Communications