Homology Medicines has discontinued the development of this program.

This is a Phase 1/2, open-label, randomized, concurrently-controlled, dose escalation study to evaluate the safety and efficacy of HMI-102 in adult PKU subjects with PAH deficiency. Participants will receive a single administration of HMI-102 and will be followed for safety and efficacy for 1 year.

Part 1 of this study will evaluate the safety and efficacy of HMI-102 gene therapy in adult subjects with PKU due to PAH deficiency. Subjects will receive a single dose of HMI-102 administered intravenously. Up to 3 dose levels of HMI-102 may be investigated in this study. At a given dose level, a minimum of 2 subjects will be enrolled and dosed. Dosing of the first two subjects will be staggered. Following evaluation of data from the first 2 subjects in a cohort, a decision can be made to either escalate to the next dose level or expand the cohort at the selected dose level. Additional doses may be added by HMI to investigate intermediate or higher doses.

In Part 2 dose expansion, evaluation of up to 2 dose levels is planned. Subjects will be randomized to receive HMI-102 or a concurrent delayed treatment control arm. Subjects in the delayed treatment control will be eligible to receive HMI-102 after 28 weeks.

Key Inclusion Criteria:

• Adults 18-55 years of age at the time of informed consent
• Diagnosis of phenylketonuria (PKU) due to PAH deficiency
• Two plasma Phe values with a concentration of ≥ 600 μmol/L drawn at least 72 hours apart during the screening period and at least one historical value ≥ 600 μmol/L in the preceding 24 months.
• Subject has the ability and willingness to maintain their baseline diet, whether Phe-restricted or unrestricted for the duration of the trial, unless otherwise directed

Key Exclusion Criteria:

• Subjects with PKU that is not due to PAH deficiency
• Presence of anti-AAVHSC15 neutralizing antibodies
• ALT > ULN and AST > ULN
• Alkaline phosphatase > ULN.
• Total bilirubin > ULN, direct bilirubin > ULN
• Serum creatinine >1.5x ULN
• International normalized ratio (INR) > 1.2
• Hematology values outside of the normal range (hemoglobin <11.0 g/dL for males or <10.0 g/dL for females; white blood cells (WBC) <3,000/μL; absolute neutrophils <1500/μL; platelets <100,000/μL)
• Hemoglobin A1c >6.5% or fasting glucose >126 mg/dL
• Any clinically significant abnormal laboratory result at screening, in the opinion of the Investigator
• Contraindication to corticosteroid use or conditions that could worsen in the presence of corticosteroids, as assessed and determined by the investigator
• Previously received gene therapy for the treatment of any condition.