A Phase 1/Phase 2 open-label study to evaluate the safety, tolerability, and efficacy of a single intravenous administration of an investigational medication in adult participants with phenylketonuria (PKU)-Tx Tester
Investigating Gene Therapy for Phenylketonuria (PKU)

Study Overview
This study is looking for individuals 18 to 65 years old with PKU. Sanofi believes that everyone
should have the opportunity to take part in clinical trials. It is important to include people who
have been historically under-represented in clinical trials. Sanofi is committed to inclusivity in
our studies.
If you are interested in learning more about this study, we encourage you to complete a brief
questionnaire to help determine if you may qualify to participate and be referred to a site
recruiting in your area for further evaluation.
PKU is an inherited disorder caused by abnormalities in the gene coding for the phenylalanine
hydroxylase (PAH) enzyme, which increases the levels of Phenylalanine (Phe), a building block
of proteins in the blood. If PKU is not adequately treated, Phe can increase to harmful levels in
the body, causing injury to the brain and the nerves in your body. The usual treatment for
participants with PKU is strict dietary protein restriction along with manufactured medical foods
that are low in protein and Phe. A daily medication injection is also available.
The purpose of the study is to evaluate the safety and efficacy of an investigational gene
therapy in reducing phenylalanine (Phe) levels and in the elimination of a Phe restricted diet.
Study Details
The investigational gene therapy will insert a copy of the gene into your liver to stimulate your
liver to produce an enzyme (a protein that breaks down Phe) to lower blood Phe levels. This
enzyme converts the Phe present in your blood into other essential proteins that keep the brain
and nerves in your body healthy.
• This is an open label study (everyone on the study will receive the investigational gene
therapy) which is injected once (into the arm).
• Approximately 32 individuals will participate in this study.
• The study will last approximately 102 weeks (about 2 years). This includes
approximately 6 weeks for the screening period, 1 day for the treatment period and
approximately 96 weeks for the follow-up period.
1. Screening period (6 weeks): Various tests will be done to determine if you are
eligible for the study.
2. Treatment: The injection will be administered, and you will stay overnight for
observation for a minimum duration of 24 hours for monitoring.
3. Follow-up (96 weeks): Approximately 41 study visits, up to two times per week.
Some visits are at the study site and some visits can be performed as remote visits,
where study assessments can be done by a qualified in-home service provider at
your home.
Eligibility Criteria
Inclusion Criteria:
Exclusion Criteria:
This study investigates the use of an investigational gene therapy for individuals with phenylketonuria (PKU). PKU is a genetic disorder that affects the body's ability to break down phenylalanine (Phe), a component of proteins. If not managed properly, high levels of Phe can harm the brain and nerves. Current treatments include a strict low-protein diet and special medical foods, along with daily medication injections. The purpose of this study is to evaluate whether the investigational gene therapy can reduce Phe levels and eliminate the need for a Phe-restricted diet.
The study involves receiving a single injection of the investigational gene therapy, which is designed to insert a copy of a gene into the liver. This gene helps the liver produce an enzyme that breaks down Phe, converting it into other proteins necessary for maintaining healthy brain and nerve function. Participants will undergo a screening period with various tests, followed by the treatment, and then a follow-up period involving approximately 41 visits over 96 weeks. Some visits may be conducted remotely by a qualified service provider.
- Who can participate: Individuals aged 18 to 65 years with PKU are eligible to participate. Key eligibility factors include a diagnosis of PKU and the ability to comply with study procedures.
- Study details: Participants will receive a single injection of the investigational gene therapy. The study includes a screening period, treatment, and follow-up visits. A placebo is not used in this study.
- Study Timelines and Visits: The study will last 102 weeks. The study requires 41 visits.