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Study on the Effectiveness and Safety of SYNB1934 for Adults with Phenylketonuria (PKU)

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What is this trial about?

A plain-language summary of the goals, design and what participants do

This clinical trial is focused on studying a condition called Phenylketonuria (PKU), a rare genetic disorder that affects how the body processes a substance called phenylalanine, which is found in many foods. The study is testing a new treatment known as SYNB1934v1, which is a specially modified strain of bacteria called Escherichia coli. This bacteria is designed to help reduce the levels of phenylalanine in the blood. The treatment is given in the form of a powder that is mixed with water and taken by mouth.

The purpose of the study is to evaluate the effectiveness and safety of SYNB1934v1 in people with PKU. The study is divided into different parts. Initially, participants will receive increasing doses of the treatment to find the most effective dose. After this, there will be a period where participants will be randomly assigned to continue with the treatment or switch to a placebo. This helps researchers understand how well the treatment works compared to no treatment. Finally, there will be an open-label period where all participants will receive the treatment to further assess its safety and tolerability.

In addition to SYNB1934v1, some participants may also receive other medications like Ondansetron, which is used to prevent nausea, and Esomeprazole, a medication that reduces stomach acid. These medications are given to manage any side effects that might occur during the study. The study will last for several weeks, and participants will be monitored closely to ensure their safety and to gather information on how the treatment affects their phenylalanine levels.

The research process

The trial runs in 3 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Dose escalating, open-label period (part 1)

    During this period, you will begin taking the study medication called SYNB1934v1. This medication is taken orally as a powder mixed with liquid. The dose will be gradually increased to find the most effective amount for you.

    Your blood levels of phenylalanine, a substance that people with phenylketonuria (PKU) have difficulty processing, will be monitored regularly. The goal is to see a change in these levels.

    You will also be asked to continue your current diet and any other treatments you are using, such as sapropterin or sepiapterin, without changes.

  2. Step 2

    Randomized withdrawal period (part 2)

    In this phase, you will be randomly assigned to continue taking SYNB1934v1 or a placebo, which looks like the medication but does not contain the active ingredient. This is to compare the effects of the medication against no treatment.

    Your blood phenylalanine levels will continue to be monitored to evaluate the effectiveness of the medication.

    This period lasts for four weeks, and you will need to maintain your current diet and treatments.

  3. Step 3

    Open-label extension (part 3)

    In this final phase, all participants will receive SYNB1934v1 to assess its long-term safety and tolerability.

    Regular monitoring of your blood phenylalanine levels will continue, along with checks on your overall health and any side effects you may experience.

    You will be asked to continue your current diet and treatments throughout this period.

Who can join the trial?

8 criteria

  • Must be at least 18 years old. Participants aged 12 to 17 may join after the first 20 adults have completed the initial part of the study, with special approval.
  • Must be able and willing to complete the consent process. This means adults or their parents/guardians must agree to participate, and minors must also agree.
  • Must have a diagnosis of Phenylketonuria (PKU) and have difficulty maintaining recommended blood levels of phenylalanine (Phe) despite current treatments. This is shown by having uncontrolled blood Phe levels greater than 360 micromoles per liter (µmol/L) during screening and in recent medical history.
  • Females who can have children must have a negative pregnancy test at the start and end of certain study parts and be willing to take additional pregnancy tests during the study.
  • Sexually active females who can have children must agree to use a highly effective method of birth control while in the study and for 2 weeks after the last dose of the study medication.
  • Must have a stable diet, including any special medical formula, for at least 1 month before screening.
  • If using medications like sapropterin or sepiapterin, must be on a stable dose for at least 3 months before the study.
  • Must be willing and able to continue their current diet and any medications like sapropterin, sepiapterin, and large neutral amino acids without changes during the study and participate in all study activities.

Who cannot join the trial?

8 criteria

  • Patients who do not have the condition called Phenylketonuria cannot participate.
  • Patients who are not within the age range specified for the study cannot participate. The study includes children and adults.
  • Patients who are not willing to follow the study procedures and requirements cannot participate.
  • Patients who have other medical conditions that might interfere with the study cannot participate.
  • Patients who are pregnant or breastfeeding cannot participate.
  • Patients who are currently participating in another clinical trial cannot participate.
  • Patients who have a history of allergic reactions to the study medication cannot participate.
  • Patients who have used certain medications recently that might affect the study results cannot participate.
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Investigated drugs

SYNB1934 is a medication being studied for its potential to help people with a condition called phenylketonuria, or PKU. PKU is a genetic disorder where the body cannot break down an amino acid called phenylalanine, which can lead to health problems if it builds up in the blood. This medication is designed to help reduce the levels of phenylalanine in the blood, which may help manage the symptoms of PKU. The study aims to see how well this medication works and how safe it is for patients to use over time.

What is already known about the treatment

SYNB1934 – SYNB1934 is an investigational medication administered orally, designed to help manage phenylketonuria (PKU), a genetic disorder that affects the body's ability to break down the amino acid phenylalanine. Currently, SYNB1934 is being studied in clinical trials to determine its effectiveness and safety. The main therapeutic goal is to reduce blood phenylalanine levels in patients with PKU. At the molecular level, SYNB1934 works by using engineered bacteria to consume phenylalanine in the gut, thereby lowering its levels in the bloodstream. It is classified as a therapeutic agent for metabolic disorders.

Investigated diseases

Phenylketonuria – Phenylketonuria is a genetic disorder characterized by the body's inability to break down an amino acid called phenylalanine. This condition is caused by a deficiency in the enzyme phenylalanine hydroxylase, which is necessary for converting phenylalanine into another amino acid, tyrosine. As a result, phenylalanine accumulates in the blood and can lead to various health issues. If untreated, high levels of phenylalanine can affect brain development and function. The progression of the disease can lead to intellectual disabilities, behavioral problems, and seizures. Early detection and management are crucial to prevent these complications.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2022-502932-37-00Protocol codeSYNB1934-CP-003Estimated enrolment150 patientsSponsorSynlogic Inc.

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