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Safety, Tolerability and Preliminary Efficacy of JR-446 in Patients with Mucopolysaccharidosis Type IIIB (MPS IIIB)

Verified siteInvestigationalNo placebo
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What is this trial about?

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

The study focuses on Mucopolysaccharidosis Type IIIB, a rare genetic condition that causes a buildup of complex sugars in the brain and other organs, leading to a gradual loss of skills and physical abilities. The investigational medicine being tested is called JR-446. It is a specially designed protein that combines an enzyme called alpha-n-acetyl glucosaminidase fused to a humanised monoclonal antibody against transferrin receptor and is given by intravenous infusion.

The purpose of the study is to determine whether the medicine can be given safely and is tolerated by people with the disease. Participants will receive the infusion at scheduled visits over several months, and during the study they will have regular health checks, blood and urine samples, and imaging scans such as MRI to look at the brain.

Throughout the trial, doctors will watch for any side effects, reactions at the infusion site, and changes in basic health measurements like heart rhythm. The overall plan is to follow each participant for about a year to collect information on safety and early signs that the treatment may affect disease‑related markers.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and Consent

    After agreeing to join the study, you will sign a consent form that explains the purpose of the trial and your rights as a participant.

    The study team will confirm that you meet the eligibility criteria for mucopolysaccharidosis type IIIB.

  2. Step 2

    Baseline Assessments

    Before receiving any medication, you will undergo a series of baseline examinations.

    These include a physical examination, vital‑sign measurements, an electrocardiogram (ECG), and magnetic resonance imaging of the brain (MRI).

    Blood and urine samples will be collected to measure biomarkers such as heparan sulfate (HS) and neurofilament light chain (NfL).

    A sample of cerebrospinal fluid (CSF) may be taken to assess additional biomarkers.

    You will also complete questionnaires that evaluate neurological function and developmental progress.

  3. Step 3

    First Administration of JR-446

    You will receive the study drug JR-446 as an intravenous infusion.

    The medication is supplied as a powder that is mixed with a sterile solution immediately before infusion.

    The exact dose and infusion duration are determined by the study protocol and will be administered by qualified staff.

    During the infusion, your vital signs and any signs of infusion‑associated reactions will be closely monitored.

  4. Step 4

    Scheduled Follow‑Up Infusions

    You will return to the clinic for additional infusions of JR-446 at each scheduled visit.

    At every visit, the same monitoring procedures used during the first infusion will be repeated to ensure safety.

    The interval between infusions is defined by the study schedule; each infusion follows the same preparation and administration process.

  5. Step 5

    Periodic Safety and Efficacy Evaluations

    Throughout the trial, you will undergo regular assessments to evaluate safety and potential benefit.

    These assessments include blood and urine tests, repeat CSF sampling, vital‑sign checks, and ECG recordings.

    Brain MRI scans will be performed at designated time points to observe any changes in brain structure.

    Growth measurements (height, weight, body‑mass index) will be recorded using World Health Organization standards.

    Questionnaires and developmental scales will be administered to track changes in cognitive and functional abilities.

  6. Step 6

    Week 53 Final Evaluation

    At approximately week 53, you will complete the final study visit.

    All previously performed tests—including MRI, CSF biomarkers, blood and urine analyses, ECG, and growth measurements—will be repeated.

    The final questionnaires will capture any changes in neurological and developmental status since the start of the trial.

    The study team will compile the data to determine the safety, tolerability, and preliminary efficacy of JR-446.

Who can join the trial?

6 criteria

  • You must be younger than 6 years old when you (or your parent/guardian) give consent to join the study.
  • You need to be able to finish a cognitive test and score at least 55 on the standard scoring system. The test can be either the BSID-4 (a developmental assessment for young children) or the KABC-II (a test that measures thinking abilities in children).
  • You must have a confirmed laboratory diagnosis of MPS IIIB, meaning a medical test has officially identified the condition.
  • Your form of MPS IIIB should not be the slowly progressing (mild) type; it should be a more typical or faster‑progressing phenotype of the disease.
  • Both boys and girls are eligible to participate.
  • Because the study involves children, participants are considered a vulnerable group and receive special protections.

Who cannot join the trial?

9 criteria

  • Cannot have the procedure called a lumbar puncture (a needle placed in the lower back to collect fluid) or have heart or lung problems that would make sedation or anesthesia unsafe.
  • Cannot undergo an MRI scan (a type of imaging test that uses magnetic fields) if it is not possible for any reason.
  • Cannot have important lab test abnormalities, such as problems with the liver, kidneys, blood counts, or clotting ability, as judged by the doctor.
  • Cannot have taken any other experimental medicines (for example, enzyme replacement therapy, genistein, anakinra, ambroxol, or miglustat) within the last four months (or longer, depending on how long the drug stays in the body).
  • Cannot have received gene therapy or a stem cell transplant (called hematopoietic stem cell transplantation) that has successfully taken hold.
  • Cannot have a serious allergy or severe reaction to any part of the study drug JR‑446 or to other medicines that might be given during the trial.
  • Cannot have a history of bleeding problems or be taking medicines that could cause dangerous bleeding after a lumbar puncture, according to the doctor.
  • Cannot have frequent epileptic seizures that are not well controlled with seizure medication.
  • Cannot have blood test results that show infection with HIV, active hepatitis B, or active hepatitis C.
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Investigated drugs

JR-446 is an experimental treatment designed to replace a missing enzyme in people with Mucopolysaccharidosis Type IIIB (MPS IIIB). It combines the enzyme alpha‑N‑acetyl glucosaminidase with a specially engineered antibody that helps the enzyme enter cells by attaching to a protein called the transferrin receptor. In the trial the medicine is given as a powder that is mixed with liquid and delivered through an intravenous (IV) infusion. The study is testing whether JR‑446 is safe, can be tolerated, and shows any early signs of helping patients with this rare disease.

What is already known about the treatment

JR-446 - JR-446 is administered by intravenous infusion using a powder that is reconstituted into a solution for injection. It is an experimental orphan drug currently in Phase I/II clinical trials and has not yet received market approval. The medication is being studied to treat Mucopolysaccharidosis type IIIB, a rare inherited disorder that causes harmful sugar buildup in cells. It works by linking the enzyme alpha‑N‑acetyl glucosaminidase to a humanised antibody that binds the transferrin receptor, allowing the enzyme to enter cells and break down the stored sugars; it belongs to the class of targeted enzyme‑replacement therapies.

Investigated diseases

Mucopolysaccharidosis IIIB - A rare inherited lysosomal storage disorder caused by a deficiency of the enzyme N‑acetyl‑alpha‑D‑glucosaminidase, leading to buildup of heparan sulfate in cells. Symptoms typically appear in early childhood and include developmental delay, behavioral changes, and loss of previously acquired skills. As the disease advances, children experience progressive cognitive decline, speech and motor deterioration, and may develop seizures. Physical findings can include skeletal abnormalities, enlarged liver or spleen, and problems with vision or hearing. The condition worsens over time, with increasing neurodegeneration and functional impairment.
Trial detailsLast updated 13 Nov 2026
Age0-17PhasePhase ITrial ID2026-525372-26-00Protocol codeJR-446-201Estimated enrolment12 patientsSponsorJcr Pharmaceuticals Co. Ltd.

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