at Oakland, California and other locations
study started
completion around
Principal Investigator
by Paul Harmatz
Headshot of Paul Harmatz
Paul Harmatz



A Global Phase III multicenter, randomized, assessor-blinded, active-controlled designed to evaluate safety and efficacy of study drug for the treatment of the MPS II.


Mucopolysaccharidosis II, Mucopolysaccharidoses, Idursulfase, JR-141 or Idursulfase, JR-141 2.0 mg/kg/week


You can join if…

  • A patient who voluntarily signs an Institutional Review Board or Independent Ethics Committee-approved written informed consent form. If the patient is aged under 18 years (aged under 16 years in the UK) at the time of enrollment or willingness to participate in the study cannot be confirmed due to MPS II-related intellectual disability, the patient's legally acceptable representative (e.g., his/her parents or guardians) may sign the informed consent on behalf of the patient. Written informed assent should be obtained from the patient, wherever possible.
  • Patients with confirmed diagnosis of MPS II
  • Naïve patients or patients who are receiving stable enzyme replacement therapy with idursulfase for more than 12 weeks before starting administration of JR-141 or idursulfase for this study.
  • Patients or patients whose partners are of child-bearing potential agree to use a medically accepted, highly effective method of contraception being use of condoms from the time of informed consent.

    <Cohort A>

  • Patients aged 36-42 months old at the time of ICF signing: patients must have a standard score measured by the BSID-III of 85 or less at screening.
  • Patients aged 43-71 months old at the time of ICF signing: patients must EITHER have (1) A DQ measured by BSID-III of 20 to 85 at screening OR (2) A composite standard score on NVI measured by KABC-II of 85 or less at screening (only who can perform KABC-II)
  • Patients aged 30-35 months old at the time of randomization and who are judged as having the severe phenotype by the Expert Board.

    <Cohort B>

  • Patients 6 years of age or older at the time of ICF signing and whose IQ are 70 and higher.
  • Enrollment of subjects in Cohort B is contingent on the availability in that country of a validated country-specific version of the test (either WISC-V, WAIS-IV, or T.O.V.A.).
  • Attenuated patients with 1 SD deficiency in the omission errors or variability domains of the T.O.V.A..

You CAN'T join if...

  • A patient with a history of HSCT with successful engraftment.
  • A patient who has received gene therapy treatment at any point.
  • Unable to undergo lumbar puncture.
  • A patient who is enrolled in another clinical study that involves clinical investigations or use of any investigational product (drug or device) within 4 months before obtaining informed consent.
  • Unable to comply with the protocol as determined by the principal investigator or subinvestigator.
  • Judged by the principal investigator or subinvestigator to be ineligible to participate in the study due to a history of serious drug allergy or sensitivity including anesthesia or hypersensitivity to any component of JR-141.
  • A patient who has a known or suspected local or general infection or is at risk of abnormal bleeding due to medical conditions or therapies.
  • A patient who has documented mutation of other genes, including loci adjacent to the IDS gene that are known to be associated with developmental delay, seizures, or other significant CNS disorders.
  • A patient who has documented loss of activity of sulfatases other than IDS.
  • A patient who has had a ventriculoperitoneal shunt placed or any other brain surgery, or has a clinically significant ventriculoperitoneal shunt malfunction within 30 days of screening.
  • full time employee of the sponsor or research site personnel directly affiliated with this study or their immediate family members.
  • A patient who otherwise is judged by the principle investigator or sub-investigator to be ineligible to participate in the study.

    [Only in France]

  • Persons deprived of their liberty by a judicial or administrative decision, according to article L.1121-6 the Public Health Code (Code de la santé publique), adults who are the subject of a measure of legal protection or unable to express their consent according to article L. 1121-8 of the Code de la santé publique)


  • UCSF Benioff Children's Hospital Oakland accepting new patients
    Oakland California 94609 United States
  • University of Minnesota accepting new patients
    Minneapolis Minnesota 55455 United States

Lead Scientist at UCSF

  • Paul Harmatz
    Dr. Paul Harmatz is a gastroenterologist who specializes in mucopolysaccharidoses (MPS) and other lysosomal storage diseases (genetic disorders in which a lack of certain enzymes results in progressive damage to cells and organ systems). He leads a team of specialists who diagnose and care for patients with these rare diseases, offering therapies such as weekly enzyme infusion.


accepting new patients
Start Date
Completion Date
JCR Pharmaceuticals Co., Ltd.
Phase 3 research study
Study Type
Expecting 80 study participants
Last Updated