Mucopolysaccharidosis IIPhase 3NCT05594992
An Extension Study of JR-141 to Evaluate the Long-term Safety and Efficacy in MPS II (Hunter Syndrome) Subjects
A Phase 3 study testing JR-141 in people with Mucopolysaccharidosis II, run by JCR Pharmaceuticals Co., Ltd. at 10 sites in 8 countries.
Trial summary
An extension of Global Phase III open-label, multicenter designed to evaluate the Long-term safety and efficacy of study drug for the treatment of the MPS II. Read more about this study
- Who is it for?
- Any age
- Conditions the study is for
- Mucopolysaccharidosis II
- What is being tested?
- JR-141
- Type of treatment
- Injection or infusion
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 80 participants
- Where
- 10 sitesin 8 countries
- Study dates
- 22 Feb 2023to 28 Feb 2028
- Phase
- Phase 3
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages Any age
- All sexes
- No healthy volunteers
- Child, Adult, Older adult
Who may be able to join
- A subject who participated in the Parent Study (JR-141-GS31) and completed the assessments at Week 105 in Cohort A or Week 53 in Cohort B before being administered the study medication of that respective visit, and in the opinion of the principal investigator there are no safety concerns.
- A subject from whom an IRB or IEC-approved written informed consent can be obtained, which is voluntarily signed. If the subject 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 subject's legally acceptable representative (e.g., his parents or guardians) may sign the ICF on behalf of the subject. Written informed assent should be obtained from the subject, wherever possible.
- Female subject of child bearing potential or male subject whose female partner is of child-bearing potential, i.e., fertile, following menarche and until becoming post-menopausal unless permanently sterile, agrees to use a medically accepted, highly effective method of contraception from the time of signing the ICF. The method of contraception must be used during the study until 90 days for male subjects, and 30 days for female subjects after the final study drug administration.
Who cannot join
- A subject who changed treatment from JR-141 to idursulfase during the treatment period in the Parent Study (JR-141-GS31).
- A subject who is unable to comply with the protocol (e.g., is unable to return for safety evaluations or is otherwise unlikely to complete the study) as determined by the principal investigator or sub-investigator.
- [Only in France] Persons deprived of their liberty by a judicial or administrative decision, according to article L. 1121-6 of the Public Health Code (Code de la santé publique, CSP) 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 CSP.
Trial locations and contacts
10 sites in 8 countries. Contact the study team or a site near you to ask about taking part.
10 sites in 8 countries
United States2 sites
UCSF Benioff Children's Hospital Oakland
Oakland, California, 94609
Children's Hospital of Philadelphia
Philadelphia, Pennsylvania, 19104
Brazil2 sites
Hospital de Clínicas de Porto Alegre
Porto Alegre
Instituto de Genética e Erros Inatos do Metabolismo
São Paulo
About this study
Official title: An Extension Study of JR-141 to Evaluate the Long-term Safety and Efficacy in Mucopolysaccharidosis Type II (Hunter Syndrome) Subjects
An extension of Global Phase III open-label, multicenter designed to evaluate the Long-term safety and efficacy of study drug for the treatment of the MPS II.
- Conditions
- Mucopolysaccharidosis II
- Being tested
- JR-141
- Medical subject headings
- Mucopolysaccharidosis II
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
JR-141Drug
IV infusion, 2.0 mg/kg/week
| Study group | Role | What they receive |
|---|---|---|
| JR-141 2.0 mg/kg/week | Experimental | Not described Receives: Drug: JR-141 |
What is being measured
The primary outcome is the main question the study is designed to answer.
Change in heparan sulfate concentrations in cerebrospinal fluid from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study to each time point
Assessment will be mandatory for the first two years after starting JR-141 administration through the parent study or the extension study.
Measured: [A-1, A-2, A-3: Week 157, 209, 261] [A-4: Week 131, 183, 235, 287]
Change in neurocognitive testing, calculated by the BSID-III or KABC-II, from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Measured: [A-1: Week 157, 209, 261] [A-2: Week 131, 157, 183, 209, 261] [A-3: Week 131, 157, 209, 261 ] [A-4: Week 131, 157, 183, 235, 287]
Change in neurocognitive testing, calculated by the VABS-II from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Measured: [A-1: Week 157, 209, 261] [A-2: Week 131, 157, 183, 209, 261] [A-3: Week 131, 157, 209, 261 ] [A-4: Week 131, 157, 183, 235, 287][B-1: Week 78, 105, 157, 209, 261] [B-2: Week 78, 105, 131, 157, 209, 261]
Change in neurocognitive testing, calculated by the Wechsler, from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Measured: [B-1: Week 78, 105, 157, 209, 261] [B-2: Week 78, 105, 131, 157, 209, 261]
Secondary outcomes (2)
Change in liver and spleen volume from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Measured: [A-1, A-3: Week 157, 209, 261] [A-2: Week 131, 157, 209, 261] [A-4: Week 131, 183, 235, 287] [B-1: Week 105, 157, 209, 261] [B-2: Week 78, 105, 157, 209, 261]
Change in 6-minute walk distance from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Measured: [B-1: Week 105, 157, 209, 261] [B-2: Week 78, 105, 157, 209, 261]
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted26 Oct 2022
- Study start22 Feb 2023
- Primary completion28 Feb 2028 (estimated)
- Study completion28 Feb 2028 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Mucopolysaccharidosis IIStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 3
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Enrolment
- 80 participants (estimated)
Sponsor and investigators
- Lead sponsor
- JCR Pharmaceuticals Co., Ltd.
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT05594992
- Sponsor's protocol ID
- JR-141-GS32
- Status last verified
- Jan 2026
- First submitted
- 6 Oct 2022
- Last updated
- 21 Jan 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
Study at a glance
From the registry record, last updated by the sponsor on 21 Jan 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- An Extension Study of JR-141 to Evaluate the Long-term Safety and Efficacy in Mucopolysaccharidosis Type II (Hunter Syndrome) Subjects
- ClinicalTrials.gov ID
- NCT05594992
- Acronym / sponsor ID
- JR-141-GS32
- Conditions
- Mucopolysaccharidosis II
- Phase
- Phase 3
- Study type
- Interventional
- Recruitment status
- Enrolling by invitation
- Enrolment
- 80 participants (estimated)
- Lead sponsor
- JCR Pharmaceuticals Co., Ltd.Industry (pharma, biotech, devices)
- Study start
- 22 Feb 2023 (actual)
- Primary completion
- 28 Feb 2028 (estimated)
- Study completion
- 28 Feb 2028 (estimated)
- First posted
- 26 Oct 2022 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
An extension of Global Phase III open-label, multicenter designed to evaluate the Long-term safety and efficacy of study drug for the treatment of the MPS II.
Study design
- Primary purpose
- Treatment
- Allocation
- Not applicable
- Intervention model
- Single group
- Masking
- None (open label)
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| JR-141 2.0 mg/kg/week | Experimental | Drug: JR-141 |
Who may qualify
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Child, Adult, Older adult
Key inclusion criteria (3 listed)
- A subject who participated in the Parent Study (JR-141-GS31) and completed the assessments at Week 105 in Cohort A or Week 53 in Cohort B before being administered the study medication of that respective visit, and in the opinion of the principal investigator there are no safety concerns.
- A subject from whom an IRB or IEC-approved written informed consent can be obtained, which is voluntarily signed. If the subject 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 subject's legally acceptable representative (e.g., his parents or guardians) may sign the ICF on behalf of the subject. Written informed assent should be obtained from the subject, wherever possible.
- Female subject of child bearing potential or male subject whose female partner is of child-bearing potential, i.e., fertile, following menarche and until becoming post-menopausal unless permanently sterile, agrees to use a medically accepted, highly effective method of contraception from the time of signing the ICF. The method of contraception must be used during the study until 90 days for male subjects, and 30 days for female subjects after the final study drug administration.
Key exclusion criteria (3 listed)
- A subject who changed treatment from JR-141 to idursulfase during the treatment period in the Parent Study (JR-141-GS31).
- A subject who is unable to comply with the protocol (e.g., is unable to return for safety evaluations or is otherwise unlikely to complete the study) as determined by the principal investigator or sub-investigator.
- [Only in France] Persons deprived of their liberty by a judicial or administrative decision, according to article L. 1121-6 of the Public Health Code (Code de la santé publique, CSP) 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 CSP.
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| JR-141IV infusion, 2.0 mg/kg/week | Drug | JR-141 2.0 mg/kg/week |
Primary outcome
Change in heparan sulfate concentrations in cerebrospinal fluid from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study to each time point
Time frame: [A-1, A-2, A-3: Week 157, 209, 261] [A-4: Week 131, 183, 235, 287]
Assessment will be mandatory for the first two years after starting JR-141 administration through the parent study or the extension study.
Change in neurocognitive testing, calculated by the BSID-III or KABC-II, from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Time frame: [A-1: Week 157, 209, 261] [A-2: Week 131, 157, 183, 209, 261] [A-3: Week 131, 157, 209, 261 ] [A-4: Week 131, 157, 183, 235, 287]
Change in neurocognitive testing, calculated by the VABS-II from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Time frame: [A-1: Week 157, 209, 261] [A-2: Week 131, 157, 183, 209, 261] [A-3: Week 131, 157, 209, 261 ] [A-4: Week 131, 157, 183, 235, 287][B-1: Week 78, 105, 157, 209, 261] [B-2: Week 78, 105, 131, 157, 209, 261]
Change in neurocognitive testing, calculated by the Wechsler, from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Time frame: [B-1: Week 78, 105, 157, 209, 261] [B-2: Week 78, 105, 131, 157, 209, 261]
2 secondary outcomes
Change in liver and spleen volume from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Time frame: [A-1, A-3: Week 157, 209, 261] [A-2: Week 131, 157, 209, 261] [A-4: Week 131, 183, 235, 287] [B-1: Week 105, 157, 209, 261] [B-2: Week 78, 105, 157, 209, 261]
Change in 6-minute walk distance from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study
Time frame: [B-1: Week 105, 157, 209, 261] [B-2: Week 78, 105, 157, 209, 261]
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 21 Jan 2026.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
The record lists no contact. Use the official record to reach the sponsor.
10 sites in 8 countries: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 3 study testing JR-141 in people with Mucopolysaccharidosis II, run by JCR Pharmaceuticals Co., Ltd. at 10 sites in 8 countries.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 3 inclusion and 3 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: enrolling by invitation, as of the sponsor's last update on 21 Jan 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 10 sites in United States, Brazil, Argentina, France, Germany and 3 more countries. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
The record lists no contact. The official record names the sponsor, who can be asked directly. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Change in heparan sulfate concentrations in cerebrospinal fluid from each subject's first administration of JR-141 throughout the Parent Study (JR-141-GS31) or this study to each time point (time frame: [A-1, A-2, A-3: Week 157, 209, 261] [A-4: Week 131, 183, 235, 287]). The study lists 4 primary outcomes in all. It is what the study was designed to measure, not a finding.
Where can I read the original study information?
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 21 Jan 2026.