Hunter syndrome drug JR-141 tested for Long-Term safety
NCT ID NCT05594992
First seen Jun 24, 2026 · Last updated Jun 27, 2026 · Updated 1 time
Summary
This study is an extension of a previous trial testing JR-141, a drug given weekly by IV, for people with Hunter syndrome (a rare genetic disorder). It aims to see if the drug remains safe and effective over a longer period. About 80 participants who completed the earlier study will continue receiving JR-141, and researchers will track changes in spinal fluid markers, thinking skills, and physical abilities.
What this could mean
Our plain-language read of the trial. This is informational only, not medical advice or a prediction.
- Active substance
- JR-141 (a drug given by IV infusion weekly)
- What this could lead to
- If successful, this could confirm that JR-141 safely controls Hunter syndrome symptoms long-term, offering a continued treatment option for patients.
- What could go wrong
- This is an extension study, so it builds on earlier results but is still open-label (no placebo). Long-term benefits are not guaranteed, and side effects may emerge over time.
This is an AI summary of the original study and may miss details. Read our disclaimer.
Study facts
What this study's own registry entry says, in plain language.
- Phase
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Phase 3
Large-scale testing in a bigger group. Usually the last step before a treatment can be approved.
- Participants
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About 80 people
The number the study aims to enrol. It can still change while the study runs.
- Started
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Feb 2023
- Expected to finish
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Feb 2028
An estimate. End dates often move.
- Lead sponsor
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A company
The lead sponsor is a pharmaceutical, biotech, or medical-device company.
Who can take part
This study's own entry requirements. Only the study team can say for certain whether you qualify.
- Ages
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Children (under 18), adults (18 to 64) and older adults (65 and over)
- Sex
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Anyone
- Healthy volunteers
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Not accepted
This study is not open to healthy volunteers. The entry requirements below say who it is open to.
Show the full entry requirements Hide the full entry requirements
Copied word for word from the study's registry entry, so the wording is the study team's rather than ours.
Inclusion Criteria: 1. 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. 2. 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. 3. 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. Exclusion Criteria: 1. A subject who changed treatment from JR-141 to idursulfase during the treatment period in the Parent Study (JR-141-GS31). 2. 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. 3. \[Only in France\] 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.
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Conditions
The condition(s) this trial relates to.
As listed by the trial registrant
The condition terms exactly as the trial's registrant entered them.
How to take part
Only the study team decides who joins. These are the ways to reach them.
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The places running it
10 sites in 8 countries. The list below names each one and where it is.
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The official record
The full official record for this study. This one lists no contact details, but it is the first place any would appear.
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A doctor treating you
A doctor who knows your case can contact a study site on your behalf, and can tell you whether this study is worth pursuing at all.
Contacts and locations
Locations
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Children's Hospital of Philadelphia
Philadelphia, Pennsylvania, 19104, United States
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Hospital Sant Joan de Déu
Barcelona, Spain
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Hospital Universitario Austral
Buenos Aires, Argentina
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Hospital de Clínicas de Porto Alegre
Porto Alegre, Brazil
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Hôpital Femme Mère Enfant
Bron, France
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Instituto de Genética e Erros Inatos do Metabolismo
São Paulo, Brazil
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Osp. Pediatrico Bambino Gesù, IRCCS
Rome, Italy
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UCSF Benioff Children's Hospital Oakland
Oakland, California, 94609, United States
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Universitätsklinikum Hamburg-Eppendorf
Hamburg, Germany
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Uniwersytecki Szpital Dziecięcy
Krakow, Poland
More trials for these conditions
Other studies related to the condition(s) this trial covers.
- New enzyme therapy aims to reach the brain in MPS II
- Can a new enzyme therapy tame MPS II over time?
- Can a weekly infusion slow the toll of a rare genetic disease?
- Can a One-Time gene therapy change the future of MPS II?
- Gene Editing's lasting impact: a 10-Year safety watch
- New registry aims to unlock secrets of rare childhood diseases