Mucopolysaccharidosis IINCT04597385
Long-term Follow-Up for RGX-121
An observational study of Mucopolysaccharidosis II, run by REGENXBIO Inc. at 4 sites in 2 countries.
Trial summary
RGX-121-5101 is an observational long-term follow-up study to the RGX-121-101 or RGX-121-1102 studies where participants received RGX-121, a gene therapy intended to deliver a functional copy of the iduronate-2-sulfatase gene (IDS) to the central nervous system. Read more about this study
- Who is it for?
- Any age, men only
- Conditions the study is for
- Mucopolysaccharidosis II
- What is being tested?
- Long-term Follow-Up
- How many people
- 27 participants
- Where
- 4 sitesin 2 countries
- Study dates
- 14 Mar 2021to Oct 2028
- Phase
- Observational
- 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
- Men only
- No healthy volunteers
- Child, Adult, Older adult
Study population: Up to 54 subjects who have received RGX-121 in a previous parent study.
Who may be able to join
- To be eligible, a participant must have previously received RGX-121 in a separate parent trial.
- Participant or participant's legal guardian(s) is/(are) willing and able to provide written, signed informed consent
Who cannot join
- Participant has not received RGX-121 previously in a separate parent trial.
Trial locations and contacts
4 sites in 2 countries.
4 sites in 2 countries
United States3 sites
Saint Peter's Healthcare System
New Brunswich, New Jersey, 08901
The Children's Hospital of Philadelphia (CHOP)
Philadelphia, Pennsylvania, 19104
University of California, San Francisco (UCSF)- Benioff Children's Hospital
San Francisco, California, 94158
About this study
Official title: A Long-term Follow-up Study to Evaluate the Safety and Efficacy of RGX-121
RGX-121-5101 is an observational long-term follow-up study to the RGX-121-101 or RGX-121-1102 studies where participants received RGX-121, a gene therapy intended to deliver a functional copy of the iduronate-2-sulfatase gene (IDS) to the central nervous system. This study will evaluate the long-term safety and efficacy of RGX-121.
Read the detailed description
This is a prospective follow-up study to evaluate the long-term safety and efficacy after a single administration of RGX-121. Eligible participants are those who previously have enrolled in clinical study RGX-121-101 or RGX-121-1102 and received a single intracisternal (IC) or intracerebroventricular (ICV) infusion of RGX-121. Enrollment of each participant will occur the same day or after the participant has completed the end of study (EOS) visit or early termination visit (ET) from the previous (parent) study. Participants will be followed in this study cumulatively for up to 5 years after RGX-121 administration (inclusive of the parent study). No treatment will be administered under this observational protocol. The total study duration for each participant may vary depending on when they enroll in the current study following RGX-121 administration in the parent study.
- Conditions
- Mucopolysaccharidosis II
- Being tested
- Long-term Follow-Up
- Keywords
- MPS II, Gene Therapy, Hunter
- Medical subject headings
- Mucopolysaccharidosis II, Sudden Infant Death
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
Long-term Follow-UpOther
No intervention
| Study group | Role | What they receive |
|---|---|---|
| Long-term Follow-Up | No intervention. Receives: Other: Long-term Follow-Up |
What is being measured
The primary outcome is the main question the study is designed to answer.
Long-term Safety of RGX-121
To evaluate the safety of RGX-121 serious and adverse events as assessed by Common Terminology Criteria for Adverse Events (CTCAE Version 5.0).
Measured: 5 years inclusive of parent study
Secondary outcomes (8)
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Bayley Scales of Infant and Toddler Development, 3rd Edition)
To evaluate the long-term effect of RGX-121 on neurodevelopmental parameters as measured by the BSID-III. The BSID-III assesses children aged 1 to 42 months across several domains (cognitive, language, and motor domains) to give a holistic view of the participants' development and potential delays.
Measured: 5 years inclusive of parent study
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Kaufman Assessment Battery for Children, 2nd Edition)
To evaluate the long-term effect of RGX-121 on neurodevelopmental parameters as measured by the KABC-II. The KABC-II is an individually administered measure of the cognitive processing abilities of children and adolescents aged 3 through 18.
Measured: 5 years inclusive of parent study
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Mullen Scales of Early Learning)
To evaluate the long-term effect of RGX-121 on neurodevelopmental parameters as measured by the MSEL. The MSEL is a standardized developmentally integrated system that assesses language, motor, and perceptual abilities, and measures cognitive ability and motor development.
Measured: 5 years inclusive of parent study
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Vineland Adaptive Behavior Scales, 2nd Edition)
To evaluate the long-term effects of RGX-121 on neurodevelopmental parameters as measured by the VABS-II. The VABS-II assesses adaptive behavior in individuals from infancy to age 90 years. The VABS-II offers a way to measure personal and social self-sufficiency in real-life situations and to observe how these cognitive abilities impact the autonomy management process when put into practice
Measured: 5 years inclusive of parent study
Evaluate the long-term impact of RGX-121 on Plasma Biomarkers (I2S)
To evaluate the long-term impact of RGX-121 on Plasma biomarker Iduronate-2-sulfatase (I2S) through plasma collection for participants not receiving ERT (discontinued or naïve).
Measured: 5 years inclusive of parent study
Evaluate the long-term impact of RGX-121 on CSF Biomarkers (I2S)
To evaluate the long-term impact of RGX-121 on CSF Biomarker Iduronate-2-sulfatase (I2S) through lumbar puncture.
Measured: 5 years inclusive of parent study
Evaluate the long-term impact of RGX-121 on CSF Biomarkers (GAGs)
To evaluate long-term impact of RGX-121 on CSF Biomarker Glycosaminoglycans (GAGs) through lumbar puncture.
Measured: 5 years inclusive of parent study
Long-term effect of RGX-121 on Urine Biomarker (GAGs)
To evaluate the long-term impact of RGX-121 on Urine Biomarker Glycosaminoglycans (GAGs) through urine analysis.
Measured: 5 years inclusive of parent study
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted22 Oct 2020
- Study start14 Mar 2021
- Primary completionOct 2028 (estimated)
- Study completionOct 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
- Observational
- Observational model
- Other
- Time perspective
- Prospective
- Enrolment
- 27 participants (actual)
Sponsor and investigators
- Lead sponsor
- REGENXBIO Inc.
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT04597385
- Sponsor's protocol ID
- RGX-121-5101
- Status last verified
- Aug 2026
- First submitted
- 15 Oct 2020
- Last updated
- 19 Aug 2026
- Results posted
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
Study at a glance
From the registry record, last updated by the sponsor on 19 Aug 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A Long-term Follow-up Study to Evaluate the Safety and Efficacy of RGX-121
- ClinicalTrials.gov ID
- NCT04597385
- Acronym / sponsor ID
- RGX-121-5101
- Conditions
- Mucopolysaccharidosis II
- Keywords
- MPS II, Gene Therapy, Hunter
- Study type
- Observational
- Recruitment status
- Active, not recruiting
- Enrolment
- 27 participants (actual)
- Lead sponsor
- REGENXBIO Inc.Industry (pharma, biotech, devices)
- Study start
- 14 Mar 2021 (actual)
- Primary completion
- Oct 2028 (estimated)
- Study completion
- Oct 2028 (estimated)
- First posted
- 22 Oct 2020 (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.
RGX-121-5101 is an observational long-term follow-up study to the RGX-121-101 or RGX-121-1102 studies where participants received RGX-121, a gene therapy intended to deliver a functional copy of the iduronate-2-sulfatase gene (IDS) to the central nervous system. This study will evaluate the long-term safety and efficacy of RGX-121.
Detailed description
This is a prospective follow-up study to evaluate the long-term safety and efficacy after a single administration of RGX-121. Eligible participants are those who previously have enrolled in clinical study RGX-121-101 or RGX-121-1102 and received a single intracisternal (IC) or intracerebroventricular (ICV) infusion of RGX-121. Enrollment of each participant will occur the same day or after the participant has completed the end of study (EOS) visit or early termination visit (ET) from the previous (parent) study. Participants will be followed in this study cumulatively for up to 5 years after RGX-121 administration (inclusive of the parent study). No treatment will be administered under this observational protocol. The total study duration for each participant may vary depending on when they enroll in the current study following RGX-121 administration in the parent study.
Study design
- Observational model
- Other
- Time perspective
- Prospective
- Number of arms
- 1
| Arm | Type | Receives |
|---|---|---|
| Long-term Follow-Up | – | Other: Long-term Follow-UpNo intervention. |
Who may qualify
- Sex
- Male only
- Healthy volunteers
- Not accepted
- Age groups
- Child, Adult, Older adult
- Study population
- Up to 54 subjects who have received RGX-121 in a previous parent study.
Key inclusion criteria (2 listed)
- To be eligible, a participant must have previously received RGX-121 in a separate parent trial.
- Participant or participant's legal guardian(s) is/(are) willing and able to provide written, signed informed consent
Key exclusion criteria (1 listed)
- Participant has not received RGX-121 previously in a separate parent trial.
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 |
|---|---|---|
| Long-term Follow-UpNo intervention | Other | Long-term Follow-Up |
Primary outcome
Long-term Safety of RGX-121
Time frame: 5 years inclusive of parent study
To evaluate the safety of RGX-121 serious and adverse events as assessed by Common Terminology Criteria for Adverse Events (CTCAE Version 5.0).
8 secondary outcomes
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Bayley Scales of Infant and Toddler Development, 3rd Edition)
Time frame: 5 years inclusive of parent study
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Kaufman Assessment Battery for Children, 2nd Edition)
Time frame: 5 years inclusive of parent study
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Mullen Scales of Early Learning)
Time frame: 5 years inclusive of parent study
Evaluate the long-term effect of RGX-121 on neurodevelopmental parameters of cognitive, motor, behavioral, and adaptive function (Vineland Adaptive Behavior Scales, 2nd Edition)
Time frame: 5 years inclusive of parent study
Evaluate the long-term impact of RGX-121 on Plasma Biomarkers (I2S)
Time frame: 5 years inclusive of parent study
Evaluate the long-term impact of RGX-121 on CSF Biomarkers (I2S)
Time frame: 5 years inclusive of parent study
Evaluate the long-term impact of RGX-121 on CSF Biomarkers (GAGs)
Time frame: 5 years inclusive of parent study
Long-term effect of RGX-121 on Urine Biomarker (GAGs)
Time frame: 5 years inclusive of parent study
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 19 Aug 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. This study is not recruiting at the moment.
The record lists no contact. Use the official record to reach the sponsor.
4 sites in 2 countries: see every site and its status.
Questions about this trial
What is this clinical trial studying?
An observational study of Mucopolysaccharidosis II, run by REGENXBIO Inc. at 4 sites in 2 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 2 inclusion and 1 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: under way, not looking for participants, as of the sponsor's last update on 19 Aug 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 4 sites in United States, Brazil. 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.
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?
Long-term Safety of RGX-121 (time frame: 5 years inclusive of parent study). 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 19 Aug 2026; AzTrials last refreshed its copy on 26 Oct 2026.