This page explains what clinical trials are, how they are organised in Hurler syndrome, what families and adults can expect, and how clinicians and researchers can interpret trial information in the context of existing treatments.
Research studies to answer clear questions
A clinical trial is a structured study in people designed to answer one or more focused questions, such as:
- Is this investigational therapy safe at a particular dose?
- Does it have the desired biological effect (for example increase in enzyme activity, reduction in GAGs)?
- Does it improve clinical outcomes compared with standard of care alone?
Key features:
- A written protocol reviewed by ethics committees and regulators
- Predefined inclusion and exclusion criteria
- Clear endpoints and follow-up schedules
- Independent safety monitoring
In Hurler syndrome, trials are usually run in specialised centres with multidisciplinary teams.
From early safety studies to larger outcome trials
In MPS I-H, as in other rare diseases, trials often blend traditional phases, but the basic principles are:
Phase 1 / First-in-Human
- Small number of participants
- Main focus: safety and tolerability
- May include early biological markers (enzyme activity, GAG levels)
Phase 1/2 or Phase 2
- More participants, sometimes across several centres
- Focus on safety plus signals of efficacy
- Outcomes may include organ function, imaging, growth, early neurocognitive measures
Phase 3
- Larger comparative trials where feasible, or pooled multi-centre studies
- Aim to confirm clinical benefit and support regulatory approval
In ultra-rare settings, formal “phases” can blur, but the underlying goals – safety first, then evidence of benefit – remain the same.
Eligibility and selection
Each trial has specific inclusion and exclusion criteria. These may relate to:
Diagnosis and subtype
- Confirmed MPS I with severe/Hurler phenotype
- Genetic confirmation of pathogenic IDUA variants
Age and disease stage
- Pre-symptomatic infants identified by newborn screening
- Young children before HSCT
- Children or adults post-HSCT with residual disease
- Patients who are not candidates for HSCT
Health status
- Cardiac, respiratory and neurological status
- Previous therapies (HSCT, ERT, other trials)
The aim is to recruit people for whom the risk–benefit balance is potentially favourable and in whom the study question can be answered clearly.
Endpoints in Hurler syndrome research
Trials in MPS I-H often combine several types of endpoints:
Biological / Laboratory
- Alpha-L-iduronidase activity in blood or leukocytes
- GAG or GAG-related biomarkers in blood and urine
Organ and imaging endpoints
- Cardiac function (echocardiography, valve assessment)
- Respiratory function and sleep studies
- Liver and spleen size on imaging
- Skeletal and spinal imaging, where relevant
Functional and developmental endpoints
- Growth and anthropometry
- Developmental and neurocognitive assessments in age-appropriate tools
- Measures of mobility, endurance and daily function
Patient- and family-reported outcome
- Quality of life questionnaires
- Pain, fatigue and sleep scales
- School attendance, independence and participation where applicable
The choice of endpoints depends on the therapy being studied and the aspects of unmet need it is designed to address.
How safety is protected in trials
Safety is central to all trials, especially in gene- and cell-based therapies.
Screening before enrolment
Cardiac, respiratory, infectious disease, organ function assessments
Close monitoring during and immediately after treatment
- Hospital stay around dosing for gene therapy or transplant-based approaches
- Frequent clinic visits, blood tests and imaging in the first months
Further detail from the source pages
Further detail6 sections
Long-term follow up
- For gene and cell therapy, follow up may continue for 5–10 years or more
- Monitoring for delayed effects, such as changes in liver function, immune responses or new symptoms
Oversight
- Independent Data Safety Monitoring Boards (DSMBs) review trial data
- Ethics committees and regulators can recommend protocol changes or trial suspension if safety concerns arise
Practical aspects and questions to ask
Taking part in a trial can offer access to cutting-edge therapies and close monitoring, but also involves commitment and uncertainty.
Participation may include:
- Extra hospital visits and tests beyond routine care
- Travel to a specialist centre, sometimes in another city or country
- Time away from school, work or home
- Managing unknowns about benefit and side effects
Questions you might ask your team:
- What is the main purpose of this trial?
- What has been shown in preclinical studies and, if available, earlier human studies?
- How does this compare with current standard of care for me or my child?
- What are the short- and long-term risks, and how will safety be monitored?
- What happens if we decide to withdraw from the trial?
- Will trial participation affect our access to HSCT, ERT or other treatments?
Your decision should always be voluntary and informed, with enough time and support to consider your options.
Where to look and who to ask
Because trials open and close over time, this site will not list specific active studies. Instead:
- Your specialist metabolic or transplant team is usually the best first contact.
- Recognised patient organisations for MPS and Hurler syndrome often share trial news and educational material.
- International clinical trial registries and regulatory agency websites may list authorised studies, but information can be technical.
Important reminders:
- Be cautious about information from social media or unofficial sources.
- If you hear about a trial, always discuss it with your own specialist team before making any decisions.
Further detail — part 26 sections
Evaluating study quality and relevance
When reading or presenting trial data in Hurler syndrome, useful questions include:
- Was the population appropriate to the trial’s goals (for example pre-HSCT infants vs adults with residual disease)?
- Were comparators realistic (current standard of care, contemporaneous controls, robust natural history data)?
- Are endpoints clinically meaningful, particularly regarding neurocognition, skeletal outcomes and quality of life?
- Was follow up long enough to see meaningful changes and detect late safety signals?
- How might this therapy fit within existing care pathways if it proves successful (adjunct, alternative, targeted for specific groups)?
This structured view helps align trial findings with real-world decisions and research priorities.
Protection, autonomy and transparency
Clinical trials in Hurler syndrome must follow strict ethical standards:
- Ethics committee approval for the protocol and information materials
- Age-appropriate patient and family information sheets
- Informed consent from parents or legal guardians, and assent from the child when possible
- The right to decline or withdraw from a trial at any point, without losing access to standard care
Clear explanation of:
- Data privacy and how results will be shared
- Any financial or practical support for travel and accommodation
- What will happen at the end of the trial (for example ongoing access to treatment if it helps)
Families should never feel pressured to join a trial. Saying “no” is always allowed.
Common questions about clinical trials
Does joining a trial mean we can't have HSCT or ERT?
Trials should explain clearly how investigational therapies relate to standard of care. In many cases, HSCT and/or ERT remain part of the plan.
Will my child definitely benefit?
No. By definition, trials test treatments whose benefit is not yet proven. Some participants improve; others may not.
What happens if there are side effects?
The trial team will monitor closely, treat side effects and may change or stop treatment if needed. Safety comes first.
Can we leave the trial if we change our minds?
Yes. You can withdraw at any time. The team will discuss how to do this safely and how your child’s care will continue.
Will this trial help future families?
Whatever the outcome, well-conducted trials provide knowledge that can shape better care and research for others.
Key points about clinical trials in Hurler syndrome
- Clinical trials are essential to develop better treatments for Hurler syndrome and to understand their true risks and benefits.
- Trials follow a structured pathway from early safety studies to larger outcome-focused research, guided by preclinical data and regulatory requirements.
- Participation can offer access to new therapies and intensive monitoring but also involves commitment, uncertainty and potential risks.
- Families and adults have the right to detailed information, to ask questions and to say yes or no without pressure.
- Clinicians and researchers should evaluate trials based on design quality, relevance to unmet need and alignment with current standard of care.
Research hub
Main research themes in Hurler syndrome
Further detail — part 35 sections
Translational roadmap
Steps from laboratory to clinic
Preclinical gene therapy programme
Plain language summary of systemic gene therapy studies
Rationale for gene therapy
Why systemic gene therapy is being explored
Unmet need
Residual morbidity after HSCT/ERT
Current standard of care
HSCT, ERT and multidisciplinary management