Skip to content
Clinical Trials – home

Rare diseases

Investigational molecules

Locations

Our offerNewsroom

Not yet recruitingRare disease

Long‑term safety and tolerability of ASP2957 in boys with X‑linked myotubular myopathy

Verified siteInvestigationalNo placebo
Clinical Trials Concierge

Prefer not to search on your own, or looking for clinical trials for a rare disease? Our clinical trial advisor will do it for you.

What is this trial about?

A plain-language summary of the goals, design and what participants do

The study involves boys who have X-linked myotubular myopathy, a rare condition that makes the muscles weak and can affect breathing and movement. Participants will receive a medication called ASP2957, which is given as an intravenous infusion, meaning the drug is delivered through a needle placed into a vein.

The main goal is to see how safe the medication is when used over a long period of time. After receiving the treatment, the participants will return for regular check‑ups for several years, during which doctors will ask about any health problems, perform simple examinations, and record any changes in the need for breathing assistance.

Researchers will closely watch for side effects, serious health problems, and any issues that need special attention. They will also look at whether the amount of time a child needs help from a breathing machine changes over the study period, which helps understand how the treatment may affect daily life.

The research process

The trial runs in 6 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Enrollment and Consent

    You will be asked to sign a consent form that explains the study and confirms that you meet the eligibility criteria.

    The study staff will verify that you have previously received ASP2957 and that you have a diagnosis of X‑linked myotubular myopathy.

  2. Step 2

    Baseline Evaluation

    A series of examinations will be performed to record your current health status, including the number of hours you use ventilation support each day.

    Blood tests and other routine assessments may be done to establish a reference point for future comparisons.

  3. Step 3

    Review of Previous ASP2957 Treatment

    The study team will review the details of the ASP2957 infusion you received before joining this follow‑up study, including the method of delivery, which was an intravenous infusion (medicine given through a vein).

    No new dose of the medication will be given during this follow‑up; the focus is on observing long‑term effects.

  4. Step 4

    Scheduled Follow‑up Visits

    You will attend regular study visits, typically every six months, for up to five years after the initial infusion.

    At each visit, the staff will check for any adverse events (side effects or health problems) and record their severity.

    The amount of time you use ventilation support each day will be measured and compared with the baseline value.

    Additional laboratory tests or physical examinations may be performed as needed to monitor safety.

  5. Step 5

    Long‑Term Safety Monitoring

    Throughout the five‑year period, you are encouraged to report any new health issues, especially serious problems, to the study team.

    These reports help assess the long‑term safety and tolerability of the earlier ASP2957 treatment.

  6. Step 6

    Study Completion

    After the final scheduled visit at the end of the five‑year follow‑up, a comprehensive assessment will be performed.

    The results will be used to determine how the previous ASP2957 infusion affected safety and ventilation needs over the long term.

Who can join the trial?

4 criteria

  • Be a male patient with X‑linked myotubular myopathy who is at least 2 years old.
  • Have previously taken the study drug ASP2957 in another clinical study and now be finished with that study, have stopped it, or no longer be in contact with the study.
  • Have a parent, guardian, or other legally authorized representative give written informed consent (or, if you are old enough, give assent) to join this study.
  • Be considered a vulnerable participant, meaning special protections are used to keep you safe.
Clinical Trials Concierge

Prefer not to search on your own, or looking for clinical trials for a rare disease? Our clinical trial advisor will do it for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.

We usually reply within a few days

Verified sites

All sites with verified contact details – recruitment status may not be available; ask directly

Trial locations

Where you can join this trial

Countries are shaded by recruitment status. Click a recruiting country to ask about joining there.

Not yet recruiting
Not finding your country?

Not sure what to do next?

Joining a clinical trial can seem overwhelming. We guide you step by step, so you know exactly what to expect and how we support you through the process.

See the full process and FAQ

Investigated drugs

ASP2957 is an experimental medicine being given by intravenous infusion, which means it is delivered directly into a vein through a drip. In this study, it is tested as a possible treatment for X‑linked Myotubular Myopathy, a rare muscle disorder that affects boys. The drug is supplied as a clear liquid that can be mixed with a fluid and infused over time. The main purpose of the trial is to see how safe the medicine is when used for a long period and whether participants can tolerate it without serious side effects.

What is already known about the treatment

ASP2957 - ASP2957 is given as a sterile solution for intravenous infusion, meaning it is slowly injected into a vein over time. It is currently an investigational drug, still being studied in clinical trials and not yet approved for general medical use. The medicine is being tested for people with X‑linked myotubular myopathy, a rare muscle disease that causes severe weakness. It works by targeting the myotubularin protein pathway to improve muscle cell structure and function, and is classified as an experimental muscle‑targeting small‑molecule agent.

Investigated diseases

X-linked myotubular myopathy - A rare genetic disorder that weakens the muscles from birth, making movement and breathing difficult. The condition is caused by a mutation on the X chromosome that affects muscle cell development. Infants often have low muscle tone and may need assistance with breathing. As the child grows, muscle weakness can spread to the arms, legs, and face. The disease typically progresses slowly, with increasing difficulty in motor tasks over time.
Trial detailsLast updated 8 Nov 2026
Age0-17PhasePhase ITrial ID2025-524467-21-00Protocol code2957-CL-4001Estimated enrolment12 patientsSponsorAstellas Gene Therapies Inc.

sourced from the EU Clinical Trials Register and site verification

Want to learn more about this trial or check if you can participate?

Clinical Trials Concierge

Prefer not to search on your own, or looking for clinical trials for a rare disease? Our clinical trial advisor will do it for you.

Tell us about your condition – we search every trial in Europe and connect you with the right site.