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Study on ALXN1850 for Adolescents and Adults with Hypophosphatasia Not Previously Treated with Asfotase Alfa

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What is this trial about?

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

This clinical trial is focused on studying a rare condition called Hypophosphatasia (HPP), which affects the development of bones and teeth. The study will evaluate a treatment known as ALXN1850, a type of enzyme therapy, which is given as a solution for injection under the skin. The trial will compare the effects of ALXN1850 to a placebo in adolescents and adults who have not previously been treated with another medication called Asfotase Alfa.

The purpose of the study is to assess how well ALXN1850 works in improving physical function in participants with HPP. Participants will receive either ALXN1850 or a placebo and will be monitored over a period of time to see how their condition changes. The study will involve regular visits to the clinic for assessments and injections, and participants will be asked to perform certain physical tests to measure their progress.

This trial is designed to provide valuable information about the safety and effectiveness of ALXN1850 for people with HPP. By participating, individuals will contribute to research that may help improve treatment options for this condition in the future.

The research process

The trial runs in 5 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Joining the study

    Upon joining the study, the participant will be randomly assigned to receive either the ALXN1850 medication or a placebo. This process is double-blinded, meaning neither the participant nor the researchers will know which treatment is being administered.

  2. Step 2

    Medication administration

    The medication, ALXN1850, is administered as a subcutaneous injection. This means the solution is injected under the skin. The frequency and dosage will be determined by the study protocol and communicated to the participant at the start of the trial.

  3. Step 3

    Evaluation period

    The participant will undergo a series of assessments to evaluate the effectiveness of the treatment. These assessments include the 6-minute walk test (6MWT), which measures the distance walked in six minutes, and other functional tests such as the 30-second sit-to-stand (STS) test and the Timed Up-and-Go (TUG) test.

  4. Step 4

    Monitoring and follow-up

    Throughout the trial, the participant's health and response to the treatment will be closely monitored. This includes regular blood tests to measure plasma concentrations of certain substances and to check for any adverse effects.

  5. Step 5

    End of randomized evaluation period

    At the end of the randomized evaluation period, which is on Day 169, the participant will undergo final assessments to determine any changes from the baseline measurements. These results will help evaluate the efficacy and safety of the ALXN1850 treatment.

Who can join the trial?

10 criteria

  • The participant must be at least 12 years old on the first day of the study.
  • The participant must have a diagnosis of **Hypophosphatasia (HPP)**, which should be documented in their medical records.
  • The participant must meet one of the following genetic criteria:
    • Have a documented change in the **ALPL gene** (which can be harmful, likely harmful, or of unknown significance) from a certified laboratory.
    • Have a **PLP** level above the normal limit during the screening period, based on laboratory results.
    • The participant must meet one of the following criteria related to **ALP activity** (a type of enzyme in the blood) without any other likely cause than HPP:
      • Have a **serum ALP activity** below the normal range for their age and sex during the screening period, as measured by the central laboratory.
      • Have two documented **serum ALP activity** results, at least 15 days apart, below the normal range for their age and sex in the 24 months before the first day of the study. The laboratory must be certified.
      • The participant must have two separate **6-Minute Walk Tests (6MWTs)** showing a distance below 85% of what is expected for their age, sex, weight, and height during the screening period, without any other likely cause than HPP. Participants who need walking aids can be included.
      • Female participants who can have children and male participants must follow specific birth control requirements as outlined in the study protocol.
      • The participant or their legal representative must be able to give signed informed consent, which means they understand and agree to the study's requirements and restrictions. For adolescents, their legal guardian must provide written consent, and the adolescent must give written agreement if required.
      • The participant must not be willing or able to receive **asfotase alfa** for any reason, including not being able to follow the injection schedule for this medication.

Who cannot join the trial?

3 criteria

  • Participants who have been previously treated with **asfotase alfa**. This is a medication used to treat a condition called **hypophosphatasia**, which affects the bones.
  • Participants who are not within the specified age range for the study. The study is for adolescents and adults.
  • Participants who are part of a vulnerable population. This means people who might need special protection or care.
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Investigated drugs

ALXN1850 is a medication being studied for its effectiveness and safety in treating adolescents and adults with a condition called hypophosphatasia (HPP). This medication is a form of recombinant alkaline phosphatase, which is a type of enzyme. The trial aims to see how well ALXN1850 works in improving the physical abilities of people with HPP who have not been treated with another medication called asfotase alfa. ALXN1850 is given as an injection under the skin.

What is already known about the treatment

ALXN1850 – This medication is administered subcutaneously, meaning it is injected under the skin. It is currently being studied in clinical trials for its effectiveness and safety in treating hypophosphatasia, a rare metabolic bone disorder. The main therapeutic indication for ALXN1850 is to improve functional outcomes in adolescents and adults with this condition. At the molecular level, ALXN1850 works by providing a recombinant form of alkaline phosphatase, an enzyme that is deficient in individuals with hypophosphatasia, helping to improve bone mineralization. It is classified pharmacologically as an enzyme replacement therapy.

Investigated diseases

Hypophosphatasia – Hypophosphatasia is a rare genetic disorder that affects the development of bones and teeth. It is caused by mutations in the gene responsible for producing an enzyme called alkaline phosphatase, which is crucial for bone mineralization. As a result, individuals with this condition may experience soft and weak bones, leading to frequent fractures and skeletal abnormalities. The severity of symptoms can vary widely, ranging from mild dental issues to severe bone deformities and growth problems. In some cases, muscle weakness and pain may also be present. The progression of the disease can differ significantly among individuals, with some experiencing symptoms from infancy and others not until adulthood.
Trial detailsLast updated 7 Oct 2026
Age18+ yearsPhasePhase IIITrial ID2023-505673-32-00Protocol codeALXN1850-HPP-301Estimated enrolment122 patientsSponsorAlexion Pharmaceuticals Inc.

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