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Study of ALXN1850 for Children Aged 2 to 12 with Hypophosphatasia Who Have Not Previously Received Asfotase Alfa Treatment

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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, which is given as a solution for injection under the skin. The trial will compare the effects of ALXN1850 with a placebo in children aged 2 to less than 12 years 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 bone health in children with HPP. Participants will receive either ALXN1850 or a placebo through subcutaneous injections. The study will last for several months, during which the children will have regular check-ups to monitor their progress and any changes in their condition. The main focus will be on how the treatment affects the bones, as seen in X-ray images, and other health measures.

Throughout the study, the safety and effectiveness of ALXN1850 will be closely monitored. The trial aims to provide valuable information on whether ALXN1850 can be a beneficial treatment option for children with hypophosphatasia, potentially improving their quality of life by addressing the symptoms of this condition.

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

    Joining the study

    Upon joining the study, the participant must be between 2 and 12 years old and have a documented diagnosis of hypophosphatasia (HPP).

    The participant's legal guardian must provide written consent, and the participant must provide assent if applicable.

  2. Step 2

    Screening period

    During this period, the participant will undergo various assessments to confirm eligibility, including skeletal X-rays to check for HPP-related rickets and blood tests to measure serum alkaline phosphatase (ALP) activity.

    The participant must meet specific genetic or biochemical criteria related to HPP.

  3. Step 3

    Randomized evaluation period

    Participants will be randomly assigned to receive either the ALXN1850 solution for injection or a placebo. The medication is administered via subcutaneous injection.

    The treatment will continue until Day 169, with regular assessments to monitor the participant's response to the treatment.

  4. Step 4

    Primary and secondary assessments

    The primary assessment will focus on the RGI-C score at the end of the evaluation period.

    Secondary assessments will include changes in the Rickets Severity Score (RSS), physical performance tests, and quality of life measures.

  5. Step 5

    Safety monitoring

    Throughout the study, the participant will be monitored for any adverse effects related to the treatment.

    Regular blood tests and other evaluations will be conducted to ensure the participant's safety.

  6. Step 6

    End of study

    The study is expected to conclude by December 31, 2027.

    Final assessments will be conducted to evaluate the overall efficacy and safety of the treatment.

Who can join the trial?

9 criteria

  • The participant must be at least 2 years old but younger than 12 years old on the first day of the study.
  • The participant must have a diagnosis of **hypophosphatasia (HPP)**, which is a condition affecting bone development, documented in their medical records.
  • The participant must show signs of **rickets**, a bone condition, related to HPP on X-rays taken during the screening period, with a minimum **Rickets Severity Score (RSS)** of 1.0.
  • The participant must have low levels of **serum ALP (alkaline phosphatase)**, an enzyme in the blood, below the normal range for their age and sex during the screening period, as measured by a certified laboratory.
  • The participant must meet one of the following criteria:
    • Have a documented change in the **ALPL gene**, which is related to HPP, from a certified laboratory.
    • Have levels of **PLP (pyridoxal 5'-phosphate)**, a form of vitamin B6, above the normal limit during the screening period.
    • The participant must be at **Tanner stage 2** or less during the screening period. Tanner stages are used to describe physical development in children.
    • Female participants who can have children and male participants must follow specific birth control guidelines as defined in the study protocol.
    • The participant's legal guardian must be willing and able to provide written informed consent, and the participant must be willing to give written informed assent if applicable. This means agreeing to follow the study's rules and requirements.

Who cannot join the trial?

5 criteria

  • Participants who have been previously treated with a medication called asfotase alfa cannot join the study. This medication is used to treat a condition called hypophosphatasia.
  • Participants who are not within the specified age range for the study cannot participate. The study is for children, so adults cannot join.
  • Participants who have any other medical conditions that might interfere with the study or its results cannot take part.
  • Participants who are unable to follow the study procedures or instructions cannot be included.
  • Participants who are part of another clinical trial at the same time cannot join this study.
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Investigated drugs

ALXN1850 is a medication being studied for its effectiveness in treating children with hypophosphatasia, a rare bone disorder. This medication is given by injection under the skin and is being compared to a placebo to see how well it works in improving bone health in children who have not been treated with another medication called asfotase alfa.

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, specifically in a Phase 3 trial, to assess its effectiveness and safety in children aged 2 to under 12 years with hypophosphatasia, a rare bone disorder. The main therapeutic indication for ALXN1850 is to improve bone health in these pediatric patients. At the molecular level, it is designed to target and enhance bone mineralization, although the exact mechanism of action is still under investigation. ALXN1850 is classified pharmacologically as a treatment for metabolic bone diseases.

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 skeletal abnormalities and an increased risk of fractures. The severity of symptoms can vary widely, ranging from mild dental issues to severe bone deformities and growth problems. In some cases, hypophosphatasia can also affect the respiratory system and muscle strength. The progression of the disease depends on the specific genetic mutation and the age at which symptoms first appear.
Trial detailsLast updated 7 Oct 2026
Age0-17PhasePhase IIITrial ID2023-505675-73-00Protocol codeALXN1850-HPP-305Estimated enrolment47 patientsSponsorAlexion Pharmaceuticals Inc.

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