HypophosphatasiaPhase 3CHESTNUTNCT06079372
Phase 3 Study of ALXN1850 in Pediatric Participants With HPP Previously Treated With Asfotase Alfa
A Phase 3 study testing ALXN1850 and asfotase alfa in people with Hypophosphatasia, run by Alexion Pharmaceuticals, Inc. at 21 sites in 7 countries.
Trial summary
The primary purpose of this study is to assess the safety and tolerability of ALXN1850 versus asfotase alfa in pediatric participants with HPP previously treated with asfotase alfa. Read more about this study
- Who is it for?
- Ages 2 to 11 years
- Conditions the study is for
- Hypophosphatasia
- What is being tested?
- ALXN1850 and asfotase alfa
- Type of treatment
- Injection or infusion
- Could I receive a placebo?
- No, everyone receives an active treatment
- How many people
- 43 participants
- Where
- 21 sitesin 7 countries
- Study dates
- 2 Apr 2024to 29 Feb 2028
- Phase
- Phase 3
- 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 2 to 11 years
- All sexes
- No healthy volunteers
- Child
Who may be able to join
- Diagnosis of HPP documented in the medical records
- Presence of open growth plates by X-ray during Screening Period
- Tanner stage 2 or less during the Screening Period
- Must have been treated with 6 mg/kg/ week of asfotase alfa via SC injection administered as either 2mg/kg 3 times per week or 1 mg/kg 6 times per week for ≥ 6 months before Day 1. Note: participants currently treated with 9 mg/kg (eg, 3 mg/kg 3 times per week) will not be allowed in the study.
Who cannot join
- History or presence of cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrinological, hematological, neurological disorders, or any other disorders that are capable of significantly altering the absorption, metabolism, or elimination of drugs; constituting a risk when taking the study intervention; or interfering with the interpretation of data as determined by the Investigator.
- Diagnosis of primary or secondary hyperparathyroidism
- Hypoparathyroidism, unless secondary to HPP
- Any new fracture within 12 weeks before Day 1 (excluding pseudofractures)
- Planned surgical intervention which may impact the results of study assessments (in the opinion of the Investigator) during the Randomized Evaluation Period
- History of allergy or hypersensitivity to any ingredient contained in asfotase alfa or ALXN1850
- Body weight < 10 kg during the Screening Period
Trial locations and contacts
21 sites in 7 countries.
21 sites in 7 countries
United States6 sites
Research Site
Baltimore, Maryland, 21287
Research Site
Durham, North Carolina, 27705
Research Site
Hartford, Connecticut, 06106
Research Site
Kansas City, Missouri, 64108
Research Site
Minneapolis, Minnesota, 55455
Research Site
Nashville, Tennessee, 37212
Turkey (Türkiye)5 sites
Research Site
Altındağ, 06230
Research Site
Ankara, 06560
Research Site
Edirne, 22030
Research Site
Erzurum, 25240
Research Site
Istanbul, 34899
Japan4 sites
Research Site
Bunkyō City, 113-8431
Research Site
Minatoku, 105-8471
Research Site
Suita-shi, 565-0871
Research Site
Yonago-shi, 683-8504
United Kingdom3 sites
Research Site
Birmingham, B4 6NH
Research Site
Manchester
Research Site
Sheffield, S10 2TH
About this study
Official title: A Phase 3, Randomized, Open-label, Parallel-arm, Active-controlled, Multicenter Study to Evaluate Safety and Efficacy of ALXN1850 Versus Asfotase Alfa Administered Subcutaneously in Pediatric Participants (2 to < 12 Years of Age) With Hypophosphatasia (HPP) Previously Treated With Asfotase Alfa
The primary purpose of this study is to assess the safety and tolerability of ALXN1850 versus asfotase alfa in pediatric participants with HPP previously treated with asfotase alfa.
- Conditions
- Hypophosphatasia
- Being tested
- ALXN1850, asfotase alfa
- Keywords
- Hypophosphatasia, HPP, Asfotase Alfa, ALXN1850
- Medical subject headings
- Hypophosphatasia
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
ALXN1850Drug
ALXN1850 will be administered via subcutaneous (SC) injection.
asfotase alfaDrug
Asfotase alfa will be administered via SC injection.
| Study group | Role | What they receive |
|---|---|---|
| ALXN1850 | Experimental | Starting at Day 1 of the Randomized Evaluation Period participants will receive ALXN1850 for a total of 24 weeks. Participants will receive bodyweight dependent doses of either 20mg, 35mg or 50mg of ALXN1850 once q2w via SC injection. During Part A of the OLE Period, participants will have frequent visits over the first 24 weeks; Part B of the OLE Period participants will have visits every 9 months for up to approximately 108 weeks. Receives: Drug: ALXN1850; Drug: asfotase alfa |
| asfotase alfa | Experimental | Starting at Day 1 of the Randomized Evaluation Period, participants will receive asfotase alfa for a total of 24 weeks. Participants will receive 6 mg/kg/week of asfotase alfa via SC injection as either 2 mg/kg 3 times per week or 1 mg/kg 6 times per week. Part A of the OLE Period participants will have frequent visits over the first 24 weeks; Part B will have visits every 9 months for up to approximately 108 weeks. Receives: Drug: asfotase alfa |
What is being measured
The primary outcome is the main question the study is designed to answer.
Number of Participants with Treatment-emergent Adverse Events (TEAEs)
Measured: Baseline Through Day 169
Secondary outcomes (6)
Radiographic Global Impression of Change (RGI-C) Score at the end of the Randomized Evaluation Period (Day 169)
Measured: Baseline, Day 169
Change from Baseline in Rickets Severity Score (RSS) at the end of the Randomized Evaluation Period (Day 169)
Measured: Baseline, Day 169
Change from Baseline in 6-Minute Walk Test (6MWT) at the end of the Randomized Evaluation Period (Day 169)
Measured: Baseline, Day 169
Change from Baseline in Percent Predicted 6MWT at the end of the Randomized Evaluation Period (Day 169)
Measured: Baseline, Day 169
Change from Baseline in Bruininks Oseretsky Test of Motor Proficiency, Second Edition (BOT2) Score at the end of the Randomized Evaluation Period (Day 169)
Measured: Baseline, Day 169
Change from Baseline in Peabody Developmental Motor Scales, Third Edition (PDMS-3) Score at the end of the Randomized Evaluation Period (Day 169)
Measured: Baseline, Day 169
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted12 Oct 2023
- Study start2 Apr 2024
- Primary completion23 Jul 2025
- Study completion29 Feb 2028 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for HypophosphatasiaStudies of the same condition, open and under way.
- More trials run by Alexion Pharmaceuticals, Inc.The sponsor's other registered studies.
- 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
- Interventional
- Phase
- Phase 3
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Enrolment
- 43 participants (actual)
Sponsor and investigators
- Lead sponsor
- Alexion Pharmaceuticals, Inc.
- Sponsor type
- Industry (pharma, biotech, devices)
- Responsible party
- Sponsor
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06079372
- Sponsor's protocol ID
- D8590C00004
- Other IDs
- ALXN1850-HPP-303
- Acronym
- CHESTNUT
- Status last verified
- May 2026
- First submitted
- 6 Oct 2023
- Last updated
- 5 May 2026
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- Yes
- FDA-regulated device
- No
- Individual data sharing
- Yes: Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.
Study at a glance
From the registry record, last updated by the sponsor on 5 May 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- A Phase 3, Randomized, Open-label, Parallel-arm, Active-controlled, Multicenter Study to Evaluate Safety and Efficacy of ALXN1850 Versus Asfotase Alfa Administered Subcutaneously in Pediatric Participants (2 to < 12 Years of Age) With Hypophosphatasia (HPP) Previously Treated With Asfotase Alfa
- ClinicalTrials.gov ID
- NCT06079372
- Acronym / sponsor ID
- CHESTNUT / D8590C00004
- Conditions
- Hypophosphatasia
- Keywords
- Hypophosphatasia, HPP, Asfotase Alfa, ALXN1850
- Phase
- Phase 3
- Study type
- Interventional
- Recruitment status
- Active, not recruiting
- Enrolment
- 43 participants (actual)
- Lead sponsor
- Alexion Pharmaceuticals, Inc.Industry (pharma, biotech, devices)
- Study start
- 2 Apr 2024 (actual)
- Primary completion
- 23 Jul 2025 (actual)
- Study completion
- 29 Feb 2028 (estimated)
- First posted
- 12 Oct 2023 (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.
The primary purpose of this study is to assess the safety and tolerability of ALXN1850 versus asfotase alfa in pediatric participants with HPP previously treated with asfotase alfa.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 2
| Arm | Type | Receives |
|---|---|---|
| ALXN1850 | Experimental | Drug: ALXN1850, Drug: asfotase alfaStarting at Day 1 of the Randomized Evaluation Period participants will receive ALXN1850 for a total of 24 weeks. Participants will receive bodyweight dependent doses of either 20mg, 35mg or 50mg of ALXN1850 once q2w via SC injection. During Part A of the OLE Period, participants will have frequent visits over the first 24 weeks; Part B of the OLE Period participants will have visits every 9 months for up to approximately 108 weeks. |
| asfotase alfa | Experimental | Drug: asfotase alfaStarting at Day 1 of the Randomized Evaluation Period, participants will receive asfotase alfa for a total of 24 weeks. Participants will receive 6 mg/kg/week of asfotase alfa via SC injection as either 2 mg/kg 3 times per week or 1 mg/kg 6 times per week. Part A of the OLE Period participants will have frequent visits over the first 24 weeks; Part B will have visits every 9 months for up to approximately 108 weeks. |
Who may qualify
- Ages
- 2 to 11 years
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Child
Key inclusion criteria (4 listed)
- Diagnosis of HPP documented in the medical records
- Presence of open growth plates by X-ray during Screening Period
- Tanner stage 2 or less during the Screening Period
- Must have been treated with 6 mg/kg/ week of asfotase alfa via SC injection administered as either 2mg/kg 3 times per week or 1 mg/kg 6 times per week for ≥ 6 months before Day 1. Note: participants currently treated with 9 mg/kg (eg, 3 mg/kg 3 times per week) will not be allowed in the study.
Key exclusion criteria (7 listed)
- History or presence of cardiovascular, respiratory, hepatic, renal, gastrointestinal, endocrinological, hematological, neurological disorders, or any other disorders that are capable of significantly altering the absorption, metabolism, or elimination of drugs; constituting a risk when taking the study intervention; or interfering with the interpretation of data as determined by the Investigator.
- Diagnosis of primary or secondary hyperparathyroidism
- Hypoparathyroidism, unless secondary to HPP
- Any new fracture within 12 weeks before Day 1 (excluding pseudofractures)
- Planned surgical intervention which may impact the results of study assessments (in the opinion of the Investigator) during the Randomized Evaluation Period
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 |
|---|---|---|
| ALXN1850ALXN1850 will be administered via subcutaneous (SC) injection. | Drug | ALXN1850 |
| asfotase alfaAsfotase alfa will be administered via SC injection. | Drug | ALXN1850, asfotase alfa |
Primary outcome
Number of Participants with Treatment-emergent Adverse Events (TEAEs)
Time frame: Baseline Through Day 169
6 secondary outcomes
Radiographic Global Impression of Change (RGI-C) Score at the end of the Randomized Evaluation Period (Day 169)
Time frame: Baseline, Day 169
Change from Baseline in Rickets Severity Score (RSS) at the end of the Randomized Evaluation Period (Day 169)
Time frame: Baseline, Day 169
Change from Baseline in 6-Minute Walk Test (6MWT) at the end of the Randomized Evaluation Period (Day 169)
Time frame: Baseline, Day 169
Change from Baseline in Percent Predicted 6MWT at the end of the Randomized Evaluation Period (Day 169)
Time frame: Baseline, Day 169
Change from Baseline in Bruininks Oseretsky Test of Motor Proficiency, Second Edition (BOT2) Score at the end of the Randomized Evaluation Period (Day 169)
Time frame: Baseline, Day 169
Change from Baseline in Peabody Developmental Motor Scales, Third Edition (PDMS-3) Score at the end of the Randomized Evaluation Period (Day 169)
Time frame: Baseline, Day 169
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 5 May 2026.
- Individual participant dataSharing planned: Yes. Alexion has a public commitment to allow requests for access to study data and will be supplying a protocol, CSR, and plain language summaries.
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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.
21 sites in 7 countries: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 3 study testing ALXN1850 and asfotase alfa in people with Hypophosphatasia, run by Alexion Pharmaceuticals, Inc. at 21 sites in 7 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 4 inclusion and 7 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 5 May 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 21 sites in United States, Turkey (Türkiye), Japan, United Kingdom, Argentina and 2 more countries. 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.
What does this phase mean?
Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
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?
Number of Participants with Treatment-emergent Adverse Events (TEAEs) (time frame: Baseline Through Day 169). 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 5 May 2026.