BMN 333 Versus Vosoritide in Children With Achondroplasia

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What is this study about?

This study is being done in achondroplasia, a genetic condition that causes short stature and affects how bones grow. The study compares BMN 333 with vosoritide, a medicine already used for this condition. The purpose of the study is to see how well BMN 333 works and how safe it is in children with achondroplasia.

The study has two parts. In the first part, different doses of BMN 333 are compared with vosoritide. In the second part, one selected dose of BMN 333 is compared with vosoritide. The study lasts about one year for each child after treatment starts. During the study, treatment is given as a shot under the skin, and regular checkups are done to follow the child’s growth and overall health.

The study looks at growth over time, including annual growth velocity, which means how much a child grows in one year. It also follows body measurements and checks for side effects, including changes in heart tracing tests, blood tests, and X-rays. These checks are used to help understand both the benefits and the risks of the medicines being studied.

1 study treatment begins

after joining the study, you receive BMN 333 or vosoritide by subcutaneous injection, which means an injection under the skin.

in phase 2, the study evaluates 3 doses of BMN 333 compared with vosoritide. the exact dose and timing of each study dose are not provided in the source data.

in phase 3, the study evaluates BMN 333 at one selected dose compared with vosoritide. the selected dose is not specified in the source data.

2 follow-up assessments during treatment

during treatment, your growth is measured by agv, which means annualized growth velocity, or how much growth happens over one year.

in phase 2, agv is assessed at weeks 26, 39, and 52, and the predicted agv at week 52 is evaluated based on those results.

in phase 3, agv at week 52 is evaluated.

3 other measurements during the study

your standing height, height z-score, and upper to lower body segment ratio are measured. a z-score shows how far a measurement is from the average for children of the same age and sex.

in phase 2, these measurements are checked at weeks 26 and 52.

in phase 3, these measurements are checked at week 52.

4 safety checks during the study

during the study, safety is monitored through adverse events, serious adverse events, and events of special interest. an adverse event is any health problem that happens during the study. a serious adverse event is a more severe health problem. an event of special interest is a health problem that needs special attention in the study.

the study also includes physical examinations, vital signs such as pulse and blood pressure, ecg testing, which checks the heart’s electrical activity, x-ray imaging, dxa scanning, which is a type of bone density scan, and clinical laboratory tests.

Who Can Join the Study?

Be at least 2 years old and younger than 11 years old for Phase 2, or at least 2 years old and younger than 18 years old for Phase 3, when the informed consent form is signed. Informed consent means the study permission form signed before joining.
Have achondroplasia confirmed by genetic testing, which means a laboratory test that looks at a person’s genes.
Have open epiphyses, meaning the growth plates in the bones are still open, as shown by an X-ray of the left hand using the standard medical method.
For females who are at least 10 years old or who have started menstrual periods, have a negative pregnancy test at the screening visit and be willing to have more pregnancy tests during the study.
Be in Tanner Stage I for Phase 2, or be in any Tanner stage for Phase 3. Tanner stage is a way doctors describe physical development during puberty.
Weigh at least 8.0 kg at the screening visit.
Be able to walk on their own and stand without help.
Have a caregiver who is willing to give the injections and complete the required training.

Who Cannot Join the Study?

Have a short stature condition other than achondroplasia, such as hypochondroplasia (a milder form of short stature), trisomy 21 (an extra copy of chromosome 21), pseudoachondroplasia (a bone growth disorder), or growth hormone deficiency (not enough growth hormone in the body).
Have hypothyroidism or hyperthyroidism (an underactive or overactive thyroid gland), unless it is treated.
Have diabetes mellitus (high blood sugar), unless it is considered well-controlled.
Have an autoimmune inflammatory disease (a condition where the immune system attacks the body and causes inflammation, which is swelling and irritation).
Have autonomic neuropathy (nerve damage that affects body functions you do not control, such as heart rate or digestion).
Have a history of renal insufficiency (reduced kidney function).
Have a history of cardiac disease or vascular disease (heart disease or blood vessel disease).
Have an unstable clinical condition (a health problem that is not steady or is changing in an unsafe way).
Have significant hip pathology (a serious problem with the hip joint or hip bones).

Where you can join this trial?

Verified and Recommended Sites

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Verified Sites

Site Name	City	Country	Status
Fondazione Policlinico Universitario Agostino Gemelli IRCCS	Rome	Italy
Uniwersytecki Szpital Kliniczny Im Jana Mikulicza Radeckiego We Wroclawiu	Wroclaw	Poland

Other Sites

Site Name	City	Country
IRCCS Istituto Giannina Gaslini	Genoa	Italy
Spitalul Clinic Judetean De Urgenta Craiova	Craiova	Romania
National Institute Of Endocrinology C.I. Parhon	Bucharest	Romania
Fondazione IRCCS Ca Granda Ospedale Maggiore Policlinico	Milan	Italy
Svfvsoufpzi Pobmpqfms Suoelvn Kqmtujskz Ng 1 Iybckbfypubkyrpfdl Sdtkdvn Sdisgfuip Ubgtqpyjxkfl Mqtccmpvve W Kxzajwztvr	Zabrze	Poland

Trial status

Country	Status	Recruitment Start
Italy	Not yet recruiting	06.05.2026
Poland	Not yet recruiting	06.05.2026
Romania	Not yet recruiting	06.05.2026

Trial locations

Investigated drugs:

Vosoritide

BMN 333 is the study medicine being tested in this trial. It is given as an injection under the skin. The study is looking at how well it helps children with achondroplasia grow, and how safe it is to use over time.

Vosoritide is the comparison medicine in the trial. It is also given as an injection under the skin. It is already being used for achondroplasia, and the study is comparing BMN 333 against it to see which treatment works better and how they compare in safety.

Achondroplasia – Achondroplasia is a genetic bone growth disorder that mainly affects the growth of the long bones in the arms and legs. It usually begins before birth and leads to short stature, with the upper arms and thighs more affected than the lower parts of the limbs. Children with this condition often show a larger head, a prominent forehead, and shortened fingers. The body proportions remain uneven as growth continues, and the differences in height and limb length become more noticeable over time.

Trial ID:

2025-523811-12-00

Protocol code:

333-301

Trial Phase:

Therapeutic use (Phase IV)

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BMN 333 Versus Vosoritide in Children With Achondroplasia

What is this study about?

Who Can Join the Study?

Who Cannot Join the Study?