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Study of Lonapegsomatrin and Somatropin in Children and Adolescents with Short Stature or Growth Failure due to Turner Syndrome, SHOX Deficiency, SGA, or Idiopathic Short Stature

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What is this trial about?

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

This study is being conducted to evaluate the efficacy and safety of lonapegsomatropin compared to somatropin. The research focuses on children and adolescents who experience growth failure or short stature, which means they are shorter than expected for their age. These conditions may be caused by several different disorders, such as Turner Syndrome, SHOX Deficiency, being small for gestational age, or idiopathic short stature, which is when short height occurs without a known medical cause.

Participants in the study will receive either lonapegsomatropin or somatropin through a subcutaneous injection, which is a method of delivering medication into the fatty layer just under the skin. The goal is to compare a weekly injection of the new medication to the daily use of the standard treatment. During the course of the study, height and growth progress will be monitored over a period of time to see how the different treatments affect development.

The research process

The trial runs in 3 steps – from screening to follow-up. Each step says what happens and what the team monitors.

  1. Step 1

    Study participation and medication assignment

    Upon joining the study, a group is assigned to receive either the test medication or the comparator medication.

    The test medication is lonapegsomatropin, which is administered through a subcutaneous injection, meaning it is injected into the fatty tissue just under the skin.

    The comparator medication is norditropin flexpro, which contains somatropin. this is also administered via subcutaneous injection.

  2. Step 2

    Treatment period

    If assigned lonapegsomatropin, the medication is taken once per week.

    If assigned somatropin, the medication is taken daily.

    The treatment period continues for a duration of 52 weeks to measure annualized height velocity, which is the rate of height increase over a year.

    The observation and treatment may continue up to 104 weeks to monitor long-term effects on height SDS (a score used to compare height relative to other children) and bone age (a method to determine how much a child's bones have matured).

  3. Step 3

    Safety monitoring and assessments

    During the trial, safety assessments are conducted to monitor health.

    These assessments include vital signs (such as blood pressure), physical exams, and safety labs (blood tests).

    Specific checks include fundoscopy, which is an examination of the back of the eye, and evaluations of local tolerability to see how the injection site reacts to the medication.

    bone age assessments are performed at week 52 and week 104 to track skeletal development.

Who can join the trial?

10 criteria

  • You must be at least 2 years old but younger than 18 years old at the time of the screening process.
  • You must not have previously taken growth hormone or any other treatments meant to increase growth.
  • You must be prepubertal, which means you have not yet started the physical changes associated with puberty.
  • You must have a diagnosis of Turner Syndrome, SHOX-D (a genetic condition affecting bone growth), Small for Gestational Age (being born smaller than expected for your pregnancy length), or Idiopathic Short Stature (short height with no known cause).
  • For those with Turner Syndrome or SHOX-D, the diagnosis must be confirmed by a genetic test, such as a karyotype (a test that looks at the number and structure of chromosomes) or a microarray (a detailed test to look for tiny changes in DNA).
  • For those with Turner Syndrome, if you are female, you must have a 46,XX chromosome pattern.
  • You must show signs of impaired growth, which means your height is significantly lower than the average for your age and sex based on medical growth charts.
  • For those born Small for Gestational Age, your birth weight or length must have been below a specific standard compared to other babies born at the same stage of pregnancy.
  • You must have a documented normal GH-IGF-1 axis, which means your body naturally produces the right balance of growth hormone (GH) and insulin-like growth factor 1 (IGF-1), a hormone that helps bones and tissues grow.
  • Your normal growth hormone levels must be proven through a laboratory test or a stimulation test, which is a test used to see how much growth hormone your body releases when prompted.

Who cannot join the trial?

9 criteria

  • People whose bone age (a measurement of how much a person's bones have matured compared to their actual age) is more than 20% ahead of their actual age based on X-ray results.
  • People with closed epiphyses, which means the growth plates at the ends of the bones have finished growing; this is defined as a bone age of 14 years or older for females and 16 years or older for males.
  • For those with Turner Syndrome, people who have Y chromosome material (an extra piece of genetic information usually found in males) but have not had a gonadectomy (the surgical removal of the ovaries or testes).
  • For those with Turner Syndrome, people who have less than 10% 45,X mosaicism (a condition where some cells in the body have a different number of chromosomes than others).
  • For those with Turner Syndrome, people with any known, serious cardiovascular dysfunction (problems with the heart or blood vessels) that could interfere with growth.
  • For those with Small for Gestational Age, people with chromosomal aneuploidy (an abnormal number of chromosomes), significant gene mutations (changes in the DNA that controls how the body works), or medical conditions that cause short stature, such as Laron syndrome, Noonan syndrome, or Prader-Willi syndrome.
  • For those with Small for Gestational Age, people with an absence of GH receptors (meaning the body cannot properly use growth hormone) or skeletal dysplasias (conditions that affect the development of the bones and skeleton).
  • For those with Idiopathic Short Stature, people with any known condition that causes disproportionate short stature (when limbs or body parts do not grow in proportion to each other), such as skeletal dysplasias, chromosomal aneuploidy, or specific medical syndromes like Turner syndrome, Laron syndrome, Noonan syndrome, or Prader-Willi syndrome.
  • For those with Idiopathic Short Stature, people with an abnormal SHOX-1 gene analysis (a test looking at a specific gene related to height) or an absence of GH receptors.
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Investigated drugs

  • Lonapegsomatropin

    is a medication that is being tested to see how well it works for children and adolescents with growth failure or short stature. It is administered as an injection under the skin once a week.

  • Somatropin

    is a medication used as a comparison in this study. It is a growth hormone that is administered as a daily injection under the skin.

What is already known about the treatment

  • Somatropin

    This medication is a growth hormone administered via a subcutaneous injection, typically using a pre-filled pen. It is a well-established treatment used to manage growth failure in conditions such as Turner syndrome and small for gestational age. At the molecular level, it works by binding to specific receptors on cells to stimulate growth and cell reproduction. This substance is classified as a hormone replacement therapy.

  • Lonapegsomatropin

    This medication is an experimental growth hormone provided as a powder and solvent for injection and is administered under the skin. It is currently being studied in clinical trials to treat growth failure and short stature caused by conditions like SHOX deficiency and idiopathic short stature. The drug works by attaching to growth hormone receptors to trigger essential biological growth processes, but it is modified to stay active in the body for a longer period. It is pharmacologically classified as a long-acting growth hormone.

Investigated diseases

  • Short stature homeobox containing gene deficiency

    This condition is caused by mutations in the SHOX gene, which is essential for bone growth. It typically leads to a reduction in height during childhood and adolescence. The deficiency affects the development of long bones in the arms and legs. This can result in shorter limbs compared to the rest of the body.

  • Turner syndrome

    This is a genetic condition that occurs when one of the X chromosomes is partially or completely missing in females. It often results in shorter stature and distinct physical characteristics. The condition affects various aspects of physical development throughout the growing years.

  • Idiopathic short stature

    This refers to a condition where a person is significantly shorter than average without an identifiable underlying medical cause. The growth rate is typically slower than expected for their age and sex. It is characterized by a lack of detectable hormonal or genetic abnormalities.

  • Small for gestational age

    This describes infants whose birth weight, length, or head circumference are below the expected range for their gestational age. It is a condition identified at birth reflecting growth patterns during pregnancy. These individuals may continue to show different growth velocities during early childhood.

Trial detailsLast updated 2 Oct 2026
Age0-17PhasePhase IIITrial ID2025-523079-44-00Protocol codeASND0047Estimated enrolment186 patientsSponsorAscendis Pharma Endocrinology Division A/S

sourced from the EU Clinical Trials Register and site verification

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