A Clinical Trial to Investigate Long-term Safety, Tolerability, and Efficacy of Weekly Subcutaneous Doses With TransCon CNP in Children and Adolescents With Achondroplasia (AttaCH)

A Phase 2, Multicenter, Long-Term, Open Label Extension Trial Evaluating Safety, Tolerability, and Efficacy of Subcutaneous Doses of TransCon CNP Administered Once Weekly in Children and Adolescents With Achondroplasia

TransCon CNP administered once-weekly in children and adolescents with achondroplasia who have completed a prior TransCon CNP clinical trial. Participants who complete a prior TransCon CNP trial and meet all eligibility criteria will be invited to continue into the long-term open label extension trial to receive 100 µg CNP/kg/week of TransCon CNP. Trial treatment will be completed when the participant reaches 16 years of age for females and 18 years of age for males and have femur and tibial epiphyseal closure. TransCon CNP treatment will continue if femur and tibial epiphyseal closure is not confirmed at the age of 16 years for females, and 18 years for males. Treatment with TransCon CNP will be completed once femur and tibial epiphyseal closure is confirmed by radiographic imaging. The trial duration is individual for each trial participant. Visits will occur every 12-14 weeks throughout the trial.

Study Overview

• Status: Enrolling by invitation
• Conditions: Achondroplasia
• Intervention / Treatment: Drug: TransCon CNP

• Study Type: Interventional
• Enrollment (Estimated): 140
• Phase: Phase 2; Phase 3

Contacts and Locations

Study Locations

• Australia
  • Victoria
    • Parkville, Victoria, Australia, 3052
      • Ascendis Pharma Investigational Site
• Austria
  • Linz, Austria, 4020
    • Ascendis Investigational Site
• Canada
  • Montreal, Canada, H3T 1C5
    • Ascendis Investigational Site
• Denmark
  • Copenhagen, Denmark, 2100
    • Ascendis Pharma Investigational Site
• Germany
  • Berlin, Germany, 13353
    • Ascendis Investigational Site
• Ireland
  • Dublin, Ireland, D01 YC76
    • Ascendis Pharma Investigational Site
• New Zealand
  • Auckland, New Zealand, 1023
    • Ascendis Investigational Site
• Portugal
  • Coimbra, Portugal, 3000-602
    • Ascendis Investigational Site
• Spain
  • Vitoria-Gasteiz, Spain, 1008
    • Ascendis Investigational Site
• United States
  • Arkansas
    • Little Rock, Arkansas, United States, 72202
      • Ascendis Pharma Investigational Site
  • Colorado
    • Aurora, Colorado, United States, 80045
      • Ascendis Investigational Site
  • Delaware
    • Wilmington, Delaware, United States, 19803
      • Ascendis Investigational Site
  • Minnesota
    • Saint Paul, Minnesota, United States, 55102
      • Ascendis Investigational Site
  • Montana
    • Columbia Falls, Montana, United States, 65212
      • Ascendis Pharma Investigational Site
  • New York
    • Buffalo, New York, United States, 14203
      • Ascendis Pharma Investigational Site
  • Texas
    • Houston, Texas, United States, 77030
      • Ascendis Investigational Site
  • Wisconsin
    • Madison, Wisconsin, United States, 53705
      • Ascendis Pharma Investigational Site

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Child
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Written, signed informed consent of the parent(s) or legal guardian(s) of the participant, and as required by the institutional review board/human research ethics committee/independent ethics committee (IRB/HREC/IEC). For participants who are below the age of consent, a written assent will be obtained in accordance with applicable requirements as required by IRB/HREC/IEC. Upon reaching the legal age of consent, depending on applicable requirements, these participants will be asked to give their own written consent.
• Participants with achondroplasia who have completed a clinical trial with TransCon CNP.
• Parent(s)/legal guardian(s) willing and able to administer weekly SC injections of TransCon CNP and to follow the protocol.
• Considered eligible based on the safety evaluations performed for evaluating stopping/holding rule criteria during the prior TransCon CNP clinical trial.

Exclusion Criteria:

• Known or suspected hypersensitivity to the investigational product or related products (trehalose, tris[hydroxymethyl]aminomethane, succinate, and methoxy polyethylene glycol [mPEG]).
• Have received any dose of prescription medications, investigational medicinal product (other than TransCon CNP).
• Sexually active female participants and female partners of male participants of childbearing potential not using a highly effective form of contraceptive (including oral, injectable, or implantable contraception, or intrauterine device (IUD)) for the entire trial period and for 90 days post end of the trial.
• Participants with serum 25-hydroxy-vitamin D (25OHD) levels of <50 nmol/L (<20 ng/mL) at Visit 1 must be on treatment regimen of Vitamin D supplementation.
• Any disease or condition that, in the opinion of the investigator, may make the participant unlikely to fully complete the trial, may confound interpretation of trial results, or may present undue risk from receiving trial treatment. This could include family situations, complications or manifestations, or medications that might impact safety or be considered confounding.

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Treatment
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: TransCon CNP 100 mcg; TransCon CNP 100 mcg delivered once weekly by subcutaneous injection	Drug: TransCon CNP; TransCon CNP drug product is a lyophilized powder in a single-use vial. Prior to use, the lyophilized powder is reconstituted with sterile water for injection and administered by subcutaneous injection via syringe and needle.

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Safety and Tolerability	Incidence of Treatment-Emergent Adverse Events	Through trial completion, an average of 10 years
Height Z-scores	Number of standard deviations	Through trial completion, an average of 10 years

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Annualized Growth Velocity	cm per year	Through trial completion, an average of 10 years

Collaborators and Investigators

• Sponsor: Ascendis Pharma Growth Disorders A/S
• Investigators: Study Director: Claus Strange, Ascendis Pharma A/S

Study record dates

Study Major Dates

• Study Start (Actual): June 21, 2023
• Primary Completion (Estimated): January 1, 2039
• Study Completion (Estimated): March 1, 2039

Study Registration Dates

• First Submitted: June 6, 2023
• First Submitted That Met QC Criteria: June 30, 2023
• First Posted (Actual): July 3, 2023

Study Record Updates

• Last Update Posted (Estimated): October 27, 2025
• Last Update Submitted That Met QC Criteria: October 24, 2025
• Last Verified: October 1, 2025

More Information

Terms related to this study

• Keywords: Achondroplasia; Dwarfism
• Additional Relevant MeSH Terms: Endocrine System Diseases; Bone Diseases; Musculoskeletal Diseases; Genetic Diseases, Inborn; Osteochondrodysplasias; Bone Diseases, Developmental; Congenital, Hereditary, and Neonatal Diseases and Abnormalities; Dwarfism; Achondroplasia
• Other Study ID Numbers: ASND0039

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: NO

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: Yes
• Studies a U.S. FDA-regulated device product: No