Infigratinib Demonstrates Transformative Efficacy for Achondroplasia in Phase 3 PROPEL 3 Trial—With Plans to Expand into Mild Hypochondroplasia Treatment

BridgeBio Pharma has announced a significant milestone in skeletal dysplasia treatment with positive results from PROPEL 3, the pivotal Phase 3 clinical trial of infigratinib in children living with achondroplasia. This oral therapeutic marks a fundamental shift in how the most common form of disproportionate short stature is being treated, moving from injectable therapies toward a more practical daily option. As the company advances these findings toward regulatory submission, it is simultaneously accelerating development into mild hypochondroplasia and other related conditions.

Record-Breaking Growth Velocity and Body Proportionality Improvements in Phase 3 PROPEL 3 Trial

The global PROPEL 3 study, which evaluated infigratinib in children ages 3 to under 18 years with open growth plates, exceeded clinical expectations across multiple measures. The primary endpoint of annualized height velocity (AHV) showed robust superiority over placebo at Week 52, with a least squares (LS) mean treatment difference of +1.74 cm/year (p<0.0001) and a mean treatment difference of +2.10 cm/year. This represents the highest absolute AHV ever reported in a randomized trial for achondroplasia, with the infigratinib-treated group achieving 5.96 cm/year compared to 4.22 cm/year on placebo.

Beyond linear growth, the trial delivered a breakthrough that clinicians and patients have long sought: the first statistically significant improvement in body proportionality. In a pre-specified exploratory analysis of children younger than 8 years old (representing over 50% of trial participants), oral infigratinib demonstrated an LS mean decrease of -0.05 in upper-to-lower body proportionality against placebo (p<0.05). In the overall population, the treatment arm achieved an LS mean reduction of -0.05, the largest observed in any randomized achondroplasia trial to date. This metric carries profound meaning for affected families, as proportionality directly impacts physical function and self-image.

The secondary endpoint of height Z-score (using achondroplasia reference population) also confirmed efficacy, with an LS mean treatment difference of +0.32 SD (p<0.0001)—the largest Z-score difference observed in any randomized achondroplasia trial. The treatment arm itself achieved an LS mean increase of +0.41 SD, representing the largest improvement on any treatment arm in the trial history of this condition.

Strong Safety Profile with No Serious Drug-Related Adverse Events

The tolerability findings position infigratinib as a compelling alternative to existing and emerging therapies. Throughout the 52-week trial period, there were no discontinuations related to study drug and no serious adverse events attributable to the investigational therapy. Hyperphosphatemia, a known potential effect of FGFR pathway inhibition, appeared in only 3 cases (4% of participants), all of which were mild, transient, and asymptomatic—none required dose reduction or discontinuation.

Critically, no adverse events associated with FGFR1 or FGFR2 inhibition were observed, meaning ocular complications such as retinal or corneal toxicity did not emerge. Additionally, no adverse events associated with CNP analogue mechanisms (such as symptomatic hypotension, injection site reactions, or hypertrichosis) were detected, demonstrating that this mechanistically distinct approach maintains a differentiated safety window.

Clinical Significance and Quality-of-Life Implications

Ravi Savarirayan, M.D., Ph.D., of Murdoch Children’s Research Institute and the global lead investigator for PROPEL 3, emphasized that achondroplasia extends far beyond stature concerns. “Infigratinib is the first oral therapy designed to directly target FGFR3 overactivity and address the underlying cause of achondroplasia,” he noted. The improvement in proportionality is especially meaningful, as organizations like Little People of America have identified this outcome as relevant to physical function and independence—outcomes that fundamentally shape quality of life across the lifespan.

The shift from injectable CNP analogues to an orally administered small-molecule inhibitor represents a transformative practical advantage for families managing this chronic condition. Daily pill administration integrates more seamlessly into family routines than regular injections, potentially improving adherence and reducing the burden on caregivers.

Regulatory Pathway and Accelerated Development Timeline

Based on these PROPEL 3 results, BridgeBio plans to meet with regulatory authorities in the second half of 2026 to discuss submission of a New Drug Application (NDA) in the United States and a Marketing Authorization Application (MAA) in Europe. Infigratinib already holds Breakthrough Therapy Designation from the FDA for achondroplasia—a status reserved for therapies addressing serious conditions with no adequate existing treatments and demonstrating substantial improvement over current options.

The company simultaneously carries an ongoing Phase 2/3 clinical trial of infigratinib for newborns and children under 3 years old with achondroplasia, recognizing that earlier intervention may provide additional clinical benefit.

Expansion into Mild Hypochondroplasia and Related Skeletal Dysplasias

Buoyed by the PROPEL 3 data, BridgeBio is accelerating its development strategy into mild hypochondroplasia, a related genetic skeletal dysplasia caused by FGFR3 variants. The company is currently enrolling participants in the observational run-in phase for the Phase 3 trial in this indication. This expansion reflects the underlying biology: since both achondroplasia and mild hypochondroplasia stem from FGFR3 activation, a therapy targeting this pathway may address multiple conditions across the skeletal dysplasia spectrum.

The broader development vision encompasses other genetic skeletal conditions with significant unmet medical needs, signaling BridgeBio’s commitment to leveraging infigratinib’s mechanism across a family of rare genetic bone disorders.

Background: Achondroplasia as a Critical Unmet Need

Achondroplasia affects approximately 55,000 people across the United States and European Union, including up to 10,000 children and adolescents with open growth plates. The condition results from an activating variant in the FGFR3 gene, disrupting the normal regulation of bone growth. Beyond shortened stature, achondroplasia frequently leads to medical complications including obstructive sleep apnea, middle ear dysfunction, progressive kyphosis, and spinal stenosis. These comorbidities underscore why targeted therapeutic intervention—not cosmetic concern—represents a genuine medical imperative.

Prior to infigratinib’s emergence as an oral option, injectable CNP analogues represented the primary pharmacological approach under development. The introduction of an orally bioavailable FGFR3 inhibitor, combined with demonstrated efficacy and favorable tolerability, marks a pivotal moment in pediatric rare disease treatment.

BridgeBio, a biopharmaceutical company focused on genetic conditions, operates through a decentralized hub-and-spoke model designed to accelerate drug development for underserved patient populations where commercial challenges have historically limited innovation. The company’s commitment to engaging with disease communities—reflected in the co-design of clinical endpoints alongside organizations like Little People of America—exemplifies a patient-centric approach to rare disease development.