Functional characterization of a rare pathogenic variant c.875G > A, p.(Cys292Tyr) in COMP.

BACKGROUND: The protein encoded by the cartilage oligomeric matrix protein (COMP) gene is a noncollagenous extracellular matrix (ECM) protein that is important for chondrocyte formation and growth. Variations in the COMP gene cause pseudoachondroplasia (PSACH), which is mainly characterized by short-limbed dwarfing in the clinic. AIMS: To characterize the function of a rare pathogenic variant in the COMP gene (c.875G > A, p.Cys292Tyr). MATERIALS & METHODS: We performed 3D structural analysis, in vitro expression analysis, and immunofluorescence to characterize the effects of the variant on protein structure, expression, and cellular localization respectively. RESULTS: Variation modeling showed that the interactions between amino acids were changed after the variation, and there were 31 changes in the secondary structure of mutant COMP (MT-COMP). Western blot showed that the intracellular quantity of MT-COMP was higher than the wild-type COMP (WT-COMP). Cellular immunofluorescence results showed that WT-COMP was less abundant and homogenously distributed in cells, while the MT-COMP accumulated in the cytoplasm. DISCUSSION: Herein, we report a variant of COMP in a Chinese family with PSACH. We have shown that the rare missense variant, COMP c.875G > A, previously reported in ClinVar and identified in our patient, results in excessive accumulation of mutant protein in the cytoplasm, and is therefore pathogenic. CONCLUSION: Through in silico and experimental analyses, we provide evidence that COMP c.875G > A is the likely cause of PSACH in a Chinese family.

Health consequences of mutant cartilage oligomeric matrix protein and its relationship to abnormal growth and joint degeneration.

Cartilage oligomeric matrix protein (COMP), an extracellular matrix protein, has been shown to enhance proliferation and mechanical integrity in the matrix, supporting functions of the growth plate and articular cartilage. Mutations in COMP cause pseudoachondroplasia (PSACH), a severe dwarfing condition associated with premature joint degeneration and significant lifelong joint pain. The MT (mutant)-COMP mouse mimics PSACH with decreased limb growth, early joint degeneration and pain. Ablation of endoplasmic reticulum stress CHOP signaling eliminated pain and prevented joint degeneration. The health effects of mutant COMP are discussed in relation to cellular/chondrocyte stress in the growth plate, articular cartilage and nearby tissues, and the implications for therapeutic approaches. There are many similarities between osteoarthritis and mutant-COMP protein-induced joint degeneration, suggesting that the relevance of findings in the joints may extend beyond PSACH to idiopathic primary OA.

Juvenile toxicity study of PF-07256472/recifercept, a recombinant human soluble fibroblast growth factor receptor 3, in 2-3-month-old cynomolgus monkeys.

Achondroplasia is an autosomal disorder caused by point mutation in the gene encoding fibroblast growth factor receptor 3 (FGFR3) and resulting in gain of function. Recifercept is a potential disease modifying treatment for achondroplasia and functions as a decoy protein that competes for ligands of the mutated FGFR3. Recifercept is intended to restore normal bone growth by preventing the mutated FGFR3 from negative inhibitory signaling in pediatric patients with achondroplasia. Here we evaluated the potential effects of twice weekly administration of recifercept to juvenile cynomolgus monkeys (approximately 3-months of age at the initiation of dosing) for 6-months. No adverse effects were noted in this study, identifying the high dose as the no-observed-adverse-effect-level and supporting the use of recifercept in pediatric patients from birth. Considering that juvenile toxicity studies in nonhuman primates are not frequently conducted, and when they are conducted they typically utilize animals ≥9 months of age, this study demonstrates the feasibility of executing a juvenile toxicity study in very young monkeys prior to weaning.

Evaluation of Volumetric Bone Mineral Density, Bone Microarchitecture, and Bone Strength in Patients with Achondroplasia Caused by FGFR3 c.1138G > A Mutation.

Achondroplasia (ACH) is a skeletal disorder caused by fibroblast growth factor receptor 3 (FGFR3) variants. Volumetric bone mineral density (vBMD), bone microarchitecture, and strength have not been evaluated in these patients previously. This study aims to evaluate vBMD, bone microarchitecture, and strength in ACH patients. Seventeen patients underwent clinical and biochemical evaluations, and genetic testing. High-resolution peripheral quantitative computed tomography was performed in 10 ACH patients and 21 age- and sex-matched healthy subjects. All individuals had the hotspot mutation of c.1138G > A in FGFR3. Linear growth retardation, disproportionate short stature, and genu varum are the most common manifestations. The mean height was 108.82 ± 24.08 cm (Z score: - 5.72 ± 0.96). Total vBMD in the ACH and the control groups was 427.08 ± 49.29 mg HA/cm3 versus 300.35 ± 69.92 mg HA/cm3 (p < 0.001) at the radius and 336.90 ± 79.33 mg HA/cm3 versus 292.20 ± 62.35 mg HA/cm3 (p = 0.098) at the tibia; both at the radius and tibia, vBMD of trabecular bones was significantly lower in the ACH group than in the control group, but vBMD of cortical bones was slightly higher in the ACH group. Trabecular separation and cortical thickness in the ACH group were significantly higher than those in the control group, but trabecular number was significantly decreased in the ACH group. Stiffness and failure load were only better at the radius in the ACH group. ACH patients have higher total and cortical vBMD, lower trabecular vBMD, worse trabecular bone microarchitecture, thicker cortical bone thickness, and better estimated bone strength.

Joint Degeneration in a Mouse Model of Pseudoachondroplasia: ER Stress, Inflammation, and Block of Autophagy.

Pseudoachondroplasia (PSACH), a short limb skeletal dysplasia associated with premature joint degeneration, is caused by misfolding mutations in cartilage oligomeric matrix protein (COMP). Here, we define mutant-COMP-induced stress mechanisms that occur in articular chondrocytes of MT-COMP mice, a murine model of PSACH. The accumulation of mutant-COMP in the ER occurred early in MT-COMP articular chondrocytes and stimulated inflammation (TNFα) at 4 weeks, and articular chondrocyte death increased at 8 weeks while ER stress through CHOP was elevated by 12 weeks. Importantly, blockage of autophagy (pS6), the major mechanism that clears the ER, sustained cellular stress in MT-COMP articular chondrocytes. Degeneration of MT-COMP articular cartilage was similar to that observed in PSACH and was associated with increased MMPs, a family of degradative enzymes. Moreover, chronic cellular stresses stimulated senescence. Senescence-associated secretory phenotype (SASP) may play a role in generating and propagating a pro-degradative environment in the MT-COMP murine joint. The loss of CHOP or resveratrol treatment from birth preserved joint health in MT-COMP mice. Taken together, these results indicate that ER stress/CHOP signaling and autophagy blockage are central to mutant-COMP joint degeneration, and MT-COMP mice joint health can be preserved by decreasing articular chondrocyte stress. Future joint sparing therapeutics for PSACH may include resveratrol.

Advantages and Disadvantages of Different Treatment Methods in Achondroplasia: A Review.

Achondroplasia (ACH) is a disease caused by a missense mutation in the FGFR3 (fibroblast growth factor receptor 3) gene, which is the most common cause of short stature in humans. The treatment of ACH is necessary and urgent because untreated achondroplasia has many complications, both orthopedic and neurological, which ultimately lead to disability. This review presents the current and potential pharmacological treatments for achondroplasia, highlighting the advantages and disadvantages of all the drugs that have been demonstrated in human and animal studies in different stages of clinical trials. The article includes the potential impacts of drugs on achondroplasia symptoms other than short stature, including their effects on spinal canal stenosis, the narrowing of the foramen magnum and the proportionality of body structure. Addressing these effects could significantly improve the quality of life of patients, possibly reducing the frequency and necessity of hospitalization and painful surgical procedures, which are currently the only therapeutic options used. The criteria for a good drug for achondroplasia are best met by recombinant human growth hormone at present and will potentially be met by vosoritide in the future, while the rest of the drugs are in the early stages of clinical trials.

Typical achondroplasia secondary to a unique insertional variant of FGFR3 with in vitro demonstration of its effect on FGFR3 function.

We describe an individual in whom clinical and radiographic features are typical for achondroplasia, but in whom the common variants of FGFR3 that result in achondroplasia are absent. Whole exome sequencing demonstrated a novel, de novo 6 base pair tandem duplication in FGFR3 that results in the insertion of Ser-Phe after position Leu324. in vitro studies showed that this variant results in aberrant dimerization, excessive spontaneous phosphorylation of FGFR3 dimers and excessive, ligand-independent tyrosine kinase activity. Together, these data suggest that this variant leads to constitutive disulfide bond-mediated dimerization, and that this, surprisingly, occurs to an extent similar to the neonatal lethal thanatophoric dysplasia type I Ser249Cys variant.

In vitro and in vivo characterization of Recifercept, a soluble fibroblast growth factor receptor 3, as treatment for achondroplasia.

Achondroplasia is a rare genetic disorder caused by mutations in the Fibroblast Growth Factor receptor 3 (FGFR3). These mutations lead to aberrant increase of inhibitory signaling in proliferating chondrocytes at the growth plate. Recifercept is a potential treatment for this disease using a decoy approach to sequester FGFR3 ligands subsequently normalizing activation of the mutated FGFR3 receptor. Recifercept binds to FGF isoforms in vitro and in cellular model systems and reduces FGFR3 signaling. In addition, in a transgenic mouse model of achondroplasia, Recifercept restores reduced body weight and long bone growth in these mice. These data suggest that Recifercept treatment could lead to clinical benefits in children treated with this molecule.

Role of Signal Transduction Pathways and Transcription Factors in Cartilage and Joint Diseases.

: Osteoarthritis and rheumatoid arthritis are common cartilage and joint diseases that globally affect more than 200 million and 20 million people, respectively. Several transcription factors have been implicated in the onset and progression of osteoarthritis, including Runx2, C/EBPß, HIF2α, Sox4, and Sox11. Interleukin-1 ß (IL-1ß) leads to osteoarthritis through NF-ĸB, IκBζ, and the Zn2+-ZIP8-MTF1 axis. IL-1, IL-6, and tumor necrosis factor α (TNFα) play a major pathological role in rheumatoid arthritis through NF-ĸB and JAK/STAT pathways. Indeed, inhibitory reagents for IL-1, IL-6, and TNFα provide clinical benefits for rheumatoid arthritis patients. Several growth factors, such as bone morphogenetic protein (BMP), fibroblast growth factor (FGF), parathyroid hormone-related protein (PTHrP), and Indian hedgehog, play roles in regulating chondrocyte proliferation and differentiation. Disruption and excess of these signaling pathways cause genetic disorders in cartilage and skeletal tissues. Fibrodysplasia ossificans progressive, an autosomal genetic disorder characterized by ectopic ossification, is induced by mutant ACVR1. Mechanistic target of rapamycin kinase (mTOR) inhibitors can prevent ectopic ossification induced by ACVR1 mutations. C-type natriuretic peptide is currently the most promising therapy for achondroplasia and related autosomal genetic diseases that manifest severe dwarfism. In these ways, investigation of cartilage and chondrocyte diseases at molecular and cellular levels has enlightened the development of effective therapies. Thus, identification of signaling pathways and transcription factors implicated in these diseases is important.

Obesity in achondroplasia patients: from evidence to medical monitoring.

Achondroplasia is a rare genetic disease representing the most common form of short-limb dwarfism. It is characterized by bone growth abnormalities that are well characterized and by a strong predisposition to abdominal obesity for which causes are unknown. Despite having aroused interest at the end of the 20 h century, there are still only very little data available on this aspect of the pathology. Today, interest is rising again, and some studies are now proposing mechanistic hypotheses and guidance for patient management. These data confirm that obesity is a major health problem in achondroplasia necessitating an early yet complex clinical management. Anticipatory care should be directed at identifying children who are at high risk to develop obesity and intervening to prevent the metabolic complications in adults. In this review, we are regrouping available data characterizing obesity in achondroplasia and we are identifying the current tools used to monitor obesity in these patients.

Anthropometrics, diet, and resting energy expenditure in Norwegian adults with achondroplasia.

Individuals with achondroplasia have a high prevalence of obesity and increased risk of cardiovascular disease. Fat distribution, diet, and caloric intake are known risk factors, but the literature concerning diet and energy balance in achondroplasia is limited. The main aim of this study was to describe the anthropometrics, diet, and resting energy expenditure (REE) in a Norwegian adult achondroplasia population. Here, we present a descriptive cross-sectional study with the following variables: anthropometrics, the SmartDiet questionnaire, and dietary records. In addition, REE was measured and estimated using indirect calorimetry and prediction equations. A total of 33 adults with achondroplasia participated with a mean age of 40 years. Mean body mass index was 34.1 kg/m2 , and mean waist circumference was 94.1 cm for men and 82.2 cm for women. Their diets were classified as unhealthy (38%) or in need of improvement (62%). The mean REE values for the total group were 21 kcal/kg for the male (n = 15) and 20 kcal/kg for the female (n = 18). This study revealed a high frequency of central obesity and unhealthy dietary habits in Norwegian adults with achondroplasia. Mean energy intake was low and only 10% higher than the mean REE, and does not explain the high prevalence of abdominal obesity in our population.

TransCon CNP, a Sustained-Release C-Type Natriuretic Peptide Prodrug, a Potentially Safe and Efficacious New Therapeutic Modality for the Treatment of Comorbidities Associated with Fibroblast Growth Factor Receptor 3-Related Skeletal Dysplasias.

TransCon CNP is a C-type natriuretic peptide (CNP-38) conjugated via a cleavable linker to a polyethylene glycol carrier molecule, designed to provide sustained systemic CNP levels upon weekly subcutaneous administration. TransCon CNP is in clinical development for the treatment of comorbidities associated with achondroplasia. In both mice and cynomolgus monkeys, sustained exposure to CNP via TransCon CNP was more efficacious in stimulating bone growth than intermittent CNP exposure. TransCon CNP was well tolerated with no adverse cardiovascular effects observed at exposure levels exceeding the expected clinical therapeutic exposure. At equivalent dose levels, reductions in blood pressure and/or an increase in heart rate were seen following single subcutaneous injections of the unconjugated CNP-38 molecule or a daily CNP-39 molecule (same amino acid sequence as Vosoritide, USAN:INN). The half-life of the daily CNP-39 molecule in cynomolgus monkey was estimated to be 20 minutes, compared with 90 hours for CNP-38, released from TransCon CNP. C max for the CNP-39 molecule (20 µg/kg) was approximately 100-fold higher, compared with the peak CNP level associated with administration of 100 µg/kg CNP as TransCon CNP. Furthermore, CNP exposure for the daily CNP-39 molecule was only evident for up to 2 hours postdose (lower limit of quantification 37 pmol/l), whereas TransCon CNP gave rise to systemic exposure to CNP-38 for at least 7 days postdose. The prolonged CNP exposure and associated hemodynamically safe peak serum concentrations associated with TransCon CNP administration are suggested to improve efficacy, compared with short-lived CNP molecules, due to better therapeutic drug coverage and decreased risk of hypotension. SIGNIFICANCE STATEMENT: The hormone C-type natriuretic peptide (CNP) is in clinical development for the treatment of comorbidities associated with achondroplasia, the most common form of human dwarfism. The TransCon Technology was used to design TransCon CNP, a prodrug that slowly releases active CNP in the body over several days. Preclinical data show great promise for TransCon CNP to be an effective and well-tolerated drug that provides sustained levels of CNP in a convenient once-weekly dose, while avoiding high systemic CNP bolus concentrations that can induce cardiovascular side effects.

Suppressing UPR-dependent overactivation of FGFR3 signaling ameliorates SLC26A2-deficient chondrodysplasias.

BACKGROUND: Mutations in the SLC26A2 gene cause a spectrum of currently incurable human chondrodysplasias. However, genotype-phenotype relationships of SLC26A2-deficient chondrodysplasias are still perplexing and thus stunt therapeutic development. METHODS: To investigate the causative role of SLC26A2 deficiency in chondrodysplasias and confirm its skeleton-specific pathology, we generated and analyzed slc26a2-/- and Col2a1-Cre; slc26a2fl/fl mice. The therapeutic effect of NVP-BGJ398, an FGFR inhibitor, was tested with both explant cultures and timed pregnant females. FINDINGS: Two lethal forms of human SLC26A2-related chondrodysplasias, achondrogenesis type IB (ACG1B) and atelosteogenesis type II (AO2), are phenocopied by slc26a2-/- mice. Unexpectedly, slc26a2-/- chondrocytes are defective for collagen secretion, exhibiting intracellular retention and compromised extracellular deposition of ColII and ColIX. As a consequence, the ATF6 arm of the unfolded protein response (UPR) is preferentially triggered to overactivate FGFR3 signaling by inducing excessive FGFR3 in slc26a2-/- chondrocytes. Consistently, suppressing FGFR3 signaling by blocking either FGFR3 or phosphorylation of the downstream effector favors the recovery of slc26a2-/- cartilage cultures from impaired growth and unbalanced cell proliferation and apoptosis. Moreover, administration of an FGFR inhibitor to pregnant females shows therapeutic effects on pathological features in slc26a2-/- newborns. Finally, we confirm the skeleton-specific lethality and pathology of global SLC26A2 deletion through analyzing the Col2a1-Cre; slc26a2fl/fl mouse line. INTERPRETATION: Our study unveils a previously unrecognized pathogenic mechanism underlying ACG1B and AO2, and supports suppression of FGFR3 signaling as a promising therapeutic approach for SLC26A2-related chondrodysplasias. FUND: This work was supported by National Natural Science Foundation of China (81871743, 81730065 and 81772377).

Achondroplasia: a comprehensive clinical review.

Achondroplasia is the most common of the skeletal dysplasias that result in marked short stature (dwarfism). Although its clinical and radiologic phenotype has been described for more than 50 years, there is still a great deal to be learned about the medical issues that arise secondary to this diagnosis, the manner in which these are best diagnosed and addressed, and whether preventive strategies can ameliorate the problems that can compromise the health and well being of affected individuals. This review provides both an updated discussion of the care needs of those with achondroplasia and an exploration of the limits of evidence that is available regarding care recommendations, controversies that are currently present, and the many areas of ignorance that remain.

Cartilage oligomeric matrix protein: COMPopathies and beyond.

Cartilage oligomeric matrix protein (COMP) is a large pentameric glycoprotein that interacts with multiple extracellular matrix proteins in cartilage and other tissues. While, COMP is known to play a role in collagen secretion and fibrillogenesis, chondrocyte proliferation and mechanical strength of tendons, the complete range of COMP functions remains to be defined. COMPopathies describe pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED), two skeletal dysplasias caused by autosomal dominant COMP mutations. The majority of the mutations are in the calcium binding domains and compromise protein folding. COMPopathies are ER storage disorders in which the retention of COMP in the chondrocyte ER stimulates overwhelming cellular stress. The retention causes oxidative and inflammation processes leading to chondrocyte death and loss of long bone growth. In contrast, dysregulation of wild-type COMP expression is found in numerous diseases including: fibrosis, cardiomyopathy and breast and prostate cancers. The most exciting clinical application is the use of COMP as a biomarker for idiopathic pulmonary fibrosis and cartilage degeneration associated osteoarthritis and rheumatoid and, as a prognostic marker for joint injury. The ever expanding roles of COMP in single gene disorders and multifactorial diseases will lead to a better understanding of its functions in ECM and tissue homeostasis towards the goal of developing new therapeutic avenues.

Mutant cartilage oligomeric matrix protein (COMP) compromises bone integrity, joint function and the balance between adipogenesis and osteogenesis.

Mutations in COMP (cartilage oligomeric matrix protein) cause severe long bone shortening in mice and humans. Previously, we showed that massive accumulation of misfolded COMP in the ER of growth plate chondrocytes in our MT-COMP mouse model of pseudoachondroplasia (PSACH) causes premature chondrocyte death and loss of linear growth. Premature chondrocyte death results from activation of oxidative stress and inflammation through the CHOP-ER pathway and is reduced by removing CHOP or by anti-inflammatory or antioxidant therapies. Although the mutant COMP chondrocyte pathologic mechanism is now recognized, the effect of mutant COMP on bone quality and joint health (laxity) is largely unknown. Applying multiple analytic approaches, we describe a novel mechanism by which the deleterious consequences of mutant COMP retention results in upregulation of miR-223 disturbing the adipogenesis - osteogenesis balance. This results in reduction in bone mineral density, bone quality, mechanical strength and subchondral bone thickness. These, in addition to abnormal patterns of ossification at the ends of the femoral bones likely contribute to precocious osteoarthritis (OA) of the hips and knees in the MT-COMP mouse and PSACH. Moreover, joint laxity is compromised by abnormally thin ligaments. Altogether, these novel findings align with the PSACH phenotype of delayed ossification and bone age, extreme joint laxity and joint erosion, and extend our understanding of the underlying processes that affect bone in PSACH. These results introduce a novel finding that miR-223 is involved in the ossification defect in MT-COMP mice making it a therapeutic target.

Mutant FGFR3 associated with SADDAN disease causes cytoskeleton disorganization through PLCγ1/Src-mediated paxillin hyperphosphorylation.

K650M/E substitutions in the Fibroblast growth factor receptor 3 (FGFR3) are associated with Severe Achondroplasia with Developmental Delay and Acanthosis Nigricans (SADDAN) and Thanatophoric Dysplasia type II (TDII), respectively. Both SADDAN and TDII present with affected endochondral ossification marked by impaired chondrocyte functions and growth plate disorganization. In vitro, K650M/E substitutions confer FGFR3 constitutive kinase activity leading to impaired biosynthesis and accumulation of immature receptors in endoplasmic reticulum (ER)/Golgi. From those compartments, both SADDAN-FGFR3 and TDII-FGFR3 receptors engender uncontrolled signalling, activating PLCγ1, signal transducer and activator of transcription 1, 3 and 5 (STAT1/3/5) and ERK1/2 effectors. Here, we investigated the impact of SADDAN-FGFR3 and TDII-FGFR3 signalling on cytoskeletal organization. We report that SADDAN-FGFR3, but not TDII-FGFR3, affects F-actin organization by inducing tyrosine hyperphosphorylation of paxillin, a key regulator of focal adhesions and actin dynamics. Paxillin phosphorylation was upregulated at tyrosine 118, a functional target of Src and FAK kinases. By using Src-deficient cells and a Src kinase inhibitor, we established a role played by Src activation in paxillin hyperphosphorylation. Moreover, we found that SADDAN-FGFR3 induced FAK phosphorylation at tyrosines 576/577, suggesting its involvement as a Src co-activator in paxillin phosphorylation. Interestingly, paxillin hyperphosphorylation by SADDAN-FGFR3 caused paxillin mislocalization and partial co-localization with the mutant receptor. Finally, the SADDAN-FGFR3 double mutant unable to bind PLCγ1 failed to promote paxillin hyperphosphorylation, pointing to PLCγ1 as an early player in mediating paxillin alterations. Overall, our findings contribute to elucidate the molecular mechanism leading to cell dysfunctions caused by SADDAN-FGFR3 signalling.

The skeletal phenotype of achondrogenesis type 1A is caused exclusively by cartilage defects.

Inactivating mutations in the ubiquitously expressed membrane trafficking component GMAP-210 (encoded by Trip11) cause achondrogenesis type 1A (ACG1A). ACG1A is surprisingly tissue specific, mainly affecting cartilage development. Bone development is also abnormal, but as chondrogenesis and osteogenesis are closely coupled, this could be a secondary consequence of the cartilage defect. A possible explanation for the tissue specificity of ACG1A is that cartilage and bone are highly secretory tissues with a high use of the membrane trafficking machinery. The perinatal lethality of ACG1A prevents investigating this hypothesis. We therefore generated mice with conditional Trip11 knockout alleles and inactivated Trip11 in chondrocytes, osteoblasts, osteoclasts and pancreas acinar cells, all highly secretory cell types. We discovered that the ACG1A skeletal phenotype is solely due to absence of GMAP-210 in chondrocytes. Mice lacking GMAP-210 in osteoblasts, osteoclasts and acinar cells were normal. When we inactivated Trip11 in primary chondrocyte cultures, GMAP-210 deficiency affected trafficking of a subset of chondrocyte-expressed proteins rather than globally impairing membrane trafficking. Thus, GMAP-210 is essential for trafficking specific cargoes in chondrocytes but is dispensable in other highly secretory cells.

Constitutively-active FGFR3 disrupts primary cilium length and IFT20 trafficking in various chondrocyte models of achondroplasia.

Fibroblast growth factor receptor 3 (FGFR3) gain-of-function mutations cause dwarfisms, including achondroplasia (ACH) and thanatophoric dysplasia (TD). The constitutive activation of FGFR3 disrupts the normal process of skeletal growth. Bone-growth anomalies have been identified in skeletal ciliopathies, in which primary cilia (PC) function is disrupted. In human ACH and TD, the impact of FGFR3 mutations on PC in growth plate cartilage remains unknown. Here we showed that in chondrocytes from human (ACH, TD) and mouse Fgfr3Y367C/+ cartilage, the constitutively active FGFR3 perturbed PC length and the sorting and trafficking of intraflagellar transport (IFT) 20 to the PC. We demonstrated that inhibiting FGFR3 with FGFR inhibitor, PD173074, rescued both PC length and IFT20 trafficking. We also studied the impact of rapamycin, an inhibitor of mammalian target of rapamycin (mTOR) pathway. Interestingly, mTOR inhibition also rescued PC length and IFT20 trafficking. Together, we provide evidence that the growth plate defects ascribed to FGFR3-related dwarfisms are potentially due to loss of PC function, and these dwarfisms may represent a novel type of skeletal disorders with defective ciliogenesis.