Metaphyseal Chondrodysplasia Research Articles

7219 Ocular Findings in Jansen Metaphyseal Chondrodysplasia

Abstract Disclosure: F. Obiezu: None. K. Pan: None. A. Ninan: None. K.L. Roszko: None. L.S. Weinstein: None. C.R. Ferreira: None. R.I. Gafni: None. T. Magone De Quadros Costa: None. M.T. Collins: None. S. Jha: None. Jansen Metaphyseal Chondrodysplasia (JMC) is an ultra-rare disorder, with only 30 patients estimated to have the disease globally. It is caused by heterozygous pathogenic variants in PTHR1 that result in constitutive activation of parathyroid hormone type 1 receptor (PTHR1) signaling. A detailed description of craniofacial manifestations of the disease is lacking. Here we characterize the ophthalmological manifestations in patients with JMC. Six patients (4 males, 67%) with genetically confirmed JMC underwent a detailed ophthalmological evaluation, spectral-domain optical coherence tomography (OCT), craniofacial CT and 18F-NaF PET/CT scans. Median age at the time of the visit was 27.5 [IQR: 29] years. On physical examination, all patients were noted to have widely spaced eyes; 5 of the 6 had down slanted palpebral fissures, proptosis, or ptosis. Two patients had incomplete or defective closure of the eyelids (lagophthalmos), of which one had a history of progressive right facial nerve palsy with profuse epiphora. The second patient had central visual field defects, bilateral moderate optic disc pallor and bilateral retinal nerve fiber layer (RNFL) atrophy on OCT exam with bilateral optic canal narrowing on CT. Notably, comparison of these findings with a prior scan performed 5 years earlier showed progressive decrease in RNFL bilaterally. This patient had a history of prolonged intravenous bisphosphonate therapy, initiated in infancy for hypercalcemia and continued for over a decade. A third patient had normal vision, subtle temporal pallor of the optic nerve heads on dilated fundus exam, normal average RNFL, but decreased retinal ganglion cell layer analysis (GCA) on OCT. GCA was decreased in 4 of the 6 patients compared to age-matched reference range indicating a chronic optic nerve atrophic process. These data represent the first comprehensive report of the ophthalmologic findings in a cohort of patients with JMC. They demonstrate that patients with JMC have significant eye findings that appear to be more prevalent and pronounced with age. This suggests age-related, progressive optic neuropathy, which can be assessed by demonstrating OCT retinal GCA and RNFL loss and, may be a feature of JMC. The benefit and effect of long-term bisphosphonate therapy in patients with JMC remains unclear. Patients with JMC should undergo regular ophthalmologic examination including optic nerve OCT, visual field testing, and craniofacial imaging. Presentation: 6/1/2024

Ocular findings in Jansen metaphyseal chondrodysplasia.

Jansen metaphyseal chondrodysplasia (JMC) is an ultra-rare disorder caused by germline heterozygous PTHR1 variants resulting in constitutive activation of parathyroid hormone type 1 receptor. A description of ocular manifestations of the disease is lacking. Six patients with JMC underwent a detailed ophthalmic evaluation, spectral-domain optical coherence tomography (OCT), visual field testing, and craniofacial CT scans. Five of 6 patients had good visual acuity. All patients had widely spaced eyes; 5/6 had downslanted palpebral fissures. One patient had proptosis, and another had bilateral ptosis. Two patients had incomplete closure of the eyelids (lagophthalmos), one had a history of progressive right facial nerve palsy with profuse epiphora, while the second had advanced optic nerve atrophy with corresponding retinal nerve fiber layer (RNFL) thinning on OCT and significant bilateral optic canal narrowing on CT scan. Additionally, this patient also had central visual field defects and abnormal color vision. A third patient had normal visual acuity, subtle temporal pallor of the optic nerve head, normal average RNFL, but decreased temporal RNFL and retinal ganglion cell layer analysis (GCA) on OCT. GCA was decreased in 4/6 patients indicating a subclinical optic nerve atrophic process. None of the patients had glaucoma or high myopia. These data represent the first comprehensive report of ophthalmic findings in JMC. Patients with JMC have significant eye findings associated with optic canal narrowing due to extensive skull base dysplastic bone overgrowth that appear to be more prevalent and pronounced with age. Progressive optic neuropathy from optic canal narrowing may be a feature of JMC, and OCT GCA can serve as a useful biomarker for progression in the setting of optic canal narrowing. We suggest that patients with JMC should undergo regular ophthalmic examination including color vision, OCT, visual field testing, orbital, and craniofacial imaging.

Altered oral microbiome, but normal human papilloma virus prevalence in cartilage-hair hypoplasia patients

BackgroundCartilage-hair hypoplasia (CHH) is a rare syndromic immunodeficiency with metaphyseal chondrodysplasia and increased risk of malignancy. In this cross-sectional observational study, we examined HPV status and oral microbiome in individuals with CHH. Oral brush samples were collected from 20 individuals with CHH (aged 5–59 years) and 41 controls (1–69 years). Alpha HPVs (43 types) were tested by nested PCR followed by bead-based probe hybridization. Separately, beta-, gamma-, mu- and nu- HPV types were investigated, and a genome-based bacterial microbiome sequencing was performed.ResultsWe found a similar alpha HPV prevalence in individuals with CHH (45%) and controls (36%). The HPV types of individuals with CHH were HPV-16 (25%), 27, 28, and 78, and of controls HPV-3, 16 (21%), 27, and 61. Beta HPV positivity and combined beta/gamma/mu/nu prevalence was detected in 11% and 11% of individuals with CHH and in 5% and 3% of the controls, respectively. Individuals with CHH differed from the controls in bacterial microbiota diversity, richness, and in microbial composition. Individuals with CHH had lower abundance of species Mitsuokella sp000469545, Parascardovia denticolens, Propionibacterium acidifaciens, UMGS1907 sp004151455, Salinicola halophilus, Haemophilus_A paraphrohaemolyticus, Fusobacterium massiliense, and Veillonella parvula, and higher abundance of Slackia exigua.ConclusionsIndividuals with CHH exhibit similar prevalence of HPV DNA but different bacterial microbiota on their oral mucosa compared to healthy controls. This may partly explain the previously observed high prevalence of oral diseases in CHH, and regular oral examination is warranted.

A Collagen10a1 mutation disrupts cell polarity in a medaka model for metaphyseal chondrodysplasia type Schmid

Heterozygous mutations in COL10A1 lead to metaphyseal chondrodysplasia type Schmid (MCDS), a skeletal disorder characterized by epiphyseal abnormalities. Prior analysis revealed impaired trimerization and intracellular retention of mutant collagen type X alpha 1 chains as cause for elevated endoplasmic reticulum (ER) stress. However, how ER stress translates into structural defects remained unclear. We generated a medaka (Oryzias latipes) MCDS model harboring a 5 base pair deletion in col10a1, which led to a frameshift and disruption of 11 amino acids in the conserved trimerization domain. col10a1Δ633a heterozygotes recapitulated key features of MCDS and revealed early cell polarity defects as cause for dysregulated matrix secretion and deformed skeletal structures. Carbamazepine, an ER stress-reducing drug, rescued this polarity impairment and alleviated skeletal defects in col10a1Δ633a heterozygotes. Our data imply cell polarity dysregulation as a potential contributor to MCDS and suggest the col10a1Δ633a medaka mutant as an attractive MCDS animal model for drug screening.

Collagen type X expression and chondrocyte hypertrophic differentiation during OA and OS development.

Chondrocyte hypertrophy and the expression of its specific marker, the collagen type X gene (COL10A1), constitute key terminal differentiation stages during endochondral ossification in long bone development. Mutations in the COL10A1 gene are known to cause schmid type metaphyseal chondrodysplasia (SMCD) and spondyloepiphyseal dyschondrodysplasia (SMD). Moreover, abnormal COL10A1 expression and aberrant chondrocyte hypertrophy are strongly correlated with skeletal diseases, notably osteoarthritis (OA) and osteosarcoma (OS). Throughout the progression of OA, articular chondrocytes undergo substantial changes in gene expression and phenotype, including a transition to a hypertrophic-like state characterized by the expression of collagen type X, matrix metalloproteinase-13, and alkaline phosphatase. This state is similar to the process of endochondral ossification during cartilage development. OS, the most common pediatric bone cancer, exhibits characteristics of abnormal bone formation alongside the presence of tumor tissue containing cartilaginous components. This observation suggests a potential role for chondrogenesis in the development of OS. A deeper understanding of the shifts in collagen X expression and chondrocyte hypertrophy phenotypes in OA or OS may offer novel insights into their pathogenesis, thereby paving the way for potential therapeutic interventions. This review systematically summarizes the findings from multiple OA models (e.g., transgenic, surgically-induced, mechanically-loaded, and chemically-induced OA models), with a particular focus on their chondrogenic and/or hypertrophic phenotypes and possible signaling pathways. The OS phenotypes and pathogenesis in relation to chondrogenesis, collagen X expression, chondrocyte (hypertrophic) differentiation, and their regulatory mechanisms were also discussed. Together, this review provides novel insights into OA and OS therapeutics, possibly by intervening the process of abnormal endochondral-like pathway with altered collagen type X expression.

Identification of a novel heterozygous PTH1R variant in a Chinese family with incomplete penetrance.

Mutations in PTH1R are associated with Jansen-type metaphyseal chondrodysplasia (JMC), Blomstrand osteochondrodysplasia (BOCD), Eiken syndrome, enchondroma, and primary failure of tooth eruption (PFE). Inheritance of the PTH1R gene can be either autosomal dominant or autosomal recessive, indicating the complexity of the gene. Our objective was to identify the phenotypic differences in members of a family with a novel PTH1R mutation. The proband was a 13-year, 6-month-old girl presenting with short stature, abnormal tooth eruption, skeletal dysplasia, and midface hypoplasia. The brother and father of the proband presented with short stature and abnormal tooth eruption. High-throughput sequencing was performed on the proband, and the variant was confirmed in the proband and other family members by Sanger sequencing. Amino acid sequence alignment was performed using ClustalX software. Three-dimensional structures were analyzed and displayed using the I-TASSER website and PyMOL software. High-throughput genome sequencing and Sanger sequencing validation showed that the proband, her father, and her brother all carried the PTH1R (NM_000316) c.1393G>A (p.E465K) mutation. The c.1393G>A (p.E465K) mutation was novel, as it has not been reported in the literature database. According to the American College of Medical Genetics and Genomics (ACMG) guidelines, the p.E465K variant was considered to have uncertain significance. Biological information analysis demonstrated that this identified variant was highly conserved and highly likely pathogenic. We identified a novel heterozygous mutation in the PTH1R gene leading to clinical manifestations with incomplete penetrance that expands the spectrum of known PTH1R mutations.

Substantially Delayed Maturation of Growth Plate Chondrocytes in "Humanized" PTH1R Mice with the H223R Mutation of Jansen's Disease.

Activating parathyroid hormone (PTH)/PTH-related Peptide (PTHrP) receptor (PTH1R) mutations causes Jansen's metaphyseal chondrodysplasia (JMC), a rare disease characterized by growth plate abnormalities, short stature, and PTH-independent hypercalcemia. Previously generated transgenic JMC mouse models, in which the human PTH1R allele with the H223R mutation (H223R-PTH1R) is expressed in osteoblasts via type Ia1 collagen or DMP1 promoters cause excess bone mass, while expression of the mutant allele via the type IIa1 collagen promoter results in only minor growth plate changes. Thus, neither transgenic JMC model adequately recapitulates the human disease. We therefore generated "humanized" JMC mice in which the H223R-PTH1R allele was expressed via the endogenous mouse Pth1r promoter and, thus, in all relevant target tissues. Founders with the H223R allele typically died within 2 months without reproducing; several mosaic male founders, however, lived longer and produced F1 H223R-PTH1R offspring, which were small and exhibited marked growth plate abnormalities. Serum calcium and phosphate levels of the mutant mice were not different from wild-type littermates, but serum PTH and P1NP were reduced significantly, while CTX-1 and CTX-2 were slightly increased. Histological and RNAscope analyses of the mutant tibial growth plates revealed markedly expanded zones of type II collagen-positive, proliferating/prehypertrophic chondrocytes, abundant apoptotic cells in the growth plate center and a progressive reduction of type X collagen-positive hypertrophic chondrocytes and primary spongiosa. The "humanized" H223R-PTH1R mice are likely to provide a more suitable model for defining the JMC phenotype and for assessing potential treatment options for this debilitating disease of skeletal development and mineral ion homeostasis. © 2023 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

A rare case of SCHMID metaphyseal chondrodysplasia associated with hypothyroidism,growth hormone deficiency and celiac disease: case report.

The authors present a rare case of 4-year-2-month-old boy referred to our Unit for harmonious short stature, he had a waddling gait, subtle micromelia, and hyperlordosis, no special facies. The skeletal scan made the diagnosis of SCHMID metaphyseal chondrodysplasia. The first laboratory workup showed elevated thyroid stimulating hormone and anti-tissue transglutaminase immunoglobulin A. The duodenal biopsies confirmed the diagnosis of coeliac disease. Treatment of levothyroxine was initiated with a gluten-free diet .6 years later, his re-evaluation showed a low insulin-like growth factor 1 and low growth hormone peaks confirming the diagnosis of growth hormone deficiency, Growth hormone therapy was initiated with an adjusted dose of levothyroxine. Other causes of short stature should not be missed when diagnosing chondrodysplasia, and further investigations should be carried out to detect other concomitant disorders since metaphyseal chondrodysplasia is a rare cause for short stature while hypothyroidism and coeliac disease are relatively common.

Clinical and molecular genetic analysis of a child with Schmid type metaphyseal chondrodysplasia

To analyze the clinical features and genotype of a child with Schmid type metaphyseal chondrodysplasia. Clinical data of the child and her parents was collected. The child was subjected to high-throughput sequencing, and candidate variant was verified by Sanger sequencing of her family members. Whole exome sequencing revealed that the child has harbored a heterozygous c.1772G>A (p.C591Y) variant of the COL10A1 gene, which was not found in either of her parents. The variant was not found in the HGMD and ClinVar databases, and was rated as likely pathogenic based on the guidelines from the American College of Medical Genetics and Genomics (ACMG). The heterozygous c.1772G>A (p.C591Y) variant of the COL10A1 gene probably underlay the Schmid type metaphyseal chondrodysplasia in this child. Genetic testing has facilitated the diagnosis and provided a basis for genetic counselling and prenatal diagnosis for this family. Above finding has also enriched the mutational spectrum of the COL10A1 gene.

Natural history and genetic spectrum of the Turkish metaphyseal dysplasia cohort, including rare types caused by biallelic COL10A1, COL2A1, and LBR variants.

Metaphyseal chondrodysplasias are a heterogeneous group of diseases characterized by short and bowed long bones and metaphyseal abnormality. The aim of this study is to investigate the genetic etiology and prognostic findings in patients with metaphyseal dysplasia. Twenty-four Turkish patients were included in this study and 13 of them were followed for 2-21years. COL10A1, RMRP sequencing and whole exome sequencing were performed. Results: Seven heterozygous pathogenic variants in COL10A1 were detected in 17 patients with Schmid type metaphyseal chondrodysplasia(MCDS). The phenotype was more severe in patients with heterozygous missense variants (one in signal peptide domain at the N-terminus of the protein, the other, class-1 group mutation at NC1 domain) compared to the patients with truncating variants. Short stature and coxa vara deformity appeared after 3 and 5years of age, respectively, while large femoral head resolved after the age of 13years in MCDS group. Interestingly, one patient with severe phenotype also had a biallelic missense variant in NC1 domain of COL10A1. Three patients with biallelic mutations in RMRP had prenatal onset short stature with short limb, and typical findings of cartilage hair hypoplasia (CHH). While immunodeficiency or recurrent infections were not observed, resistant congenital anemia was detected in one. Biallelic mutation in LBR was described in a patient with prenatal onset short stature, short and curved limb and metaphyseal abnormalities. Unlike previously reported patients, this patient had ectodermal findings, similar to CHH. A biallelic COL2A1 mutation was also found in the patient with lower limb deformities and metaphyseal involvement without vertebral and epiphyseal changes. Long-term clinical characteristics are presented in a metaphyseal dysplasia cohort, including rare types caused by biallelic COL10A1, COL2A1, and LBR variants. We also point out that the domains where mutations on COL10A1 take place are important in the genotype-phenotype relationship.

Management of proximal femur varum deformity in skeletal dysplasia: an illustrative case report

<p>Metaphyseal chondrodysplasia is skeletal dysplasia involving long tubular bones at metaphyseal regions, sparing the epiphysis, predominantly involving lower limbs, hence hindering normal mobilization activity of the individual. Individuals present with pain and deformity due to pathological fracture at the deformity site which necessitates deformity correction and surgical fixation. This is a case of skeletal metaphyseal dysplasia in 47-year female, short statured with bilateral proximal femoral Vara with pathological fracture, treated with deformity correction, surgical fixation. Patient initially presented at 36 years of age with sudden onset left hip pain. She was diagnosed with left femoral neck fracture and coxa Vara deformity. The femoral neck had spontaneously fractured due to increased bending forces acting on the femoral neck due to the coxa Vara deformity. She underwent valgus osteotomy with dynamic hip screw fixation. Further advised for prophylactic corrective osteotomy of contralateral proximal femur however patient was lost to follow-up. At 47 years she presented with pain in the right thigh. She was diagnosed to have right proximal femur pathological fracture due to progressive femur varus deformity for which she underwent right proximal femur valgus closing wedge subtrochanteric osteotomy and fixation using dynamic condylar screw. In our case left proximal femur which was operated did not have any complications. However, right proximal femur which was operated, at four months follow-up revealed no complications except for the foot drop which she developed post-surgery. Hence main aim of the study is to prove that the early prophylactic surgical management of the Vara help to provide successful outcomes.</p>

OR21-3 Spatial Signaling Bias of a Gain-of-Function PTH1R Mutant Associated with Delayed Ossification in Eiken Syndrome

Abstract Skeletal development is orchestrated by the interaction of the parathyroid hormone related peptide (PTHrP) with the parathyroid hormone receptor type 1 (PTH1R). Knock-out or severe deficiency of either PTH1R or PTHrP by homozygous loss-of-function mutations results in premature hypertrophy of chondrocytes and accelerated bone mineralization, leading to neonatal death. In contrast, patients with a heterozygous gain-of-function PTH1R mutation (H223R, T410P/R or I458K/R) present with Jansen metaphyseal chondrodysplasia (JMC), characterized by delayed bone mineralization, hypercalcemia, hypercalciuria and hypophosphatemia. Eiken syndrome is also characterized by markedly delayed bone mineralization but lacks the biochemical abnormalities of JMC. Eiken syndrome has been described for three unrelated families, in which there are one of three homozygous PTH1R mutations: R485X, E35K or Y134S. As the functional properties of these PTH1R mutants have not been studied, we assessed their characteristics in cell-based assays. GS22A cells (HEK293/Glosensor) were transiently transfected to express the WT or a mutant PTH1R. Cell surface expression levels assessed by extracellular HA tag-directed immunofluorescence flow cytometry and normalized to PTH1R-WT (100%) were 50% for PTH1R-R485X, 90% for PTH1R-E35K and 20% for PTH1R-Y134S. Dynamic cAMP measurements via the Glosensor reporter revealed that the basal activities of PTH1R-R485X and PTH1R-E35K were 7-fold and 1.5-fold higher than that of PTH1R-WT (p<0.005), while that of PTH1R-Y134S was comparable to PTH1R-WT. Stimulation with PTH(1-34) or PTHrP(1-36) yielded similar cAMP potencies for the three mutants and PTH1R-WT (EC50s ∼ 0.5 nM, p >0.05). Intracellular calcium signaling assessed by changes in FURA2 fluorescence after PTHrP(1-36) (100 nM) addition was more robust with PTH1R-R485X than for PTH1R-WT (AUCs over 2.5 mins. = 606±9 vs 551±10, p=0.0074) and similar to PTH1R-WT with PTH1R-E35K and PTH1R-Y134S (p ≥0.2). Both basal and agonist-activated cAMP signaling by the R485X mutant were reduced by addition of a dTrp12-PTHrP(7-36) antagonist/inverse agonist analog. Fluorescence microscopy of HEK293/βarrestin2YFP (GBR24) cells stimulated with TMRPTH(1-34) revealed a clear association of βarrestin2YFP with PTH1R-WT, as well as with PTH1R-E35K and PTH1R-Y134S in internalized complexes, but no such association with PTH1R-R485X. Nevertheless, over-expression of βarrestin2YFP in GS22A cells markedly reduced basal and ligand-stimulated cAMP generation by PTH1R-R485X, consistent with a residual capacity of PTH1R-485X to bind βarrestin2. Treatment with the endocytosis inhibitor Dyngo4A in GS22A cells transfected with PTH1R-R485X completely blocked TMRPTH(1-34) internalization assessed by fluorescent microscopy, and enhanced ∼5-fold the cAMP response potency to PTH(1-34) vs DMSO treatment. In contrast, treatment with Dyngo4A did not increase PTH(1-34) cAMP potency in the PTH1R-WT. Collectively these results suggest that PTH1R-R485X signals via cAMP predominantly from the cell surface. The data reveal distinct functional properties for the three PTH1R mutants associated with Eiken syndrome and suggest a novel correlation between excessive PTH1R cAMP signaling due to impaired βarrestin-mediated internalization and a delay in ossification. Presentation: Monday, June 13, 2022 11:30 a.m. - 11:45 a.m.

The effect of carbamazepine on bone structure and strength in control and osteogenesis imperfecta (Col1a2+/p.G610C) mice

The inherited brittle bone disease osteogenesis imperfecta (OI) is commonly caused by COL1A1 and COL1A2 mutations that disrupt the collagen I triple helix. This causes intracellular endoplasmic reticulum (ER) retention of the misfolded collagen and can result in a pathological ER stress response. A therapeutic approach to reduce this toxic mutant load could be to stimulate mutant collagen degradation by manipulating autophagy and/or ER‐associated degradation. Since carbamazepine (CBZ) both stimulates autophagy of misfolded collagen X and improves skeletal pathology in a metaphyseal chondrodysplasia model, we tested the effect of CBZ on bone structure and strength in 3‐week‐old male OI Col1a2 +/p.G610C and control mice. Treatment for 3 or 6 weeks with CBZ, at the dose effective in metaphyseal chondrodysplasia, provided no therapeutic benefit to Col1a2 +/p.G610C mouse bone structure, strength or composition, measured by micro‐computed tomography, three point bending tests and Fourier‐transform infrared microspectroscopy. In control mice, however, CBZ treatment for 6 weeks impaired femur growth and led to lower femoral cortical and trabecular bone mass. These data, showing the negative impact of CBZ treatment on the developing mouse bones, raise important issues which must be considered in any human clinical applications of CBZ in growing individuals.

Abstract #1178966: A Rare Case of Idiopathic Osteoporosis with COL10A1 and COL27A1 Genetic Mutations in a Premenopausal Woman

The association between bone mineral density (BMD) and fracture differs in premenopausal women when compared to the postmenopausal women. Irrespective of the BMD, any fragility fracture in those aged 20-50 requires evaluation for secondary causes of osteoporosis. In the absence of secondary causes, idiopathic osteoporosis (IOP) is considered. We present a case of a premenopausal woman with IOP whose mutational analysis revealed variants in COL10A1 and COL27A1. These genetic mutations are found in Schmid-type metaphyseal chondrodysplasia (SMCD) and Steel syndrome, respectively. To our knowledge, this is the first case report establishing a linkage between these specific mutations and IOP. A 36-year-old Hispanic woman with a history of fragility fracture of the lumbar spine at age 23 was referred to Endocrinology for further evaluation. Dual-energy x-ray absorptiometry (DEXA) reported a Z-score of -3.0 in L1-L4, consistent with osteoporosis of the lumbar spine. A careful history, physical examination, and laboratory evaluation ruled out secondary causes of osteoporosis. In the interim, the patient presented a recurrent fragility fracture of the left proximal humerus requiring surgical intervention where bone marrow (BM) was obtained for cytology. BM cytology was found normocellular without increase in blasts or lymphocytes. Notably, the mutational analysis revealed heterozygous variants of uncertain significance (VUS) in COL10A1 [variant c682 c >T (p.Pro228Ser)] and COL27A1 [variant c.1814 c >T (p.Thr 6605 Met)]. Whole exome sequencing was not able to be performed due to insurance issues. The most common secondary causes of premenopausal bone loss include estrogen deficiency as seen in hypogonadism, drug exposure such as glucocorticoids, malabsorption disorders like celiac disease, hyperthyroidism, hypercalciuria, hyperparathyroidism, and disturbances in calcium and vitamin D metabolism. Osteoporosis with no known secondary causes is known as IOP. IOP is a disorder with multiple proposed mechanisms including impairment in growth hormone and insulin like growth factor axis, osteoblast dysfunction, and genetic mutations. Mutational analysis in selected IOP cases, have shown pathogenic variants and VUS in LRP5, LRP6, COL1A1, COL1A2, PLS3, WNT1, DKK1, FKBP10, HGD, SLC34A3. Our patient was found with heterozygous VUS in COL10A1 and COL27A1. These genetic mutations are found in (SMCD) and Steel syndrome, respectively. These rare osteochondrodysplasias, more commonly found in childhood, are associated with skeletal abnormalities including scoliosis, congenital hip dislocations, short stature, and characteristic facial features. More importantly, COL10A1 encodes the alpha 1 chain of collagen type X which is involved in growth plate function, and COL27A1 gene encodes a member of the fibrillar collagen family involved in the calcification of cartilage and the transition of cartilage to bone. To our knowledge, COL10A1 and COL27A1 mutations have not been yet associated as primary causes of IOP. We report this case aiming for further research to identify additional genetic etiologies of IOP.

A Missense Mutation in COL10A1 Gene in a Pakistani Consanguineous Family with Schmid Type Metaphyseal Chondrodysplasia

A Missense Mutation in COL10A1 Gene in a Pakistani Consanguineous Family with Schmid Type Metaphyseal Chondrodysplasia

Uncovering pathways regulating chondrogenic differentiation of CHH fibroblasts

Mutations in the non-coding snoRNA component of mitochondrial RNA processing endoribonuclease (RMRP) are the cause of cartilage-hair hypoplasia (CHH). CHH is a rare form of metaphyseal chondrodysplasia characterized by disproportionate short stature and abnormal growth plate development. The process of chondrogenic differentiation within growth plates of long bones is vital for longitudinal bone growth. However, molecular mechanisms behind impaired skeletal development in CHH patients remain unclear. We employed a transdifferentiation model (FDC) combined with whole transcriptome analysis to investigate the chondrogenic transdifferentiation capacity of CHH fibroblasts and to examine pathway regulation in CHH cells during chondrogenic differentiation. We established that the FDC transdifferentiation model is a relevant in vitro model of chondrogenic differentiation, with an emphasis on the terminal differentiation phase, which is crucial for longitudinal bone growth. We demonstrated that CHH fibroblasts are capable of transdifferentiating into chondrocyte-like cells, and show a reduced commitment to terminal differentiation. We also found a number of key factors of BMP, FGF, and IGF-1 signalling axes to be significantly upregulated in CHH cells during the chondrogenic transdifferentiation. Our results support postulated conclusions that RMRP has pleiotropic functions and profoundly affects multiple aspects of cell fate and signalling. Our findings shed light on the consequences of pathological CHH mutations in snoRNA RMRP during chondrogenic differentiation and the relevance and roles of non-coding RNAs in genetic diseases in general.

M170 SHORT STATURE AND RECURRENT INFECTIONS: A CASE OF CARTILAGE-HAIR HYPOPLASIA FROM COMPOUND HETEROZYGOUS RMRP MUTATIONS

Cartilage-hair hypoplasia (CHH) is an autosomal recessive disorder characterized by metaphyseal chondrodysplasia, dwarfism, hypotrichosis, and immunodeficiency. We present a case of CHH diagnosed later in childhood and subsequently found to have two deleterious compound heterozygous mutations of the ribonuclease mitochondrial RNA-processing (RMRP) gene.

Identification of a novel COL10A1: c.1952 G>T variant in a family with Schmid metaphyseal chondrodysplasia and development of a noninvasive prenatal testing method.

BackgroundThe collagen alpha‐1(X) chain gene (COL10A1) is a known causative gene for Schmid metaphyseal chondrodysplasia (SMCD). This study clinically examined a Chinese family (n = 42) for SMCD and inheritance pattern. Fifteen individuals were diagnosed with SMCD based on characteristic skeletal phenotypes with autosomal dominant inheritance mode.MethodsFour clinically diagnosed patients and three healthy relatives were selected for subsequent genetic tests. Trio‐whole exome sequencing (Trio‐WES) followed by Sanger sequencing and familial co‐segregation analysis were performed to identify SMCD‐associated variants.Results COL10A1 (NM_000493.4):c.1952 G>T(p.Trp651Leu) variant was detected only in the four patients and not in the three healthy relatives. The variant was evaluated as “likely pathogenic” according to the American College of Medical Genetics and Genomics variation classification guidelines with evidence of PM2, PM5, PP1, and PP3. To test the presence of the target variant in proband's fetal offspring, we developed a noninvasive prenatal testing method by extracting cell‐free fetal DNA in maternal plasma followed by high‐depth sequencing. The variant was also detected in the fetus and later confirmed by amniocentesis.ConclusionWe identified a new disease‐causing variant in COL10A1. Cell‐free fetal DNA in maternal peripheral blood can be used as the rapid and noninvasive prenatal diagnostic method to detect the pathogenic/or likely pathogenic variant.

Clinical genetic characteristics of metaphyseal chondrodysplasia, McKusick type (cartilage-hair hypoplasia) in children caused by mutations in the RMRP gene: authors’ observations and literature review

Introduction. Metaphyseal chondrodysplasia, McKusick type (MCD) (OMIM: #250250) (cartilage-hair hypoplasia) is a rare, autosomal recessive disorder with main clinical manifestations including disproportionate short stature, hair thinning and hypotrichosis. Some patients with MCD develop cellular and humoral immunodeficiency, bronchiectases and Hirschsprung disease. Such patients have an increased risk of developing malignant tumors and hypoplastic anemia. MCD is one of the rare monogenic disorders caused by mutations in the RMRP gene encoding a non-coding RNA instead of a protein. So far, 123 pathogenic RMRP variants have been described. The evidence of clinical genetic correlations in patients with different types and localization of gene mutations will facilitate further understanding of pathogenetic mechanisms of the disorder and enable to predict the spectrum and severity of clinical symptoms in individual patients.Materials and methods. We present the first description of clinical genetic characteristics of two Russian patients with MCD caused by mutations in the RMRP gene, along with the comparison of our results with literature data. In both cases the diagnosis was confirmed by analyzing the RMRP gene sequence using the direct Sanger sequencing technique.Results. Analysis of specific clinical signs observed during clinical examination of our patients in comparison with those reported in literature has shown the presence of typical skeletal and extraskeletal manifestations suggestive of MCD. In Russian patients we found the major mutation previously described in the Amish and Finnish populations, n.71A>G, present in compound heterozygous state, along with two other mutations: in one patient with an earlier described n.80G>A mutation, and in the other — a newly detected n.76C>T mutation. All detected mutations were mapped to a highly conserved region of the first domain that plays a major role in the functioning of the endoribonuclease complex.Conclusions. Considering the small size of the RMRP gene and presence of specific signs of MCD, the most accurate and inexpensive method of molecular genetic analysis is the detection of mutations in the RMRP gene using direct automated Sanger sequencing. Timely diagnosis of MCD enables to choose the correct follow-up strategy for patients with this disorder.

Schmid Type Metaphyseal Chondrodysplasia in a Large Single Genetic Lineage

Several subtypes of metaphyseal chondrodysplasia exist, of which the Schmid type is the most common. Characteristics include short limbed dwarfism, coxa vara, genu vara, and waddling gait. Skull, spine, and upper extremity involvement is minimal and often nonexistent. The primary defect involves a mutation affecting the metaphyseal portion of the growth plate, while the epiphysis is normal. A large single lineage family with metaphyseal chondrodysplasia, Schmid type (MCDS) was investigated. A genetic pedigree of 135 members of this family showed autosomal dominant inheritance between all 42 affected members. The large sample size allowed for the characterization of a broad range of features present in cases of MCDS. The majority of affected patients exhibited coxa vara with an average neck/shaft angle of 105 degrees. Despite coxa vara, premature osteoarthritis of the hip is not a feature of MCDS. Genu varum is the most prevalent knee disorder in this group, but greater than 30% of patients may exhibit genu valgum. This manuscript highlights MCDS background information, differential diagnoses, treatment options, and prognosis to aid in clinical decision-making.