Increased classical endoplasmic reticulum stress is sufficient to reduce chondrocyte proliferation rate in the growth plate and decrease bone growth

Mutations in genes encoding cartilage oligomeric matrix protein and matrilin-3 cause a spectrum of chondrodysplasias called multiple epiphyseal dysplasia (MED) and pseudoachondroplasia (PSACH). The majority of these diseases feature classical endoplasmic reticulum (ER) stress and activation of the unfolded protein response (UPR) as a result of misfolding of the mutant protein. However, the importance and the pathological contribution of ER stress in the disease pathogenesis are unknown. The aim of this study was to investigate the generic role of ER stress and the UPR in the pathogenesis of these diseases. A transgenic mouse line (ColIITg^cog) was generated using the collagen II promoter to drive expression of an ER stress-inducing protein (Tg^cog) in chondrocytes. The skeletal and histological phenotypes of these ColIITg^cog mice were characterised. The expression and intracellular retention of Tg^cog induced ER stress and activated the UPR as characterised by increased BiP expression, phosphorylation of eIF2α and spliced Xbp1. ColIITg^cog mice exhibited decreased long bone growth and decreased chondrocyte proliferation rate. However, there was no disruption of chondrocyte morphology or growth plate architecture and perturbations in apoptosis were not apparent. Our data demonstrate that the targeted induction of ER stress in chondrocytes was sufficient to reduce the rate of bone growth, a key clinical feature associated with MED and PSACH, in the absence of any growth plate dysplasia. This study establishes that classical ER stress is a pathogenic factor that contributes to the disease mechanism of MED and PSACH. However, not all the pathological features of MED and PSACH were recapitulated, suggesting that a combination of intra- and extra-cellular factors are likely to be responsible for the disease pathology as a whole.

An anadysplasia-like, spontaneously remitting spondylometaphyseal dysplasia secondary to lamin B receptor (LBR) gene mutations: further definition of the phenotypic heterogeneity of LBR-bone dysplasias

We describe a boy who has an anadysplasia-like spondylometaphyseal dysplasia. By whole exome sequencing he was shown to have compound heterozygous mutations of LBR that codes for the lamin B receptor. He shares many similarities with a case previously described, but in whom the early natural history could not be established [Borovik et al., 2013]. Thus, in addition to Greenberg dysplasia (a perinatal lethal disorder), homozygosity or compound heterozygosity of mutations in LBR can result in a mild, spontaneously regressing bone dysplasia.

Micromelic dysplasia-like syndrome in a captive colony of common marmosets (Callithrix jacchus)

Over several years, 0% to 5% of adolescent animals in a captive colony of common marmosets (Callithrix jacchus) showed severely bended arms and legs over several years. The animals showed no pain, discomfort, or altered behavior but were unable to stretch their distal limbs to their full extent. To characterize the lesion morphologically, the bones of 4 affected marmosets were compared macroscopically and radiographically with those of 6 unaffected animals. The deformities were characterized by mid- to distal diaphyseal bending and pronounced shortening of long bones. The morphology and density of other bones including the skull and vertebrae were unaffected. Although vitamin D values were low in a fifth affected marmoset during 10 to 16 mo of age, lesions associated with rickets were not observed. To our knowledge, this report is the first to describe a micromelic dysplasia-like syndrome comprising severe, idiopathic bending and shortening of long bones in a colony of marmosets.

A novel variant in CDKN1C is associated with intrauterine growth restriction, short stature, and early-adulthood-onset diabetes

CONTEXT

CDKN1C, a cyclin-dependent kinase inhibitor and negative regulator of cellular proliferation, is paternally imprinted and has been shown to regulate β-cell proliferation. CDKN1C mutations are associated with growth disorders, including Beckwith-Wiedemann syndrome and IMAGe syndrome.

OBJECTIVE

To investigate the genetic basis for a familial disorder characterized by intrauterine growth restriction, short stature, and early-adulthood-onset diabetes.

DESIGN, SETTING, AND PARTICIPANTS

Genomic DNA samples (15 affected and 26 unaffected from a six-generation pedigree) were analyzed by genome-wide single nucleotide polymorphism arrays, whole exome and Sanger sequencing, and multiplex ligation-dependent probe amplification.

MAIN OUTCOME MEASURE(S)

Subjects were assessed for height, weight, adrenal gland size, ACTH, diabetes status, and testis volume. Linkage and sequence analyses were performed, and the identified genetic variant was functionally evaluated in reconstitution studies.

RESULTS

The pedigree followed a paternally imprinted pattern of inheritance, and genetic linkage analysis identified a single significant 2.6-megabase locus on chromosome 11p15, within the imprinting center region 2. Multiplex ligation-dependent probe amplification did not detect copy number variants or methylation abnormalities. Whole exome sequencing revealed a single novel variant in the proliferating cell nuclear antigen-binding region of CDKN1C (c.842G>T, p.R281I) that co-segregated with affected status and, unlike variants found in IMAGe, did not entirely abrogate proliferating cell nuclear antigen binding. Clinical assessments revealed that affected individuals had low testicular volume but normal adrenal function.

CONCLUSIONS

We report a novel CDKN1C mutation associated with features of IMAGe syndrome, but without adrenal insufficiency or metaphyseal dysplasia, and characterized by early-adulthood-onset diabetes. Our data expand the range of phenotypes observed with CDKN1C defects and suggest that CDKN1C mutations may represent a novel monogenic form of diabetes.

Human genetic disorders and knockout mice deficient in glycosaminoglycan

Glycosaminoglycans (GAGs) are constructed through the stepwise addition of respective monosaccharides by various glycosyltransferases and maturated by epimerases and sulfotransferases. The structural diversity of GAG polysaccharides, including their sulfation patterns and sequential arrangements, is essential for a wide range of biological activities such as cell signaling, cell proliferation, tissue morphogenesis, and interactions with various growth factors. Studies using knockout mice of enzymes responsible for the biosynthesis of the GAG side chains of proteoglycans have revealed their physiological functions. Furthermore, mutations in the human genes encoding glycosyltransferases, sulfotransferases, and related enzymes responsible for the biosynthesis of GAGs cause a number of genetic disorders including chondrodysplasia, spondyloepiphyseal dysplasia, and Ehlers-Danlos syndromes. This review focused on the increasing number of glycobiological studies on knockout mice and genetic diseases caused by disturbances in the biosynthetic enzymes for GAGs.

Biochemical defects in minor spliceosome function in the developmental disorder MOPD I

Biallelic mutations of the human RNU4ATAC gene, which codes for the minor spliceosomal U4atac snRNA, cause the developmental disorder, MOPD I/TALS. To date, nine separate mutations in RNU4ATAC have been identified in MOPD I patients. Evidence suggests that all of these mutations lead to abrogation of U4atac snRNA function and impaired minor intron splicing. However, the molecular basis of these effects is unknown. Here, we use a variety of in vitro and in vivo assays to address this question. We find that only one mutation, 124G>A, leads to significantly reduced expression of U4atac snRNA, whereas four mutations, 30G>A, 50G>A, 50G>C and 51G>A, show impaired binding of essential protein components of the U4atac/U6atac di-snRNP in vitro and in vivo. Analysis of MOPD I patient fibroblasts and iPS cells homozygous for the most common mutation, 51G>A, shows reduced levels of the U4atac/U6atac.U5 tri-snRNP complex as determined by glycerol gradient sedimentation and immunoprecipitation. In this report, we establish a mechanistic basis for MOPD I disease and show that the inefficient splicing of genes containing U12-dependent introns in patient cells is due to defects in minor tri-snRNP formation, and the MOPD I-associated RNU4ATAC mutations can affect multiple facets of minor snRNA function.

Axial correction of the lower limb deformities in a girl with anauxetic dysplasia

Valgus subtrochanteric osteotomies and hemiepiphyseodesis around the knees have been performed to correct severe coxa vara and genua valga in a girl patient who manifested extreme dwarfism associated with spondylometaepiphyseal dysplasia consistent with anauxetic dysplasia. To the best of our knowledge, this is the first description of the combined orthopaedic intervention in a girl with anauxetic dysplasia.

Pelger-huet anomaly and a mild skeletal phenotype secondary to mutations in LBR

The Lamin B receptor (LBR) gene has been described to encode a bifunctional protein. Mutations in the LBR gene can affect neutrophil segmentation and sterol reductase activity and have been associated with two different recognized clinical conditions, Pelger-Huet anomaly (PHA) and Greenberg skeletal dysplasia. PHA is a benign autosomal co-dominant laminopathy resulting in bilobed neutrophil nuclei in heterozygotes, and unsegmented (ovoid) neutrophil nuclei in homozygotes. Some putative PHA homozygotes have been reported with minor skeletal malformations. Greenberg skeletal dysplasia is a severe autosomal recessive, perinatal lethal dwarfing disorder in which heterozygous carriers are usually without clinical manifestations. We here report a girl who has bilobed neutrophil nuclei and a mild skeletal dysplasia. Mutation analysis showed two novel mutations in the LBR gene: c.651_653 delinsTGATGAGAAA (p.Ile218Aspfs*19) and c.1757G > A (p.Arg586His). These mutations were found to be in trans, and, thus, she is a compound heterozygote. Sterol analysis found trace amounts of cholesta-8,14-dien-3beta-ol, which is normally undetected in healthy individuals. This and previously reported cases suggest that mutations in LBR can result in a continuum of phenotypic manifestations.

Tracheobronchopathia osteochondroplastica--a rare or an overlooked entity?

Tracheobronchopathia osteochondroplastica is an idiopathic non-malignant disease of large airways featured by submucosal cartilaginous to osseous nodules overlying the cartilaginous rings, which may be focal or diffuse. Clinical presentation varies from asymptomatic to symptoms like breathlessness, recurrent chest infections, cough and hemoptysis. Due to the lack of awareness of this disease, it remains an under recognized entity. We are describing the computed tomography and bronchoscopic findings of two recently diagnosed cases at our institute. The purpose of this report is to familiarize radiologists with imaging appearance of this condition, with the goal of increasing clinical suspicion of this uncommon condition.

Partial deletion of the sulfate transporter SLC13A1 is associated with an osteochondrodysplasia in the Miniature Poodle breed

A crippling dwarfism was first described in the Miniature Poodle in Great Britain in 1956. Here, we resolve the genetic basis of this recessively inherited disorder. A case-control analysis (8:8) of genotype data from 173 k SNPs revealed a single associated locus on CFA14 (P(raw) <10(-8)). All affected dogs were homozygous for an ancestral haplotype consistent with a founder effect and an identical-by-descent mutation. Systematic failure of nine, nearly contiguous SNPs, was observed solely in affected dogs, suggesting a deletion was the causal mutation. A 130-kb deletion was confirmed both by fluorescence in situ hybridization (FISH) analysis and by cloning the physical breakpoints. The mutation was perfectly associated in all cases and obligate heterozygotes. The deletion ablated all but the first exon of SLC13A1, a sodium/sulfate symporter responsible for regulating serum levels of inorganic sulfate. Our results corroborate earlier findings from an Slc13a1 mouse knockout, which resulted in hyposulfatemia and syndromic defects. Interestingly, the metabolic disorder in Miniature Poodles appears to share more clinical signs with a spectrum of human disorders caused by SLC26A2 than with the mouse Slc13a1 model. SLC26A2 is the primary sodium-independent sulfate transporter in cartilage and bone and is important for the sulfation of proteoglycans such as aggregan. We propose that disruption of SLC13A1 in the dog similarly causes undersulfation of proteoglycans in the extracellular matrix (ECM), which impacts the conversion of cartilage to bone. A co-dominant DNA test of the deletion was developed to enable breeders to avoid producing affected dogs and to selectively eliminate the mutation from the gene pool.

Identification of the first ATRIP-deficient patient and novel mutations in ATR define a clinical spectrum for ATR-ATRIP Seckel Syndrome

A homozygous mutational change in the Ataxia-Telangiectasia and RAD3 related (ATR) gene was previously reported in two related families displaying Seckel Syndrome (SS). Here, we provide the first identification of a Seckel Syndrome patient with mutations in ATRIP, the gene encoding ATR-Interacting Protein (ATRIP), the partner protein of ATR required for ATR stability and recruitment to the site of DNA damage. The patient has compound heterozygous mutations in ATRIP resulting in reduced ATRIP and ATR expression. A nonsense mutational change in one ATRIP allele results in a C-terminal truncated protein, which impairs ATR-ATRIP interaction; the other allele is abnormally spliced. We additionally describe two further unrelated patients native to the UK with the same novel, heterozygous mutations in ATR, which cause dramatically reduced ATR expression. All patient-derived cells showed defective DNA damage responses that can be attributed to impaired ATR-ATRIP function. Seckel Syndrome is characterised by microcephaly and growth delay, features also displayed by several related disorders including Majewski (microcephalic) osteodysplastic primordial dwarfism (MOPD) type II and Meier-Gorlin Syndrome (MGS). The identification of an ATRIP-deficient patient provides a novel genetic defect for Seckel Syndrome. Coupled with the identification of further ATR-deficient patients, our findings allow a spectrum of clinical features that can be ascribed to the ATR-ATRIP deficient sub-class of Seckel Syndrome. ATR-ATRIP patients are characterised by extremely severe microcephaly and growth delay, microtia (small ears), micrognathia (small and receding chin), and dental crowding. While aberrant bone development was mild in the original ATR-SS patient, some of the patients described here display skeletal abnormalities including, in one patient, small patellae, a feature characteristically observed in Meier-Gorlin Syndrome. Collectively, our analysis exposes an overlapping clinical manifestation between the disorders but allows an expanded spectrum of clinical features for ATR-ATRIP Seckel Syndrome to be defined.

Metaphyseal chondromatosis combined with D-2-hydroxyglutaric aciduria in four patients

We report four patients who presented with a severe form of metaphyseal chondromatosis in association with D-2-hydroxyglutaric aciduria (D-2-HGA). All patients showed splaying columns of irregular ossification defects with bulbous metaphyses of the long tubular bones, as well as remarkable involvement of the short tubular and flat bones. The vertebral bodies revealed platyspondyly with irregular, stippled endplates. D-2-HGA has been described as a neurometabolic disorder manifesting a broad range of impairment in mental and motor development. Although hydroxyglutaric acid was excreted in high amounts in the urine of all four patients described herein, no significant neurologic abnormalities were evident. This unusual combination of characteristic skeletal and metabolic abnormalities has rarely been reported. Thus, our report will facilitate the recognition of this distinctive entity, and we suggest that a urine organic acid screening be obtained in patients who present with generalized enchondromatosis.

Dysmorphic facies and diffuse posterior spine ankylosis in a patient with unusual form of spondyloenchondrodysplasia (Spranger type IV)

We describe a male patient, who was seen for the first time at the age of 8 years because of short trunk dwarfism. Spine radiographs showed platyspondyly with irregular areas of increased and decreased mineralization (irregular spotted appearance within lytic lesions located along the posterior vertebral bodies of the entire spine). Skeletal survey showed no enchondromatous lesions of the short/long tubular bones. At the age of 17, progressive spine stiffness associated with stooping posture developed. 3DCT scanning showed pathological transformation of the spinal enchondromas into generalized ossification and thickening of the posterior vertebral elements (vertebral laminae, supraspinal, and interspinal ligaments, respectively) causing effectively the development of a diffuse posterior spinal ankylosis. We report what might be a unique subtype of spondyloenchondrodysplasia (Spranger type IV).

Acrodysostosis

Acrodysostosis refers to a group of rare skeletal dysplasias that share in common characteristic clinical and radiological features including brachydactyly, facial dysostosis, and nasal hypoplasia. In the past, the term acrodysostosis has been used to describe patients with heterogeneous phenotypes, including, in some cases, patients that today would be given alternative diagnoses. The recent finding that mutations impairing the cAMP binding to PRKAR1A are associated with "typical" acrodysostosis and hormonal resistance initiates the era where this group of disorders can be categorized on a genetic basis. In this review, we will first discuss the clinical, radiologic, and metabolic features of acrodysostosis, emphasizing evidence that several forms of the disease are likely to exist. Second, we will describe recent results explaining the pathogenesis of acrodysostosis with hormonal resistance (ADOHR). Finally, we will discuss the similarities and differences observed comparing patients with ADOHR and other diseases resulting from defects in the PTHR1 signaling pathway, in particular, pseudohypoparathyroidism type 1a and pseudopseudohypoparathyroidism.

[Clinical analysis of four patients with Schwartz-Jampel syndrome]

OBJECTIVE

To analyze the clinical manifestation, diagnosis and treatment of Schwartz-Jampel syndrome (SJS).

METHOD

The clinical data, including demographic, laboratory tests (creatase, creatine kinase, etc.) and electromyography of 4 children with SJS were analyzed.

RESULT

All the 4 patients were male. The age of onset was from 0.5 to 1.25 years (average 0.83 years). The onset of 4 patients was insidious, the age to see doctor was from 2.17 to 10 years (average 5.92 years), body height was less than the third percentile rank in the children of same age and gender, they presented with facial expression stiffness, microstomia, difficult in opening mouth, blepharophimosis, limbs stiffness and, so formed a characteristic phenotype. Investigations showed the creatase in serum increased, creatine kinase (CK): 229 - 1039 U/L (normal value < 200 U/L), Creatine Kinase MB (CK-MB): 30 - 45 U/L (normal value < 25 U/L), lactate dehydrogenase (LDH): 455 - 716 U/L (normal value < 240 U/L). General myotonia potential was found in electromyography, osteoarticular deformities in medical imaging, and muscle biopsy in 2 patients showed type I muscle fibers differed in size and were disproportionate. All the patients took oral vitamin B, and received rehabilitation training, 1 patient took carbamazepine for 1 month, blepharophimosis and limbs stiffness was improved.

CONCLUSION

SJS is a rare autosomal recessive inherited disease. Clinical manifestations of SJS are characteristic facies, skeletal abnormalities, generous myotonia and short stature. Carbamazepine is effective for treatment.

Transcriptional profiling of chondrodysplasia growth plate cartilage reveals adaptive ER-stress networks that allow survival but disrupt hypertrophy

Metaphyseal chondrodysplasia, Schmid type (MCDS) is characterized by mild short stature and growth plate hypertrophic zone expansion, and caused by collagen X mutations. We recently demonstrated the central importance of ER stress in the pathology of MCDS by recapitulating the disease phenotype by expressing misfolding forms of collagen X (Schmid) or thyroglobulin (Cog) in the hypertrophic zone. Here we characterize the Schmid and Cog ER stress signaling networks by transcriptional profiling of microdissected mutant and wildtype hypertrophic zones. Both models displayed similar unfolded protein responses (UPRs), involving activation of canonical ER stress sensors and upregulation of their downstream targets, including molecular chaperones, foldases, and ER-associated degradation machinery. Also upregulated were the emerging UPR regulators Wfs1 and Syvn1, recently identified UPR components including Armet and Creld2, and genes not previously implicated in ER stress such as Steap1 and Fgf21. Despite upregulation of the Chop/Cebpb pathway, apoptosis was not increased in mutant hypertrophic zones. Ultrastructural analysis of mutant growth plates revealed ER stress and disrupted chondrocyte maturation throughout mutant hypertrophic zones. This disruption was defined by profiling the expression of wildtype growth plate zone gene signatures in the mutant hypertrophic zones. Hypertrophic zone gene upregulation and proliferative zone gene downregulation were both inhibited in Schmid hypertrophic zones, resulting in the persistence of a proliferative chondrocyte-like expression profile in ER-stressed Schmid chondrocytes. Our findings provide a transcriptional map of two chondrocyte UPR gene networks in vivo, and define the consequences of UPR activation for the adaptation, differentiation, and survival of chondrocytes experiencing ER stress during hypertrophy. Thus they provide important insights into ER stress signaling and its impact on cartilage pathophysiology.

Tracheobronchopathia osteochondroplastica presenting as a single dominant tracheal mass

Tracheobronchopathia osteochondroplastica is a rare, benign disorder of upper airways characterized by multiple submucosal metaplastic cartilaginous and bony nodules arising from the tracheal cartilage. We report an unusual presentation of tracheobronchopathia osteochondroplastica as a single dominant nodule arising from the anterior tracheal rings in a young adult man who presented with wheezing and symptoms of airway obstruction. The differential diagnosis of cartilaginous and bony endotracheal lesions is discussed.

Increased basal activity is a key determinant in the severity of human skeletal dysplasia caused by TRPV4 mutations

TRPV4 is a mechanically activated Ca²⁺-passing channel implicated in the sensing of forces, including those acting on bones. To date, 33 mutations are known to affect human bone development to different extents. The spectrum of these skeletal dysplasias (SD) ranges from dominantly inherited mild brachylomia (BO) to neonatal lethal forms of metatropic dysplasia (MD). Complexities of the results from fluorescence and electrophysiological studies have led to questions on whether channel activity is a good predictor of disease severity. Here we report on a systematic examination of 14 TRPV4 mutant alleles covering the entire SD spectrum. Expressed in Xenopus oocyte and without any stimulation, the wild-type channel had a ∼1% open probability (Po) while those of most of the lethal MD channels approached 100%. All mutant channels had higher basal open probabilities, which limited their further increase by agonist or hypotonicity. The magnitude of this limitation revealed a clear correlation between the degree of over-activity (the molecular phenotype) and the severity of the disease over the entire spectrum (the biological phenotype). Thus, while other factors are at play, our results are consistent with the increased TRPV4 basal activity being a critical determinant of the severity of skeletal dysplasia. We discuss how the channel over-activity may lead to the “gain-of-function” phenotype and speculate that the function of wild-type TRPV4 may be secondary in normal bone development but crucial in an acute process such as fracture repair in the adult.

The jumping SHOX gene--crossover in the pseudoautosomal region resulting in unusual inheritance of Leri-Weill dyschondrosteosis

CONTEXT

During meiosis I, the recombination frequency in the pseudoautosomal region on Xp and Yp (PAR1) in males is very high. As a result, mutated genes located within the PAR1 region can be transferred from the Y-chromosome to the X-chromosome and vice versa.

PATIENTS

Here we describe three families with SHOX abnormalities resulting in Leri-Weill dyschondrosteosis or Langer mesomelic dysplasia.

RESULTS

In about half of the segregations investigated, a transfer of the SHOX abnormality to the alternate sex chromosome was demonstrated.

CONCLUSIONS

Patients with an abnormality of the SHOX gene should receive genetic counseling as to the likelihood that they may transmit the mutation or deletion to a son as well as to a daughter.

New phenotype with generalized platyspondyly, large mandible, hypoplastic teeth, strabismus, hyperopia and low cholesterol levels

A sporadic, adult male patient with generalized platyspondyly, large mandible, hypoplastic teeth, strabismus, and low serum cholesterol levels is presented. Some of the patient's features resemble brachyolmia, Spondylo-epiphyseal dysplasia tarda, Kenny-Caffey and Stickler syndromes. Based on literature review, possible diagnoses are discussed. In conclusion, this patient can have a variant of brachyolmia or Spondylo-epiphyseal dysplasia tarda. However, we cannot exclude that this constellation of clinical features may represent a new syndrome.

Fibrochondrogenesis results from mutations in the COL11A1 type XI collagen gene

Fibrochondrogenesis is a severe, autosomal-recessive, short-limbed skeletal dysplasia. In a single case of fibrochondrogenesis, whole-genome SNP genotyping identified unknown ancestral consanguinity by detecting three autozygous regions. Because of the predominantly skeletal nature of the phenotype, the 389 genes localized to the autozygous intervals were prioritized for mutation analysis by correlation of their expression with known cartilage-selective genes via the UCLA Gene Expression Tool, UGET. The gene encoding the α1 chain of type XI collagen (COL11A1) was the only cartilage-selective gene among the three candidate intervals. Sequence analysis of COL11A1 in two genetically independent fibrochondrogenesis cases demonstrated that each was a compound heterozygote for a loss-of-function mutation on one allele and a mutation predicting substitution for a conserved triple-helical glycine residue on the other. The parents who were carriers of missense mutations had myopia. Early-onset hearing loss was noted in both parents who carried a loss-of-function allele, suggesting COL11A1 as a locus for mild, dominantly inherited hearing loss. These findings identify COL11A1 as a locus for fibrochondrogenesis and indicate that there might be phenotypic manifestations among carriers.