The type II collagenopathies: a spectrum of chondrodysplasias

ER procollagen storage defect without coupled unfolded protein response drives precocious arthritis

Collagenopathies are a group of clinically diverse disorders caused by defects in collagen folding and secretion. For example, mutations in the gene encoding collagen type-II, the primary collagen in cartilage, can lead to diverse chondrodysplasias. One example is the Gly1170Ser substitution in procollagen-II, which causes precocious osteoarthritis. Here, we biochemically and mechanistically characterize an induced pluripotent stem cell-based cartilage model of this disease, including both hetero- and homozygous genotypes. We show that Gly1170Ser procollagen-II is notably slow to fold and secrete. Instead, procollagen-II accumulates intracellularly, consistent with an endoplasmic reticulum (ER) storage disorder. Likely owing to the unique features of the collagen triple helix, this accumulation is not recognized by the unfolded protein response. Gly1170Ser procollagen-II interacts to a greater extent than wild-type with specific ER proteostasis network components, consistent with its slow folding. These findings provide mechanistic elucidation into the etiology of this disease. Moreover, the easily expandable cartilage model will enable rapid testing of therapeutic strategies to restore proteostasis in the collagenopathies.

ER procollagen storage defect without coupled unfolded protein response drives precocious arthritis

Collagenopathies are a group of clinically diverse disorders caused by defects in collagen folding and secretion. For example, mutations in the gene encoding collagen type-II, the primary collagen in cartilage, can lead to diverse chondrodysplasias. One example is the Gly1170Ser substitution in procollagen-II, which causes precocious osteoarthritis. Here, we biochemically and mechanistically characterize an induced pluripotent stem cell-based cartilage model of this disease, including both hetero- and homozygous genotypes. We show that Gly1170Ser procollagen-II is notably slow to fold and secrete. Instead, procollagen-II accumulates intracellularly, consistent with an endoplasmic reticulum (ER) storage disorder. Owing to unique features of the collagen triple helix, this accumulation is not recognized by the unfolded protein response. Gly1170Ser procollagen-II interacts to a greater extent than wild-type with specific proteostasis network components, consistent with its slow folding. These findings provide mechanistic elucidation into the etiology of this disease. Moreover, the cartilage model will enable rapid testing of therapeutic strategies to restore proteostasis in the collagenopathies.

Rgp1 contributes to craniofacial cartilage development and Rab8a-mediated collagen II secretion

Rgp1 was previously identified as a component of a guanine nucleotide exchange factor (GEF) complex to activate Rab6a-mediated trafficking events in and around the Golgi. While the role of Rgp1 in protein trafficking has been examined in vitro and in yeast, the role of Rgp1 during vertebrate embryogenesis and protein trafficking in vivo is unknown. Using genetic, CRISPR-induced zebrafish mutants for Rgp1 loss-of-function, we found that Rgp1 is required for craniofacial cartilage development. Within live rgp1-/- craniofacial chondrocytes, we observed altered movements of Rab6a+ vesicular compartments, consistent with a conserved mechanism described in vitro. Using transmission electron microscopy (TEM) and immunofluorescence analyses, we show that Rgp1 plays a role in the secretion of collagen II, the most abundant protein in cartilage. Our overexpression experiments revealed that Rab8a is a part of the post-Golgi collagen II trafficking pathway. Following loss of Rgp1, chondrocytes activate an Arf4b-mediated stress response and subsequently respond with nuclear DNA fragmentation and cell death. We propose that an Rgp1-regulated Rab6a-Rab8a pathway directs secretion of ECM cargoes such as collagen II, a pathway that may also be utilized in other tissues where coordinated trafficking and secretion of collagens and other large cargoes is required for normal development and tissue function.

Control of craniofacial development by the collagen receptor, discoidin domain receptor 2

Development of the craniofacial skeleton requires interactions between progenitor cells and the collagen-rich extracellular matrix (ECM). The mediators of these interactions are not well-defined. Mutations in the discoidin domain receptor 2 gene (DDR2), which encodes a non-integrin collagen receptor, are associated with human craniofacial abnormalities, such as midface hypoplasia and open fontanels. However, the exact role of this gene in craniofacial morphogenesis is not known. As will be shown, Ddr2-deficient mice exhibit defects in craniofacial bones including impaired calvarial growth and frontal suture formation, cranial base hypoplasia due to aberrant chondrogenesis and delayed ossification at growth plate synchondroses. These defects were associated with abnormal collagen fibril organization, chondrocyte proliferation and polarization. As established by localization and lineage-tracing studies, Ddr2 is expressed in progenitor cell-enriched craniofacial regions including sutures and synchondrosis resting zone cartilage, overlapping with GLI1 + cells, and contributing to chondrogenic and osteogenic lineages during skull growth. Tissue-specific knockouts further established the requirement for Ddr2 in GLI +skeletal progenitors and chondrocytes. These studies establish a cellular basis for regulation of craniofacial morphogenesis by this understudied collagen receptor and suggest that DDR2 is necessary for proper collagen organization, chondrocyte proliferation, and orientation.

A primer on skeletal dysplasias

Skeletal dysplasia encompasses a heterogeneous group of over 400 genetic disorders. They are individually rare, but collectively rather common with an approximate incidence of 1/5000. Thus, radiologists occasionally encounter skeletal dysplasias in their daily practices, and the topic is commonly brought up in radiology board examinations across the world. However, many radiologists and trainees struggle with this issue because of the lack of proper resources. The radiological diagnosis of skeletal dysplasias primarily rests on pattern recognition-a method that is often called the "Aunt Minnie" approach. Most skeletal dysplasias have an identifiable pattern of skeletal changes composed of unique findings and even pathognomonic findings. Thus, skeletal dysplasias are the best example to which the Aunt Minnie approach is readily applicable.

Congenital collagenopathies increased the risk of inguinal hernia developing and repair: analysis from a nationwide population-based cohort study

Herein, we aimed to explore whether male patients with congenital collagen diseases had a higher risk of inguinal herniation than patients without these diseases. Data were retrospectively collected from the National Health Insurance Research Database of Taiwan. The study cohort included 1,801 male patients diagnosed with congenital collagen diseases based on the ICD-9 CM diagnostic codes; after propensity score matching, the control group comprised 6,493 men without congenital collagen diseases. The primary endpoint was inguinal hernia repair during the observation period. During a median follow-up period of 133.9 months, the risk of inguinal herniation in the collagen group was significantly higher than that in the control group (HR = 2.237, 95% CI 1.646-3.291, p < 0.001). This phenomenon was observed in patients younger than 18 years (HR: 3.040, 95% CI 1.819-5.083, p < 0.001) and in those aged 18-80 years (HR: 1.909, 95% CI 1.186-3.073, p < 0.001). Asian men with congenital collagen diseases are at a high risk of developing inguinal hernias, regardless of age. Detailed physical examination and patient education should be performed for these patients to prevent inguinal herniation.

Somatic mutations in collagens are associated with a distinct tumor environment and overall survival in gastric cancer

BACKGROUND

Gastric cancer is a heterogeneous disease with poorly understood genetic and microenvironmental factors. Mutations in collagen genes are associated with genetic diseases that compromise tissue integrity, but their role in tumor progression has not been extensively reported. Aberrant collagen expression has been long associated with malignant tumor growth, invasion, chemoresistance, and patient outcomes. We hypothesized that somatic mutations in collagens could functionally alter the tumor extracellular matrix.

METHODS

We used publicly available datasets including The Tumor Cancer Genome Atlas (TCGA) to interrogate somatic mutations in collagens in stomach adenocarcinomas. To demonstrate that collagens were significantly mutated above background mutation rates, we used a moderated Kolmogorov-Smirnov test along with combination analysis with a bootstrap approach to define the background accounting for mutation rates. Association between mutations and clinicopathological features was evaluated by Fisher or chi-squared tests. Association with overall survival was assessed by Kaplan-Meier and the Cox-Proportional Hazards Model. Gene Set Enrichment Analysis was used to interrogate pathways. Immunohistochemistry and in situ hybridization tested expression of COL7A1 in stomach tumors.

RESULTS

In stomach adenocarcinomas, we identified individual collagen genes and sets of collagen genes harboring somatic mutations at a high frequency compared to background in both microsatellite stable, and microsatellite instable tumors in TCGA. Many of the missense mutations resemble the same types of loss of function mutations in collagenopathies that disrupt tissue formation and destabilize cells providing guidance to interpret the somatic mutations. We identified combinations of somatic mutations in collagens associated with overall survival, with a distinctive tumor microenvironment marked by lower matrisome expression and immune cell signatures. Truncation mutations were strongly associated with improved outcomes suggesting that loss of expression of secreted collagens impact tumor progression and treatment response. Germline collagenopathy variants guided interpretation of impactful somatic mutations on tumors.

CONCLUSIONS

These observations highlight that many collagens, expressed in non-physiologically relevant conditions in tumors, harbor impactful somatic mutations in tumors, suggesting new approaches for classification and therapy development in stomach cancer. In sum, these findings demonstrate how classification of tumors by collagen mutations identified strong links between specific genotypes and the tumor environment.

Clinical and Genetic Characteristics of COL2A1-Associated Skeletal Dysplasias in 60 Russian Patients: Part I

The significant variability in the clinical manifestations of COL2A1-associated skeletal dysplasias makes it necessary to conduct a clinical and genetic analysis of individual nosological variants, which will contribute to improving our understanding of the pathogenetic mechanisms and prognosis. We presented the clinical and genetic characteristics of 60 Russian pediatric patients with type II collagenopathies caused by previously described and newly identified variants in the COL2A1 gene. Diagnosis confirmation was carried out by new generation sequencing of the target panel with subsequent validation of the identified variants using automated Sanger sequencing. It has been shown that clinical forms of spondyloepiphyseal dysplasias predominate in childhood, both with more severe clinical manifestations (58%) and with unusual phenotypes of mild forms with normal growth (25%). However, Stickler syndrome, type I was less common (17%). In the COL2A1 gene, 28 novel variants were identified, and a total of 63% of the variants were found in the triple helix region resulted in glycine substitution in Gly-XY repeats, which were identified in patients with clinical manifestations of congenital spondyloepiphyseal dysplasia with varying severity, and were not found in Stickler syndrome, type I and Kniest dysplasia. In the C-propeptide region, five novel variants leading to the development of unusual phenotypes of spondyloepiphyseal dysplasia have been identified.

A novel homozygous variant of COL2A1 in a Chinese male with type II collagenopathy: a case report

BACKGROUND

Type II collagenopathies are a spectrum of diseases and skeletal dysplasia is one of the prominent features of collagenopathies. Molecular defects of the COL2A1 gene cause type II collagenopathies that is mainly an autosomal dominant disease, whereas some rare cases with autosomal recessive inheritance of mode have also been identified.

CASE PRESENTATION

The patient was a 5-year-old male with a short neck, flat face, epiphyseal dysplasia, irregular vertebral endplates, and osteochondritis. Sequencing result indicated NM_001844.4: c.3662C > T; p. (Ser1221Phe) a novel missense variant, leading to a serine-to-phenylalanine substitution. Sanger sequencing confirmed the variant compared to his parents and brother.

CONCLUSIONS

We identified a novel homozygous variant of the COL2A1 gene as the cause of type II collagenopathies in a Chinese male, enriching the spectrum of genotypes. This is the first case of type II collagenopathies inherited in an autosomal recessive manner in China and East Asia, and it is the first case that resulted from serine substitution in the world.

Germline Saturation Mutagenesis Induces Skeletal Phenotypes in Mice

Proper embryonic and postnatal skeletal development require coordination of myriad complex molecular mechanisms. Disruption of these processes, through genetic mutation, contributes to variation in skeletal development. We developed a high-throughput N-ethyl-N-nitrosourea (ENU)-induced saturation mutagenesis skeletal screening approach in mice to identify genes required for proper skeletal development. Here, we report initial results from live-animal X-ray and dual-energy X-ray absorptiometry (DXA) imaging of 27,607 G3 mice from 806 pedigrees, testing the effects of 32,198 coding/splicing mutations in 13,020 genes. A total of 39.7% of all autosomal genes were severely damaged or destroyed by mutations tested twice or more in the homozygous state. Results from our study demonstrate the feasibility of in vivo mutagenesis to identify mouse models of skeletal disease. Furthermore, our study demonstrates how ENU mutagenesis provides opportunities to create and characterize putative hypomorphic mutations in developmentally essential genes. Finally, we present a viable mouse model and case report of recessive skeletal disease caused by mutations in FAM20B. Results from this study, including engineered mouse models, are made publicly available via the online Mutagenetix database. © 2021 American Society for Bone and Mineral Research (ASBMR).

Combined exome sequencing and deep phenotyping in highly selected fetuses with skeletal dysplasia during the first and second trimesters improves diagnostic yield

OBJECTIVE

To investigate the genetic etiology of skeletal dysplasia in highly selected fetuses during the first and second trimesters using deep phenotyping and exome sequencing (ES).

METHOD

Fetuses with short femurs were identified using the established prenatal diagnostic approach. A multidisciplinary team reviewed fetal phenotypic information (prenatal ultrasound findings, fetal postmortem, and radiographs) in a cohort of highly selected fetuses with skeletal dysplasia during the first and second trimesters. The affected families underwent multiplatform genetic tests.

RESULTS

Of the 27 affected fetuses, 21 (77.8%) had pathogenic or potential pathogenic variations in the following genes: COL1A1, FGFR3, COL2A1, COL1A2, FLNB, DYNC2LI1, and TRIP11. Two fetuses had compound heterozygous mutations in DYNC2LI1 and TRIP11, respectively, and the other 19 carried de novo autosomal dominant variants. Novel variants were identified in COL1A1, COL2A1, COL1A2, DYNC2LI1, and TRIP11 in 11 fetuses. We also included the first description of the phenotype of odontochondrodysplasia in a prenatal setting.

CONCLUSIONS

ES or panel sequencing offers a high diagnostic yield for fetal skeletal dysplasia during the first and second trimesters. Comprehensive and complete phenotypic information is indispensable for genetic analysis and the expansion of genotype-phenotype correlations in fetal skeletal abnormalities.

A novel mutation of COL2A1 in a large Chinese family with avascular necrosis of the femoral head

Avascular necrosis of the femoral head (ANFH) is a debilitating bone disease, characterized by collapse of the femoral head and subsequent loss of hip joint function. Heterozygous mutations in COL2A1 have been identified to cause familial ANFH. Here we report on a large Chinese family with ANFH and a novel heterozygous mutation (c.3517 G > A, p.Gly1173Ser) in exon 50 of COL2A1 in the Gly-X-Y domain. Previously, only five different COL2A1 mutations have been described in patients with familial ANFH. Therefore, our findings provide significant clues to the phenotype-genotype relationships in familial ANFH and may be helpful in clinical diagnosis. Furthermore, these results should assist further studies of the mechanisms underlying collagen diseases.

Radiologic Features of Type II and Type XI Collagenopathies

Type II collagen is a major component of the cartilage matrix. Pathogenic variants (ie, disease-causing aberrations) in the type II collagen gene (COL2A1) lead to an abnormal structure of type II collagen, causing a large group of skeletal dysplasias termed type II collagenopathies. Because type II collagen is also located in the vitreous body of the eyes and inner ears, type II collagenopathies are commonly associated with vitreoretinal degeneration and hearing impairment. Type II collagenopathies can be radiologically divided into two major groups: the spondyloepiphyseal dysplasia congenita (SEDC) group and the Kniest-Stickler group. The SEDC group is characterized by delayed ossification of the juxtatruncal bones, including pear-shaped vertebrae. These collagenopathies comprise achondrogenesis type 2, hypochondrogenesis, SEDC, and other uncommon subtypes. The Kniest-Stickler group is characterized by disordered tubular bone growth that leads to "dumbbell" deformities. It comprises Kniest dysplasia and Stickler dysplasia type 1, whose radiographic manifestations overlap with those of type XI collagenopathies (a group of disorders due to abnormal type XI collagen) such as Stickler dysplasia types 2 and 3. This phenotypic overlap is caused by type II and type XI collagen molecules sharing part of the same connective tissues. The authors describe the diagnostic pathways to type II and type XI collagenopathies and the associated differential diagnoses. In addition, they review the clinical features and genetic bases of these conditions, which radiologists should know to participate in multidisciplinary care and translational research. Online supplemental material is available for this article. ^©RSNA, 2020.

Expanding the phenotype spectrum associated with pathogenic variants in the COL2A1 and COL11A1 genes

We report the clinical findings of 26 individuals from 16 unrelated families carrying variants in the COL2A1 or COL11A1 genes. Using Sanger and next-generation sequencing, 11 different COL2A1 variants (seven novel), were identified in 13 families (19 affected individuals), all diagnosed with Stickler syndrome (STL) type 1. In nine families, the COL2A1 disease-causing variant arose de novo. Phenotypically, we observed myopia (95%) and retinal detachment (47%), joint hyperflexibility (92%), midface retrusion (84%), cleft palate (53%), and various degrees of hearing impairment (50%). One patient had a splenic artery aneurysm. One affected individual carrying pathogenic variant in COL2A1 showed no ocular signs including no evidence of membranous vitreous anomaly. In three families (seven affected individuals), three novel COL11A1 variants were found. The propositus with a de novo variant showed an ultrarare Marshall/STL overlap. In the second family, the only common clinical sign was postlingual progressive sensorineural hearing impairment (DFNA37). Affected individuals from the third family had typical STL2 signs. The spectrum of disease phenotypes associated with COL2A1 or COL11A1 variants continues to expand and includes typical STL and various bone dysplasias, but also nonsyndromic hearing impairment, isolated myopia with or without retinal detachment, and STL phenotype without clinically detectable ocular pathology.

COL2A1 Gene Mutations: Mechanisms of Spondyloepiphyseal Dysplasia Congenita

The COL2A1 gene consists of 54 exons spanning over 31.5 kb and encodes for type II collagen. Type II collagen is the main component of hyaline cartilage extracellular matrix, nucleus pulposus of intervertebral discus, vitreous humor of the eye and inner ear structure. Molecular defects in COL2A1 gene cause a wide variety of rare autosomal-dominant conditions known as type II collagenopathies. A clear genotype-phenotype relationship is not yet known. However, some correlations are described. Spondyloephyseal dysplasia congenita was suggested for a short-trunk dwarfing condition affecting primarily the vertebrae and the proximal epiphyses of the long bones.

Diagnosis of Prenatal-Onset Achondrogenesis Type II by a Multidisciplinary Assessment: A Retrospective Study of 2 Cases

Aim

Achondrogenesis type II is a rare, lethal osteochondrodysplasia with considerable phenotypic heterogeneity. We describe our experience in diagnosing prenatal-onset achondrogenesis type II by a multidisciplinary assessment.

Methods

Two cases of fetal achondrogenesis type II were analyzed retrospectively using prenatal ultrasound evaluation, postnatal radiographic diagnosis, and molecular genetic testing of COL2A1.

Results

A causative mutation in the COL2A1 gene was found in both patients. Combined with postnatal radiographic examination, the final diagnosis of achondrogenesis type II was made.

Conclusion

Our findings emphasize the importance of a multidisciplinary assessment for the definitive diagnosis of achondrogenesis type II, which is paramount for proper genetic counseling.

Cartilage diseases

Hyaline cartilages, fibrocartilages and elastic cartilages play multiple roles in the human body including bearing loads in articular joints and intervertebral discs, providing joint lubrication, forming the external ears and nose, supporting the trachea, and forming the long bones during development and growth. The structure and organization of cartilage's extracellular matrix (ECM) are the primary determinants of normal function. Most diseases involving cartilage lead to dramatic changes in the ECM which can govern disease progression (e.g., in osteoarthritis), cause the main symptoms of the disease (e.g., dwarfism caused by genetically inherited mutations) or occur as collateral damage in pathological processes occurring in other nearby tissues (e.g., osteochondritis dissecans and inflammatory arthropathies). Challenges associated with cartilage diseases include poor understanding of the etiology and pathogenesis, delayed diagnoses due to the aneural nature of the tissue and drug delivery challenges due to the avascular nature of adult cartilages. This narrative review provides an overview of the clinical and pathological features as well as current treatment options available for various cartilage diseases. Late breaking advances are also described in the quest for development and delivery of effective disease modifying drugs for cartilage diseases including osteoarthritis, the most common form of arthritis that affects hundreds of millions of people worldwide.

Mandibular Distraction in a Patient With Type II Collagenopathy

Kniest dysplasia is an extremely rare form of type II collagenopathy associated with cleft palate, micrognathia, shortened trunk, arms and legs, and club foot. The authors present a case of an infant with this disorder who also had micrognathia and respiratory distress for which mandibular distraction was performed. Although abnormal collagen and impaired endochondral ossification is noted with Kniest dysplasia, adequate bone formation was observed across the distraction gap. Nonetheless, despite stable mandibular advancement, failure to consider concomitant restrictive lung disease resulted in tracheostomy dependence. The authors demonstrate that while successful bone regeneration can be achieved through distraction of intramembranous facial bones, discretion must still be employed in patients with collagenopathies.

Unsuccessful tracheal intubation in a patient with Kniest dysplasia undergoing repeated general anesthesia: a case report

Background

Kniest dysplasia is a type of chondrodysplasia characterized by severe craniofacial abnormalities including tracheomalacia, midface hypoplasia, and cleft palate.

Case presentation

We previously described a 6-year-old girl with Kniest dysplasia, in whom glottic edema rapidly developed after tracheal intubation. At the age of 13 years, a reoperation was scheduled to correct talipes equinovarus but was subsequently canceled due to failure of tracheal intubation and subsequent glottic edema. Airway evaluation by endoscopy and computed tomography 1 month later revealed severe laryngeal narrowing. Therefore, the second anesthesia was maintained with spinal anesthesia combined with sciatic nerve block without tracheal intubation.

Conclusion

Careful perioperative airway evaluation is required in patients with Kniest dysplasia, and alternative strategies for airway management other than tracheal intubation should be considered.

COL2A1 mutation (c.3508G>A) leads to avascular necrosis of the femoral head in a Chinese family: A case report

Avascular necrosis of the femoral head (ANFH) is a consequence of ischemia. Although the majority of cases of ANFH are sporadic, certain familial cases of ANFH have been reported to be associated with collagen type II α1 chain (COL2A1) mutations, which lead to COL2A1 gene dysfunction. The structure of secreted type II collagen contains a core area with a triple helical glycine (Gly)-X-Y domain, and the replacement of Gly in this region as a result of COL2A1 mutations may damage the structure of type II collagen. In the present study, a Chinese family with ANFH was recruited and genetic analysis was conducted to determine whether COL2A1 mutations were implicated in this familial ANFH. A three-generation family containing 31 members, as well as 20 patients with sporadic ANFH, were recruited for investigation. The diagnosis was performed by independent surgeons and radiologists according to internationally recognized criteria. In the present study, a heterozygous c.3508G>A mutation in exon 50 of the COL2A1 gene was identified, which results in the substitution of Gly with serine at codon 1,170. Furthermore, genetic pedigree analysis indicated that this mutation was inherited in an autosomal dominant manner. The present study revealed that a heterozygous c.3508G>A mutation in the COL2A1 gene was involved in ANFH development in one Chinese family. Therefore, it is proposed that individuals who carry this c.3508G>A mutation in the COL2A1 gene should receive genetic counseling and early intervention for ANFH.

Double non-contiguous fractures in a patient with spondylo-epiphyseal dysplasia with spinal ankylosis treated with open and percutaneous spinal fixation technique: a case report

Background

Patients with ankylosing spines are susceptible to developing spinal fractures even with minor trauma and can develop early or late neurological injuries. These fractures require early and aggressive surgical management to enable spinal stability and/or neural decompression. Being highly unstable by nature, they require relatively long segment instrumentation and fusion, which can increase paravertebral soft tissue damage and perioperative bleeding. The purpose of this report is to describe a rare case of traumatic double fractures at the cervico-thoracic and thoraco-lumbar transition zones in ankylosing spine with spondylo-epiphyseal dysplasia (SED) of unknown cause, which were successfully treated with a combined open and percutaneous spinal fusion procedure.

Case presentation

A 46-year-old woman who was diagnosed with non-contiguous fractures in cervico-thoracic and thoraco-lumbar junction zones among multiple injuries sustained in a traffic accident was treated with hybrid techniques for posterior instrumentation with an open approach using a computed tomography (CT)-based navigation system and percutaneous pedicle-screwing method. She regained mobility to pre-admission levels and started walking on crutches 3 months postoperatively. Genetic testing for the cause of SED revealed no mutation in the COL2A1 or TRPVR4 genes. The union of fractured spine was confirmed on CT scan 1 year postoperatively.

Conclusion

This is the first report of double spinal fractures in an ankylosing spine with genetically undetermined spondyloepiphyseal dysplasia. A long-segment posterior instrumentation procedure incorporating the invasive treatment of spinal fractures in ankylosing spondylitis or diffuse idiopathic hyperostosis was effective.

Recurrent c.G1636A (p.G546S) mutation of COL2A1 in a Chinese family with skeletal dysplasia and different metaphyseal changes: a case report

Background

Mutations in the COL2A1 gene cause type II collagenopathies characterized by skeletal dysplasia with a wide spectrum of phenotypic severity. Most COL2A1 mutations located in the triple-helical region, and the glycine to bulky amino acid substitutions (e.g., glycine to serine) in the Gly-X-Y repeat were identified frequently. However, the same COL2A1 mutations are associated with different phenotypes and the genotype-phenotype relationship is still poorly understood. Therefore, the studies of more patients about the recurrent mutations in COL2A1 will be needed for further research to provide more comprehensive clinical and genetic data. In this paper, we report a rare recurrent c.G1636A (p.G546S) mutation in COL2A1 associated with different metaphyseal changes in a Chinese family.

Case presentation

The proband (III-3) was the second child of the family with skeletal dysplasia. She was 2 years and 3 months old with disproportional short stature, short neck, pectus carinatum, genu varum, bilateral pes planus, and obvious waddling gait. Notably, she displayed severe metaphyseal lesions, especially typical “dappling” and “corner fracture” appearance, whereas no particular metaphyseal involvement was detected in the proband’s mother (II-3) and elder sister (III-2) in the family. We identified a heterozygous mutation (c.1636G > A) in COL2A1 in the three patients, causing the substitution of glycine to serine in codon 546. Although the same mutation has been reported in two previous studies, the phenotypes of the previous patients were different from those of our patients, and the characteristic “dappling” and “corner fracture” metaphyseal abnormalities were not reported previously.

Conclusions

In this study, we identified a c.G1636A (p.G546S) mutation in the COL2A1 associated with different metaphyseal changes, which was never reported in the literature. Our findings revealed a different causative amino acid substitution (glycine to serine) associated with the “dappling” and “corner fracture” metaphyseal abnormalities, and may provide a useful reference for evaluating the phenotypic spectrum and variability of type II collagenopathies.

Loss of DDRGK1 modulates SOX9 ubiquitination in spondyloepimetaphyseal dysplasia

Shohat-type spondyloepimetaphyseal dysplasia (SEMD) is a skeletal dysplasia that affects cartilage development. Similar skeletal disorders, such as spondyloepiphyseal dysplasias, are linked to mutations in type II collagen (COL2A1), but the causative gene in SEMD is not known. Here, we have performed whole-exome sequencing to identify a recurrent homozygous c.408+1G>A donor splice site loss-of-function mutation in DDRGK domain containing 1 (DDRGK1) in 4 families affected by SEMD. In zebrafish, ddrgk1 deficiency disrupted craniofacial cartilage development and led to decreased levels of the chondrogenic master transcription factor sox9 and its downstream target, col2a1. Overexpression of sox9 rescued the zebrafish chondrogenic and craniofacial phenotype generated by ddrgk1 knockdown, thus identifying DDRGK1 as a regulator of SOX9. Consistent with these results, Ddrgk1-/- mice displayed delayed limb bud chondrogenic condensation, decreased SOX9 protein expression and Col2a1 transcript levels, and increased apoptosis. Furthermore, we determined that DDRGK1 can directly bind to SOX9 to inhibit its ubiquitination and proteasomal degradation. Taken together, these data indicate that loss of DDRGK1 decreases SOX9 expression and causes a human skeletal dysplasia, identifying a mechanism that regulates chondrogenesis via modulation of SOX9 ubiquitination.

A novel type II collagen gene mutation in a family with spondyloepiphyseal dysplasia and extensive intrafamilial phenotypic diversity

The purpose of this study was to describe a family with spondyloepiphyseal dysplasia caused by a novel type II collagen gene (COL2A1) mutation and the family's phenotypic diversity. Clinical and radiographic examinations of skeletal dysplasia were conducted on seven affected family members across two generations. The entire coding region of COL2A1, including the flanking intron regions, was analyzed with PCR and direct sequencing. The stature of the subjects ranged from extremely short to within normal height range. Hip deformity and advanced osteoarthritis were noted in all the subjects, ranging from severe coxa plana to mild acetabular dysplasia. Atlantoaxial subluxation combined with a hypoplastic odontoid process was found in three of the subjects. Various degrees of platyspondyly were confirmed in all subjects. Genetically, a novel COL2A1 mutation (c.1349G>C, p.Gly450Ala) was identified in all the affected family members; however, it was not present in the one unaffected family member tested. We described a family with spondyloepiphyseal dysplasia and a novel COL2A1 mutation (c.1349G>C, p.Gly450Ala). Phenotypes were diverse even among individuals with the same mutation and within the same family.

Development and characterization of a eukaryotic expression system for human type II procollagen

Background

Triple helical collagens are the most abundant structural protein in vertebrates and are widely used as biomaterials for a variety of applications including drug delivery and cellular and tissue engineering. In these applications, the mechanics of this hierarchically structured protein play a key role, as does its chemical composition. To facilitate investigation into how gene mutations of collagen lead to disease as well as the rational development of tunable mechanical and chemical properties of this full-length protein, production of recombinant expressed protein is required.

Results

Here, we present a human type II procollagen expression system that produces full-length procollagen utilizing a previously characterized human fibrosarcoma cell line for production. The system exploits a non-covalently linked fluorescence readout for gene expression to facilitate screening of cell lines. Biochemical and biophysical characterization of the secreted, purified protein are used to demonstrate the proper formation and function of the protein. Assays to demonstrate fidelity include proteolytic digestion, mass spectrometric sequence and posttranslational composition analysis, circular dichroism spectroscopy, single-molecule stretching with optical tweezers, atomic-force microscopy imaging of fibril assembly, and transmission electron microscopy imaging of self-assembled fibrils.

Conclusions

Using a mammalian expression system, we produced full-length recombinant human type II procollagen. The integrity of the collagen preparation was verified by various structural and degradation assays. This system provides a platform from which to explore new directions in collagen manipulation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12896-015-0228-7) contains supplementary material, which is available to authorized users.

Kniest Dysplasia: New Radiographic Features in the Skeleton

Objective

To describe skeletal findings in patients with Kniest dysplasia, focusing on osseous abnormalities that have not been characteristically associated with this disorder.

Materials and Methods

This was a retrospective study. The radiographs of four patients with known Kniest Dysplasia were evaluated by three musculoskeletal radiologists.

Results

Bilateral radial head dislocations and bilateral clubfeet were seen in our series. Other characteristic findings for this dysplasia were seen in all four patients.

Conclusions

Clubfeet and radial head dislocations may be associated with Kniest dysplasia. The presence of these osseous findings in the context of multiple skeletal abnormalities suggestive of a skeletal dysplasia should indicate the possibility of Kniest dysplasia and pathognomonic features for this entity should be sought.

Unique mutation portraits and frequent COL2A1 gene alteration in chondrosarcoma

Chondrosarcoma is the second most frequent malignant bone tumor. However, the etiological background of chondrosarcomagenesis remains largely unknown, along with details on molecular alterations and potential therapeutic targets. Massively parallel paired-end sequencing of whole genomes of 10 primary chondrosarcomas revealed that the process of accumulation of somatic mutations is homogeneous irrespective of the pathological subtype or the presence of IDH1 mutations, is unique among a range of cancer types, and shares significant commonalities with that of prostate cancer. Clusters of structural alterations localized within a single chromosome were observed in four cases. Combined with targeted resequencing of additional cartilaginous tumor cohorts, we identified somatic alterations of the COL2A1 gene, which encodes an essential extracellular matrix protein in chondroskeletal development, in 19.3% of chondrosarcoma and 31.7% of enchondroma cases. Epigenetic regulators (IDH1 and YEATS2) and an activin/BMP signal component (ACVR2A) were recurrently altered. Furthermore, a novel FN1-ACVR2A fusion transcript was observed in both chondrosarcoma and osteochondromatosis cases. With the characteristic accumulative process of somatic changes as a background, molecular defects in chondrogenesis and aberrant epigenetic control are primarily causative of both benign and malignant cartilaginous tumors.

The importance of conventional radiography in the mutational analysis of skeletal dysplasias (the TRPV4 mutational family)

The spondylo and spondylometaphyseal dysplasias (SMDs) are characterized by vertebral changes and metaphyseal abnormalities of the tubular bones, which produce a phenotypic spectrum of disorders from the mild autosomal-dominant brachyolmia to SMD Kozlowski to autosomal-dominant metatropic dysplasia. Investigations have recently drawn on the similar radiographic features of those conditions to define a new family of skeletal dysplasias caused by mutations in the transient receptor potential cation channel vanilloid 4 (TRPV4). This review demonstrates the significance of radiography in the discovery of a new bone dysplasia family due to mutations in a single gene.

Control of chondrocyte gene expression by actin dynamics: a novel role of cholesterol/Ror-alpha signalling in endochondral bone growth

Elucidating the signalling pathways that regulate chondrocyte differentiation, such as the actin cytoskeleton and Rho GTPases, during development is essential for understanding of pathological conditions of cartilage, such as chondrodysplasias and osteoarthritis. Manipulation of actin dynamics in tibia organ cultures isolated from E15.5 mice results in pronounced enhancement of endochondral bone growth and specific changes in growth plate architecture. Global changes in gene expression were examined of primary chondrocytes isolated from embryonic tibia, treated with the compounds cytochalasin D, jasplakinolide (actin modifiers) and the ROCK inhibitor Y27632. Cytochalasin D elicited the most pronounced response and induced many features of hypertrophic chondrocyte differentiation. Bioinformatics analyses of microarray data and expression validation by real-time PCR and immunohistochemistry resulted in the identification of the nuclear receptor retinoid related orphan receptor-α (Ror-α) as a novel putative regulator of chondrocyte hypertrophy. Expression of Ror-α target genes, (Lpl, fatty acid binding protein 4 [Fabp4], Cd36 and kruppel-like factor 5 [Klf15]) were induced during chondrocyte hypertrophy and by cytochalasin D and are cholesterol dependent. Stimulation of Ror-α by cholesterol results in increased bone growth and enlarged, rounded cells, a phenotype similar to chondrocyte hypertrophy and to the changes induced by cytochalasin D, while inhibition of cholesterol synthesis by lovastatin inhibits cytochalasin D induced bone growth. Additionally, we show that in a mouse model of cartilage specific (Col2-Cre) Rac1, inactivation results in increased Hif-1α (a regulator of Rora gene expression) and Ror-α⁺ cells within hypertrophic growth plates. We provide evidence that cholesterol signalling through increased Ror-α expression stimulates chondrocyte hypertrophy and partially mediates responses of cartilage to actin dynamics.

Identification of an evolutionarily conserved regulatory element of the zebrafish col2a1a gene

Zebrafish (Danio rerio) is an excellent model organism for the study of vertebrate development including skeletogenesis. Studies of mammalian cartilage formation were greatly advanced through the use of a cartilage specific regulatory element of the Collagen type II alpha 1 (Col2a1) gene. In an effort to isolate such an element in zebrafish, we compared the expression of two col2a1 homologues and found that expression of col2a1b, a previously uncharacterized zebrafish homologue, only partially overlaps with col2a1a. We focused our analysis on col2a1a, as it is expressed in both the stacked chondrocytes and the perichondrium. By comparing the genomic sequence surrounding the predicted transcriptional start site of col2a1a among several species of teleosts we identified a small highly conserved sequence (R2) located 1.7 kb upstream of the presumptive transcriptional initiation site. Interestingly, neither the sequence nor location of this element is conserved between teleost and mammalian Col2a1. We generated transient and stable transgenic lines with just the R2 element or the entire 1.7 kb fragment 5' of the transcriptional initiation site. The identified regulatory elements enable the tracking of cellular development in various tissues by driving robust reporter expression in craniofacial cartilage, ear, notochord, floor plate, hypochord and fins in a pattern similar to the expression of endogenous col2a1a. Using a reporter gene driven by the R2 regulatory element, we analyzed the morphogenesis of the notochord sheath cells as they withdraw from the stack of initially uniform cells and encase the inflating vacuolated notochord cells. Finally, we show that like endogenous col2a1a, craniofacial expression of these reporter constructs depends on Sox9a transcription factor activity. At the same time, notochord expression is maintained after Sox9a knockdown, suggesting that other factors can activate expression through the identified regulatory element in this tissue.

Prenatal manifestation and management of a mother and child affected by spondyloperipheral dysplasia with a C-propeptide mutation in COL2A1: case report

It is not unusual for patients with "rare" conditions, such as skeletal dysplasias, to remain undiagnosed until adulthood. In such cases, a pregnancy may unexpectedly reveal hidden problems and special needs. A 28 year old primigravida was referred to us at 17 weeks for counselling with an undiagnosed skeletal dysplasia with specific skeletal anomalies suggesting the collagen 2 disorder, spondyloperipheral dysplasia (SPD; MIM 156550).

She was counselled about the probability of dominant inheritance and was offered a prenatal diagnosis by sonography. US examination at 17, 18 and 20 weeks revealed fetal macrocephaly, a narrow thorax, and shortening and bowing of long bones. The parents elected to continue the pregnancy. At birth the baby showed severe respiratory distress for four weeks which then resolved. Mutation analysis of both mother and child revealed a hitherto undescribed heterozygous nonsense mutation in the C-propeptide coding region of COL2A1 confirming the diagnosis of SPD while reinforcing the genotype-phenotype correlations between C-propeptide COL2A1 mutations and the SPD-Torrance spectrum. This case demonstrates the importance of a correct diagnosis even in adulthood, enabling individuals affected by rare conditions to be made aware about recurrence and pregnancy-associated risks, and potential complications in the newborn.

A histological and ultrastructural study of femoral head cartilage in a new type II collagenopathy

A new type II collagenopathy, caused by the p.Gly1170Ser mutation of COL2A1, which presents as premature hip osteoarthritis (OA), avascular necrosis of the femoral head (ANFH) or Legg-Calvé-Perthes (LCP) disease, was recently found in several families with an inherited disease of the hip joint. In this study, femoral head cartilage was harvested for histological and ultrastructural examination to determine the pre-existing generalised abnormalities of the mutant cartilage. The histological results showed that the hierarchical structure of the mutant cartilage and the embedded chondrocytes were markedly abnormal. The expression and distribution of type II collagen was non-uniform in sections of the mutant cartilage. Ultrastructural examination showed obvious abnormal chondrocytes and disarrangement of collagen fibres in the mutant cartilage. Furthermore, the predicted stability of type II collagen dramatically decreased with the substitution of serine for glycine. Our study demonstrated that the p.Gly1170Ser mutation of COL2A1 caused significant structural alterations in articular cartilage, which are responsible for the new type II collagenopathy.

Stickler syndrome caused by COL2A1 mutations: genotype-phenotype correlation in a series of 100 patients

Stickler syndrome is an autosomal dominant connective tissue disorder caused by mutations in different collagen genes. The aim of our study was to define more precisely the phenotype and genotype of Stickler syndrome type 1 by investigating a large series of patients with a heterozygous mutation in COL2A1. In 188 probands with the clinical diagnosis of Stickler syndrome, the COL2A1 gene was analyzed by either a mutation scanning technique or bidirectional fluorescent DNA sequencing. The effect of splice site alterations was investigated by analyzing mRNA. Multiplex ligation-dependent amplification analysis was used for the detection of intragenic deletions. We identified 77 different COL2A1 mutations in 100 affected individuals. Analysis of the splice site mutations showed unusual RNA isoforms, most of which contained a premature stop codon. Vitreous anomalies and retinal detachments were found more frequently in patients with a COL2A1 mutation compared with the mutation-negative group (P<0.01). Overall, 20 of 23 sporadic patients with a COL2A1 mutation had either a cleft palate or retinal detachment with vitreous anomalies. The presence of vitreous anomalies, retinal tears or detachments, cleft palate and a positive family history were shown to be good indicators for a COL2A1 defect. In conclusion, we confirm that Stickler syndrome type 1 is predominantly caused by loss-of-function mutations in the COL2A1 gene as >90% of the mutations were predicted to result in nonsense-mediated decay. On the basis of binary regression analysis, we developed a scoring system that may be useful when evaluating patients with Stickler syndrome.

Significant ocular findings are a feature of heritable bone dysplasias resulting from defects in type II collagen

BACKGROUND/AIMS

The type II collagenopathies are a phenotypically diverse group of genetic skeletal disorders caused by a mutation in the gene coding for type II collagen. Reports published before the causative mutations were discovered suggest heritable bone dysplasias with skeletal malformations may be associated with a vitreoretinopathy.

METHODS

A retrospective notes search of patients with a molecularly characterised type II collagenopathy chondrodysplasia who had been examined in the ophthalmology clinic was conducted.

RESULTS

13 of 14 patients had a highly abnormal vitreous appearance. One patient aged 11 presented with a total retinal detachment. Two other children aged 2 and 4 had bilateral flat multiple retinal tears on presentation. 10 of 12 patients refracted were myopic. Two patients had asymptomatic lens opacities: one associated with bilateral inferiorly subluxed lenses and the other with a zonule and lens coloboma.

CONCLUSION

Heritable skeletal disorders resulting from a mutation in the gene coding for type II collagen are associated with abnormal vitreous, myopia and peripheral cataract with lens subluxation. In bone dysplasias resulting from a defect of type II collagen there is likely to be a high risk of retinal detachment with a propensity to retinal tears at a young age.

The phenotypic spectrum in patients with arginine to cysteine mutations in the COL2A1 gene

BACKGROUND

The majority of COL2A1 missense mutations are substitutions of obligatory glycine residues in the triple helical domain. Only a few non-glycine missense mutations have been reported and among these, the arginine to cysteine substitutions predominate.

OBJECTIVE

To investigate in more detail the phenotype resulting from arginine to cysteine mutations in the COL2A1 gene.

METHODS

The clinical and radiographic phenotype of all patients in whom an arginine to cysteine mutation in the COL2A1 gene was identified in our laboratory, was studied and correlated with the abnormal genotype. The COL2A1 genotyping involved DHPLC analysis with subsequent sequencing of the abnormal fragments.

RESULTS

Six different mutations (R75C, R365C, R519C, R704C, R789C, R1076C) were found in 11 unrelated probands. Each mutation resulted in a rather constant and site-specific phenotype, but a perinatally lethal disorder was never observed. Spondyloarthropathy with normal stature and no ocular involvement were features of patients with the R75C, R519C, or R1076C mutation. Short third and/or fourth toes was a distinguishing feature of the R75C mutation and brachydactyly with enlarged finger joints a key feature of the R1076C substitution. Stickler dysplasia with brachydactyly was observed in patients with the R704C mutation. The R365C and R789C mutations resulted in classic Stickler dysplasia and spondyloepiphyseal dysplasia congenita (SEDC), respectively.

CONCLUSIONS

Arginine to cysteine mutations are rather infrequent COL2A1 mutations which cause a spectrum of phenotypes including classic SEDC and Stickler dysplasia, but also some unusual entities that have not yet been recognised and described as type II collagenopathies.

The p63 gene in EEC and other syndromes

Several autosomal dominantly inherited human syndromes have recently been shown to result from mutations in the p63 gene. These syndromes have various combinations of limb malformations fitting the split hand-split foot spectrum, orofacial clefting, and ectodermal dysplasia. The p63 syndrome family includes the EEC syndrome, AEC syndrome, ADULT syndrome, limb-mammary syndrome, and non-syndromic split hand/foot malformation. The pattern of heterozygous mutations is distinct for each of these syndromes. The functional effects on the p63 proteins also vary between syndromes. In all of these syndromes, the mutation appears to have both dominant negative and gain of function effects rather than causing a simple loss of function.

Report of five novel and one recurrent COL2A1 mutations with analysis of genotype-phenotype correlation in patients with a lethal type II collagen disorder

Achondrogenesis II-hypochondrogenesis and severe spondyloepiphyseal dysplasia congenita (SEDC) are lethal forms of dwarfism caused by dominant mutations in the type II collagen gene (COL2A1). To identify the underlying defect in seven cases with this group of conditions, we used the combined strategy of cartilage protein analysis and COL2A1 mutation analysis. Overmodified type II collagen and the presence of type I collagen was found in the cartilage matrix of all seven cases. Five patients were heterozygous for a nucleotide change that predicted a glycine substitution in the triple helical domain (G313S, G517V, G571A, G910C, G943S). In all five cases, analysis of cartilage type II collagen suggested incorporation of the abnormal alpha1(II) chain in the extracellular collagen trimers. The G943S mutation has been reported previously in another unrelated patient with a strikingly similar phenotype, illustrating the possible specific effect of the mutation. The radiographically less severely affected patient was heterozygous for a 4 bp deletion in the splice donor site of intron 35, likely to result in aberrant splicing. One case was shown to be heterozygous for a single nucleotide change predicted to result in a T1191N substitution in the carboxy-propeptide of the proalpha1(II) collagen chain. Study of the clinical, radiographic, and morphological features of the seven cases supports evidence for a phenotypic continuum between achondrogenesis II-hypochondrogenesis and lethal SEDC and suggests a relationship between the amount of type I collagen in the cartilage and the severity of the phenotype.

Autosomal recessive disorder otospondylomegaepiphyseal dysplasia is associated with loss-of-function mutations in the COL11A2 gene

Otospondylomegaepiphyseal dysplasia (OSMED) is an autosomal recessive skeletal dysplasia accompanied by severe hearing loss. The phenotype overlaps that of the autosomal dominant disorders-Stickler and Marshall syndromes-but can be distinguished by disproportionately short limbs, severe hearing loss, and lack of ocular involvement. In one family with OSMED, a homozygous Gly-->Arg substitution has been described in COL11A2, which codes for the alpha2 chain of type XI collagen. We report seven further families with OSMED. All affected individuals had a remarkably similar phenotype: profound sensorineural hearing loss, skeletal dysplasia with limb shortening and large epiphyses, cleft palate, an extremely flat face, hypoplasia of the mandible, a short nose with anteverted nares, and a flat nasal bridge. We screened affected individuals for mutations in COL11A2 and found different mutations in each family. Individuals from four families, including three with consanguineous parents, were homozygous for mutations. Individuals from three other families, in whom parents were nonconsanguineous, were compound heterozygous. Of the 10 identified mutations, 9 are predicted to cause premature termination of translation, and 1 is predicted to cause an in-frame deletion. We conclude that the OSMED phenotype is highly homogenous and results from homozygosity or compound heterozygosity for COL11A2 mutations, most of which are predicted to cause complete absence of alpha2(XI) chains.

Splicing mutations of 54-bp exons in the COL11A1 gene cause Marshall syndrome, but other mutations cause overlapping Marshall/Stickler phenotypes

Stickler and Marshall syndromes are dominantly inherited chondrodysplasias characterized by midfacial hypoplasia, high myopia, and sensorineural-hearing deficit. Since the characteristics of these syndromes overlap, it has been argued whether they are distinct entities or different manifestations of a single syndrome. Several mutations causing Stickler syndrome have been found in the COL2A1 gene, and one mutation causing Stickler syndrome and one causing Marshall syndrome have been detected in the COL11A1 gene. We characterize here the genomic structure of the COL11A1 gene. Screening of patients with Stickler, Stickler-like, or Marshall syndrome pointed to 23 novel mutations. Genotypic-phenotypic comparison revealed an association between the Marshall syndrome phenotype and splicing mutations of 54-bp exons in the C-terminal region of the COL11A1 gene. Null-allele mutations in the COL2A1 gene led to a typical phenotype of Stickler syndrome. Some patients, however, presented with phenotypes of both Marshall and Stickler syndromes.

Mutation of the type X collagen gene (COL10A1) causes spondylometaphyseal dysplasia

Spondylometaphyseal dysplasia (SMD) comprises a heterogeneous group of heritable skeletal dysplasias characterized by modifications of the vertebral bodies of the spine and metaphyses of the tubular bones. The genetic etiology of SMD is currently unknown; however, the type X collagen gene (COL10A1) is considered an excellent candidate, for two reasons: first, Schmid metaphyseal chondrodysplasia, a condition known to result from COL10A1 mutations, shows a significant phenotypic overlap with SMD; and, second, transgenic mice carrying deletions in type X collagen show SMD phenotypes. Hence, we examined the entire coding region of COL10A1 by direct sequencing of DNA from five unrelated patients with SMD and found a heterozygous missense mutation (Gly595Glu) cosegregating with the disease phenotype in one SMD family. This initial documented identification of a mutation in SMD expands our knowledge concerning the range of the pathological phenotypes that can be produced by aberrations of type X collagen (type X collagenopathy).

Marshall syndrome associated with a splicing defect at the COL11A1 locus

Marshall syndrome is a rare, autosomal dominant skeletal dysplasia that is phenotypically similar to the more common disorder Stickler syndrome. For a large kindred with Marshall syndrome, we demonstrate a splice-donor-site mutation in the COL11A1 gene that cosegregates with the phenotype. The G+1-->A transition causes in-frame skipping of a 54-bp exon and deletes amino acids 726-743 from the major triple-helical domain of the alpha1(XI) collagen polypeptide. The data support the hypothesis that the alpha1(XI) collagen polypeptide has an important role in skeletal morphogenesis that extends beyond its contribution to structural integrity of the cartilage extracellular matrix. Our results also demonstrate allelism of Marshall syndrome with the subset of Stickler syndrome families associated with COL11A1 mutations.

Progressive pseudorheumatoid dysplasia: report of a family and review

Progressive pseudorheumatoid dysplasia is an inherited skeletal dysplasia with radiographic changes notably in the spine, similar to spondyloepiphyseal dysplasia tarda. There is also articular cartilage involvement which gives it some clinical resemblance to rheumatoid arthritis. We report here on six subjects from one inbred family from Jordan. Based on previously published reports and this one, we review the clinical and radiological features and discuss the genetics and differential diagnosis of the disorder. We suggest the addition of the word "spondyloepiphyseal" to the name adopted by the International Working Group on Constitutional Diseases of Bone, to become "progressive pseudorheumatoid spondyloepiphyseal dysplasia". We also speculate on candidate genes for this disorder.

Achondrogenesis type 1B

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The deletion of six amino acids at the C-terminus of the alpha 1 (II) chain causes overmodification of type II and type XI collagen: further evidence for the association between small deletions in COL2A1 and Kniest dysplasia

We have identified an 18 bp deletion in exon 49 of the type II procollagen gene (COL2A1) in a patient with Kniest dysplasia. The deletion is located at the very C-terminus of the helical domain and removes two of three Gly-Pro-Pro triplets at positions 1007-1012, which are thought to be involved in helix formation and stability. Morphological investigation of an iliac crest biopsy showed large inclusions in the endoplasmic reticulum of chondrocytes, reflecting impaired secretion of type II collagen. Electrophoretic analysis of collagens extracted from cartilage or synthesised by cultured chondrocytes showed that type II and also type XI procollagen molecules containing mutant alpha 1 (II) chains showed post-translational overmodification. These observations provide further evidence for the general association of Kniest dysplasia with small deletions in the helical domain of type II collagen.