Age at onset-dependent presentations of premature hip osteoarthritis, avascular necrosis of the femoral head, or Legg-Calvé-Perthes disease in a single family, consequent upon a p.Gly1170Ser mutation of COL2A1

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.

Bone Remodeling and Bone Structural Genes in Legg-Calvé-Perthes Disease: The OPG rs2073618 and IL-6 rs1800795 Are Associated with High Risk in Mexican Patients

Legg-Calve-Perthes disease (LCPD) is an idiopathic avascular necrosis of the pediatric femoral head. Bone remodeling and bone structural genes have the potential to contribute to the progression of LCPD when there is disequilibrium between bone resorption and bone formation. A case-control study was performed to search for associations of several common polymorphisms in the genes Receptor Activator for Nuclear Factor κappa B (RANK), Receptor Activator for Nuclear Factor κappa B Ligand (RANKL), osteoprotegerin (OPG), interleukin (IL)-6, and type 1 collagen (COL1A1) with LCPD susceptibility in Mexican children. A total of 23 children with LCPD and 46 healthy controls were genotyped for seven polymorphisms (rs3018362, rs12585014, rs2073618, rs1800795, rs1800796, rs1800012, and rs2586498) in the RANK, RANKL, OPG, IL-6, and COL1A1 genes by real-time polymerase chain reaction with TaqMan probes. The variant allele (C) of IL-6 rs1800795 was associated with increased risk of LCPD (odds ratio [OR]: 3.8, 95% confidence interval [CI]: [1.08-13.54], p = 0.033), adjusting data by body mass index (BMI) and coagulation factor V (FV), the association with increased risk remained (OR: 4.9, 95% CI: [1.14-21.04], p = 0.025). The OPG polymorphism rs2073618, specifically GC-GG carriers, was associated with a more than fourfold increased risk of developing LCPD (OR: 4.34, 95% CI: [1.04-18.12], p = 0.033) when data were adjusted by BMI-FV. There was no significant association between RANK rs3018362, RANKL rs12585014, IL-6 rs1800796, COL1A1 rs1800012, and rs2586498 polymorphisms and LCPD in a sample of Mexican children. The rs1800975 and rs2037618 polymorphisms in the IL-6 and OPG genes, respectively, are informative markers of increased risk of LCPD in Mexican children.

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.

No correlation to collagen synthesis disorders in patients with Perthes' disease: a nationwide Swedish register study of 3488 patients

BACKGROUND

Mutations of the COL2A1 gene have been identified in patients with Perthes' disease. Several studies have hypothesised a connection between Perthes' disease and collagen synthesis disorders, especially COL2A1-related disorders, but no large studies on the subject have been made. The aim of this study was thus to discover if there is a connection between patients presenting with Perthes' disease, and collagen synthesis disorders. A secondary aim was to see if the children with both disorders had less optimal birth characteristics than the rest.

METHODS

Swedish national registers were used to collect data on children diagnosed with Perthes' disease or a collagen synthesis disorder. These registers include all births in Sweden, and data from both outpatient and in-hospital visits. A wide range of data is included besides diagnoses. All children with follow-up data to the age of 15 years were included. Pearson's chi-square was used for analysis. Statistical significance was further analysed with Fisher's Exact Test.

RESULTS

In total, 3488 children with either diagnosis were included. 1620 children had only Perthes disease, while 1808 children had only a collagen synthesis disorder. Five children were found to have both the diagnosis Perthes' disease and a collagen synthesis disorder. One child was large for their gestational age and none of the children had a low birthweight. Two of the children were moderately preterm.

CONCLUSIONS

The distinct lack of overlap in such a large body of material raises doubt about a connection between the presentation of Perthes' disease and collagen synthesis disorders, either COL2A1-related or not. We could not find an overrepresentation of less optimal birth characteristics either.

Legg-Calve-Perthes' disease: an opportunity to prevent blindness?

Legg-Calve-Perthes' disease (LCP) is defined as avascular necrosis of the femoral head in a child and may present to a variety of disciplines from general practice to orthopaedics, paediatrics, rheumatology and more. The Stickler syndromes are a group of disorders of type II, IX and XI collagen associated with hip dysplasia, retinal detachment, deafness and cleft palate. The pathogenesis of LCP disease remains an enigma but there have been a small number of cases reporting variants in the gene encoding the α1 chain of type II collagen (COL2A1). Variants in COL2A1 are known to cause type 1 Stickler syndrome (MIM 108300, 609508), which is a connective tissue disorder with a very high risk of childhood blindness, and it is also associated with dysplastic development of the femoral head. It is unclear whether COL2A1 variants make a definitive contribution to both disorders, or whether the two are indistinguishable using current clinical diagnostic techniques. In this paper, we compare the two conditions and present a case series of 19 patients with genetically confirmed type 1 Stickler syndrome presenting with a historic diagnosis of LCP. In contrast to isolated LCP, children with type 1 Stickler syndrome have a very high risk of blindness from giant retinal tear detachment, but this is now largely preventable if a timely diagnosis is made. This paper highlights the potential for avoidable blindness in children presenting to clinicians with features suggestive of LCP disease but with underlying Stickler syndrome and proposes a simple scoring system to assist clinicians.

Bone tissue engineering for treating osteonecrosis of the femoral head

Osteonecrosis of the femoral head (ONFH) is a devastating and complicated disease with an unclear etiology. Femoral head-preserving surgeries have been devoted to delaying and hindering the collapse of the femoral head since their introduction in the last century. However, the isolated femoral head-preserving surgeries cannot prevent the natural progression of ONFH, and the combination of autogenous or allogeneic bone grafting often leads to many undesired complications. To tackle this dilemma, bone tissue engineering has been widely developed to compensate for the deficiencies of these surgeries. During the last decades, great progress has been made in ingenious bone tissue engineering for ONFH treatment. Herein, we comprehensively summarize the state-of-the-art progress made in bone tissue engineering for ONFH treatment. The definition, classification, etiology, diagnosis, and current treatments of ONFH are first described. Then, the recent progress in the development of various bone-repairing biomaterials, including bioceramics, natural polymers, synthetic polymers, and metals, for treating ONFH is presented. Thereafter, regenerative therapies for ONFH treatment are also discussed. Finally, we give some personal insights on the current challenges of these therapeutic strategies in the clinic and the future development of bone tissue engineering for ONFH treatment.

Molecular Biomarkers in Perthes Disease: A Review

BACKGROUND

Perthes disease is a juvenile form of osteonecrosis of the femoral head that affects children under the age of 15. One hundred years after its discovery, some light has been shed on its etiology and the biological factors relevant to its etiology and disease severity.

METHODS

The aim of this study was to summarize the literature findings on the biological factors relevant to the pathogenesis of Perthes disease, their diagnostic and clinical significance, and their therapeutic potential. A special focus on candidate genes as susceptibility factors and factors relevant to clinical severity was made, where studies reporting clinical or preclinical results were considered as the inclusion criteria. PubMed databases were searched by two independent researchers. Sixty-eight articles were included in this review. Results on the factors relevant to vascular involvement and inflammatory molecules indicated as factors that contribute to impaired bone remodeling have been summarized. Moreover, several candidate genes relevant to an active phase of the disease have been suggested as possible biological therapeutic targets.

CONCLUSIONS

Delineation of molecular biomarkers that underlie the pathophysiological process of Perthes disease can allow for the provision of earlier and more accurate diagnoses of the disease and more precise follow-ups and treatment in the early phases of the disease.

Can large doses of glucocorticoids lead to Perthes? a case report and review of the literature

Background

Perthes disease (Legg-Calvé-Perthes, LCP) is a self-limited and non-systemic disease occurring in the femoral heads of children, which is mainly manifested as an ischemic necrosis of the femoral head epiphysis, leading to subchondral ossification injury of the femoral head.

Case presentation

Here we report a case of 11-year-old child with long-term use of high-dose glucocorticoids. With MRI examination finding the epiphyseal necrosis of right humeral head, femur and tibia, and X-ray examination finding bilateral femoral head necrosis, the child was diagnosed as Perthes disease based on his clinical and imaging data.

Conclusions

Long-term and high-dose glucocorticoids may be one of the causes of Perthes disease.

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.

Does early and aggressive management of significant extrusion of the femoral head affect the outcome of Perthes' disease with the age of onset younger than 7 years?

Background

Little literature exists regarding aggressive treatment of the extrusion in the early stage of the disease and the outcome at skeletal maturity. The purpose of the study was to evaluate the outcome of the disease with onset younger than 7 years, treated in the early stage of the disease, with aggressive management of significant extrusion (immediate containment with fixed abduction brace in children less than 5 years and varus derotation osteotomy in older children), and reached skeletal maturity.

Methods

All children with the age of onset younger than 7 years of disease during active Perthes disease were prospectively followed. Children with early stages of the disease (modified Elizabethtown classification) and reached skeletal maturity were included (68 children). The extrusion of the femur head was calculated by Reimer’s migration index on both sides. A migration difference 12 % or above was considered as “significant extrusion”. Children without significant extrusion were treated non-operatively; children with significant extrusion were treated with varus derotation osteotomy. The final radiological outcome was assessed by the Stulberg classification and sphericity deviation score (SDS). The independent “t” test and Chi-square test were done to compare the difference between the two groups.

Results

The mean age at the onset and the final follow-up was 5.7 years and 15.3 years. The frequency of significant extrusion was 57%. At the final follow-up, an excellent clinical outcome and radiological outcomes (in 88% hips) were noted. There was no significant difference in the Stulberg groups and SDS (sphericity deviation score) in both groups.

Conclusion

The outcome of the children who had the age of onset of the disease less than 7 years was good with early and aggressive management of the extrusion. The reversal of extrusion is associated with a similar result of non-operative children in this age group.

Level of evidence

III.

Japanese Orthopaedic Association 2019 Guidelines for osteonecrosis of the femoral head

PURPOSE

The Clinical Practice Guidelines for Osteonecrosis of the Femoral Head (ONFH) 2019 Edition, written by the working group for ONFH guidelines of the Japanese Investigation Committee (JIC) for ONFH under the auspices of the Japanese Ministry of Health, Labour, and Welfare and endorsed by the Japanese Orthopaedic Association, were published in Japanese in October 2019. The objective of this guideline is to provide a support tool for decision-making between doctors and patients.

METHODS

Procedures for developing this guideline were based on the Medical Information Network Distribution Service Handbook for Clinical Practice Guideline Development 2014, which proposed an appropriate method for preparing clinical guidelines in Japan.

RESULTS

This clinical practice guideline consists of 7 chapters: epidemiology; pathology; diagnosis; conservative therapy; surgical treatment: bone transplantation/cell therapy; surgical treatment: osteotomy; and surgical treatment: hip replacement. Twelve background questions and 13 clinical questions were determined to define the basic features of the disease and to be addressed when deciding treatment in daily practice, respectively.

CONCLUSIONS

The clinical practice guidelines for the ONFH 2019 edition will be useful for physicians, investigators, and medical staff in clinical practice, as well as for patients, during the decision-making process when defining how to treat ONFH.

Systems analysis of avascular necrosis of femoral head using integrative data analysis and literature mining delineates pathways associated with disease

Avascular necrosis of femoral head (AVNFH) is a debilitating disease, which affects the middle aged population. Though the disease is managed using bisphosphonate, it eventually leads to total hip replacement due to collapse of femoral head. Studies regarding the association of single nucleotide polymorphisms with AVNFH, transcriptomics, proteomics, metabolomics, biophysical, ultrastructural and histopathology have been carried out. Functional validation of SNPs was carried out using literature. An integrated systems analysis using the available datasets might help to gain further insights into the disease process. We have carried out an analysis of transcriptomic data from GEO-database, SNPs associated with AVNFH, proteomic and metabolomic data collected from literature. Based on deficiency of vitamins in AVNFH, an enzyme-cofactor network was generated. The datasets are analyzed using ClueGO and the genes are binned into pathways. Metabolomic datasets are analyzed using MetaboAnalyst. Centrality analysis using CytoNCA on the data sets showed cystathionine beta synthase and methylmalonyl-CoA-mutase to be common to 3 out of 4 datasets. Further, the genes common to at least two data sets were analyzed using DisGeNET, which showed their involvement with various diseases, most of which were risk factors associated with AVNFH. Our analysis shows elevated homocysteine, hypoxia, coagulation, Osteoclast differentiation and endochondral ossification as the major pathways associated with disease which correlated with histopathology, IHC, MRI, Micro-Raman spectroscopy etc. The analysis shows AVNFH to be a multi-systemic disease and provides molecular signatures that are characteristic to the disease process.

Integrated analysis of COL2A1 variant data and classification of type II collagenopathies

The COL2A1 gene encodes the alpha-1 chain of type II procollagen. Type II collagen, comprised of three identical alpha-1 chains, is the major component of cartilage. COL2A1 gene variants are the etiologies of genetic diseases, termed type II collagenopathies, with a wide spectrum of clinical presentations. To date, at least 460 distinct COL2A1 mutations, identified in 663 independent probands, and 21 definite disorders have been reported. Nevertheless, a well-defined genotype-phenotype correlation has not been established, and few hot spots of mutation have been reported. In this study, we analyzed data of COL2A1 variants and clinical information of patients obtained from the Leiden Open Variation Database 3.0, as well as the currently available relevant literature. We determined the characteristics of the COL2A1 variants and distributions of the clinical manifestations in patients, and identified four likely genotype-phenotype correlations. Moreover, we classified 21 COL2A1-related disorders into five categories, which may assist clinicians in understanding the essence of these complex phenotypes and prompt genetic screening in clinical practice.

Aetiology of Legg-Calvé-Perthes disease: A systematic review

BACKGROUND

Legg-Calvé-Perthes disease (LCPD) is a clinical condition affecting the femoral head of children during their growth. Its prevalence is set to be between 0.4/100000 to 29.0/100000 children less than 15 years of age with a peak of incidence in children aged from 4 years to 8 years. LCPD aetiology has been widely studied, but it is still poorly understood.

AIM

To analyse the available literature to document the up-to-date evidence on LCPD aetiology.

METHODS

A systematic review of the literature was performed regarding LCPD aetiology, using the following inclusion criteria: studies of any level of evidence, reporting clinical or preclinical results and dealing with the aetiology or pathogenesis of LCPD. Two reviewers searched the PubMed and Science Direct databases from their date of inception to the 20th of May 2018 in accordance with the Preferred Reporting Items for Systemic Reviews and Meta-Analyses guidelines. To achieve the maximum sensitivity of the search strategy, we combined the terms: ‘‘Perthes disease OR LCPD OR children avascular femoral head necrosis” with “pathology OR aetiology OR biomechanics OR genetics” as either key words or MeSH terms.

RESULTS

We include 64 articles in this review. The available evidence on LCPD aetiology is still debated. Several hypotheses have been researched, but none of them was found decisive. While emerging evidence showed the role of environmental risk factors and evidence from twin studies did not support a major role for genetic factors, a congenital or acquired predisposition cannot be excluded in disease pathogenesis. One of the most supported theories involved mechanical induced ischemia that evolved into avascular necrosis of the femoral head in sensible patients.

CONCLUSION

The literature available on the aetiology of LCPD presents major limitations in terms of great heterogeneity and a lack of high-profile studies. Although a lot of studies focused on the genetic, biomechanical and radiological background of the disease, there is a lack of consensus on one or multiple major actors of the etiopathogenesis. More studies are needed to understand the complex and multifactorial genesis of the avascular necrosis characterizing the disease.

Collagen type II suppresses articular chondrocyte hypertrophy and osteoarthritis progression by promoting integrin β1-SMAD1 interaction

Hypertrophic differentiation is not only the terminal process of endochondral ossification in the growth plate but is also an important pathological change in osteoarthritic cartilage. Collagen type II (COL2A1) was previously considered to be only a structural component of the cartilage matrix, but recently, it has been revealed to be an extracellular signaling molecule that can significantly suppress chondrocyte hypertrophy. However, the mechanisms by which COL2A1 regulates hypertrophic differentiation remain unclear. In our study, a Col2a1 p.Gly1170Ser mutant mouse model was constructed, and Col2a1 loss was demonstrated in homozygotes. Loss of Col2a1 was found to accelerate chondrocyte hypertrophy through the bone morphogenetic protein (BMP)-SMAD1 pathway. Upon interacting with COL2A1, integrin β1 (ITGB1), the major receptor for COL2A1, competed with BMP receptors for binding to SMAD1 and then inhibited SMAD1 activation and nuclear import. COL2A1 could also activate ITGB1-induced ERK1/2 phosphorylation and, through ERK1/2-SMAD1 interaction, it further repressed SMAD1 activation, thus inhibiting BMP-SMAD1-mediated chondrocyte hypertrophy. Moreover, COL2A1 expression was downregulated, while chondrocyte hypertrophic markers and BMP-SMAD1 signaling activity were upregulated in degenerative human articular cartilage. Our study reveals novel mechanisms for the inhibition of chondrocyte hypertrophy by COL2A1 and suggests that the degradation and decrease in COL2A1 might initiate and promote osteoarthritis progression.

A signaling feedback loop that contributes to cartilage degeneration may offer a fruitful target for the treatment of osteoarthritis. During the early stages of this disorder, cartilage-forming chondrocytes undergo a process of expansion known as hypertrophy, after which they die and are replaced by calcium. Researchers led by Peiqiang Su and Dongsheng Huang of Sun Yat-sen University have demonstrated that COL2A1, an important structural protein, represents an important safeguard against hypertrophy. COL2A1 helps maintain chondrocytes in their normal, healthy state, but Su and Huang showed that signaling factors produced during cartilage repair can reduce COL2A1 levels. This in turn accelerates hypertrophy, promoting further depletion of COL2A1 and ultimately leading to full-blown osteoarthritis. Drugs that break this cycle and preserve COL2A1 could thus help protect endangered joints before the damage becomes severe.

Exome sequencing reveals a novel COL2A1 mutation implicated in multiple epiphyseal dysplasia

Mutations in the COMP, COL9A1, COL9A2, COL9A3, MATN3, and SLC26A2 genes cause approximately 70% of multiple epiphyseal dysplasia (MED) cases. The genetic changes involved in the etiology of the remaining cases are still unknown, suggesting that other genes contribute to MED development. Our goal was to identify a mutation causing an autosomal dominant form of MED in a large multigenerational family. Initially, we excluded all genes known to be associated with autosomal dominant MED by using microsatellite and SNP markers. Follow-up with whole-exome sequencing analysis revealed a mutation c.2032G>A (p.Gly678Arg) in the COL2A1 gene (NCBI Reference Sequence: NM_001844.4), which co-segregated with the disease phenotype in this family, manifested by severe hip dysplasia and osteoarthritis. One of the affected family members had a double-layered patella, which is frequently seen in patients with autosomal recessive MED caused by DTDST mutations and sporadically in the dominant form of MED caused by COL9A2 defect.

IL6 receptor blockade preserves articular cartilage and increases bone volume following ischemic osteonecrosis in immature mice

OBJECTIVE

Juvenile ischemic osteonecrosis (JIO) of the femoral head is one of the most serious hip disorders causing a permanent deformity of the femoral head in childhood. We recently reported that interleukin 6 (IL6) is predominantly increased in the hip synovial fluid of patients with JIO and that articular chondrocytes are primary source of IL6. This study investigated whether an inhibition of IL6 receptor improves cartilage preservation and bone healing in JIO.

METHOD

A small animal model (i.e., 6-week-old mouse) of JIO was treated with either saline or tocilizumab, an IL6 receptor blocker, for 6 weeks.

RESULTS

TUNEL-positive chondrocytes in the articular cartilage were reduced by the tocilizumab treatment, concomitant with the increase in cartilage matrix. The levels of a cartilage anabolic marker Sox9 was significantly increased in the articular cartilage of mice treated with tocilizumab. Micro-CT assessment showed tocilizumab treatment significantly increased trabecular epiphyseal bone volume (P = 0.001, n = 10), thickness (P = 0.007) and number (P = 0.014) and decreased bone separation (P = 0.002) and its deformity (P = 0.003). A bone formation marker, BMP2, and an angiogenic marker, vascular endothelial growth factor (VEGF), were both significantly increased by tocilizumab treatment under hypoxia using human chondrocytes while the bone resorption marker, RANKL/OPG ratio, was reduced.

CONCLUSION

Tocilizumab treatment following ischemic osteonecrosis has cartilage anabolic effect and increases bone volume in JIO mouse model. The findings lead to a possible application of tocilizumab for preclinical study using a large animal model of JIO and a clinical trial to validate this treatment.

Studying the effects of haplotype partitioning methods on the RA-associated genomic results from the North American Rheumatoid Arthritis Consortium (NARAC) dataset

•

Haplotype blocks methods plays a complementary role to the single-SNP approaches.

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CIT, FGT, SSLD, and single-SNP methods should be applied to discover the markers.

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Selection of the method used for the association has an impact on the biomarkers.

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SSLD method detected more significant SNPs than CIT, FGT, and single-SNP methods.

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The 383 SNPs discovered by all methods are significantly associated with RA.

The human genome, which includes thousands of genes, represents a big data challenge. Rheumatoid arthritis (RA) is a complex autoimmune disease with a genetic basis. Many single-nucleotide polymorphism (SNP) association methods partition a genome into haplotype blocks. The aim of this genome wide association study (GWAS) was to select the most appropriate haplotype block partitioning method for the North American Rheumatoid Arthritis Consortium (NARAC) dataset. The methods used for the NARAC dataset were the individual SNP approach and the following haplotype block methods: the four-gamete test (FGT), confidence interval test (CIT), and solid spine of linkage disequilibrium (SSLD). The measured parameters that reflect the strength of the association between the biomarker and RA were the P-value after Bonferroni correction and other parameters used to compare the output of each haplotype block method. This work presents a comparison among the individual SNP approach and the three haplotype block methods to select the method that can detect all the significant SNPs when applied alone. The GWAS results from the NARAC dataset obtained with the different methods are presented. The individual SNP, CIT, FGT, and SSLD methods detected 541, 1516, 1551, and 1831 RA-associated SNPs respectively, and the individual SNP, FGT, CIT, and SSLD methods detected 65, 156, 159, and 450 significant SNPs respectively, that were not detected by the other methods. Three hundred eighty-three SNPs were discovered by the haplotype block methods and the individual SNP approach, while 1021 SNPs were discovered by all three haplotype block methods. The 383 SNPs detected by all the methods are promising candidates for studying RA susceptibility. A hybrid technique involving all four methods should be applied to detect the significant SNPs associated with RA in the NARAC dataset, but the SSLD method may be preferred because of its advantages when only one method was used.

Osteonecrosis of the femoral head: genetic basis

PURPOSE

Genetic factors and hereditary forms of osteonecrosis of the femoral head (ONFH) have been elucidated through genetic association studies. The significance of these cases is that they suggest an alternative hypothesis to the development of the disease. This review presents a summary of single nucleotide polymorphisms (SNPs) and other genetic mutation variations found in association with ONFH, including our recent identification of a novel mutation in the transient receptor potential vanilloid 4 (TRPV4) gene in association with inherited ONFH. The purpose of this review is to consolidate and categorize genetic linkages according to physiological pathways.

METHODS

A systematic review of literature from PubMed and Google Scholar was undertaken with a focus on genetic linkages and hereditary case studies of the disease. Recent genetic analysis studies published after 2007 were the focus of genetic linkages in non-hereditary cases.

RESULTS

The summary of these genetic findings identifies biological processes believed to be involved in the development of ONFH, which include circulation, steroid metabolism, immunity, and the regulation of bone formation.

CONCLUSION

Taken together, these associations may lead to new pathways of bone repair and remodeling while opening new avenues for therapeutic targets. Knowledge of genetic variations could help identify individuals considered to be at higher risk of developing ONFH and prevent the multiple hit effect.

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.

Is Legg-Calvé-Perthes Disease a Local Manifestation of a Systemic Condition?

BACKGROUND

Osteochondrosis includes numerous diseases that occur during rapid growth, characterized by disturbances of endochondral ossification. One example, Legg-Calvé-Perthes disease, is characterized by disruption of the blood supply to the femoral head epiphysis, and a systemic etiology often has been suggested. If this were the case, secondary osteochondroses at locations other than the hip might be expected to be more common among patients with Legg-Calvé-Perthes disease, but to our knowledge, this has not been evaluated in a nationwide sample.

QUESTIONS/PURPOSES

(1) Do patients with Legg-Calvé-Perthes disease have an increased prevalence of secondary osteochondroses at locations other than the hip? (2) Is the concept of Legg-Calvé-Perthes disease a systemic etiology supported by a higher prevalence of the metabolic diseases obesity and hypothyroidism?

METHODS

We designed a retrospective population-based cohort study with data derived from the Swedish Patient Registry (SPR). The SPR was established in 1964 and collects information on dates of hospital admission and discharge, registered diagnoses (categorized along the International Classification of Diseases [ICD]), and applied treatments during the entire lifetime of all Swedish citizens with high validity. Analyzing the time span from 1964 to 2011, we identified 3183 patients with an ICD code indicative of Legg-Calvé-Perthes disease and additionally sampled 10 control individuals per patient with Legg-Calvé-Perthes disease, matching for sex, age, and residence, resulting in 31,817 control individuals. The prevalence of secondary osteochondroses, obesity, and hypothyroidism was calculated separately for patients with Legg-Calvé-Perthes disease and control individuals based on the presence of ICD codes indicative of these conditions. Using logistic regression analysis, we compared the adjusted relative risk of having either of these conditions develop between patients with Legg-Calvé-Perthes disease and their matched control subjects. The mean followup was 26.1 years (range, 2.8-65 years).

RESULTS

The prevalence of secondary osteochondroses was greater among patients with Legg-Calvé-Perthes disease (3.11%) than among control subjects (0.31%), resulting in an increased adjusted risk of an association with such lesions in the patients (relative risk [RR], 10.3; 95% confidence interval [CI], 7.7-13.6; p < 0.001). When stratified by sex, we attained a similarly increased risk ratio for females (RR, 12.5; 95% CI, 6.1-25.8; p < 0.001) as for males (RR, 9.9; 95% CI, 7.3-13.5; p < 0.001). Patients with Legg-Calvé-Perthes disease had an increased adjusted risk of an association with obesity (RR, 2.8; 95% CI, 1.9-4.0; p < 0.001) or hypothyroidism (RR, 2.6; 95% CI, 1.7-3.8; p < 0.001) when compared with control subjects.

CONCLUSIONS

To our knowledge, this is the first population-based description of a robust association of Legg-Calvé-Perthes disease with osteochondroses at locations other than the hip, and we also found increased risk estimates for an association with obesity and hypothyroidism in patients with Legg-Calvé-Perthes disease. Our findings strengthen the hypothesis that Legg-Calvé-Perthes disease is the local manifestation of a systemic disease, indicative of an underlying common disease pathway that requires further investigation. Physicians should be aware that patients with Legg-Calvé-Perthes disease may present with secondary osteochondroses and metabolic comorbidities.

LEVEL OF EVIDENCE

Level III, prognostic study.

Stickler syndrome in children: a radiological review

AIM

To review the radiological findings of the largest cohort to date of paediatric patients with Stickler syndrome, all with confirmed molecular genetic analysis and sub-typing.

PATIENTS AND METHODS

It is understood that the National Health Service (NHS) commissioned service at Addenbrookes Hospital, Cambridge, UK has the largest cohort of Stickler syndrome patients in the paediatric age group worldwide with 240 registered children. Fifty-nine were assessed radiologically and for their genotypes. These radiographs were reviewed and 74 knee, 45 pelvic, and 47 spinal examinations were evaluated.

RESULTS

Radiological features were noted in 45.9% of knee radiographs, 11.1% of pelvic radiographs, and 42.6% of spinal radiographs. The findings were reviewed in the light of each patient's specific genetic Stickler syndrome subtype.

CONCLUSION

The prevalence of orthopaedic abnormalities overall in the present series is substantially below those published in previous smaller case series. This would support the more recent findings of an array of ocular only phenotypes of Stickler syndrome described in the literature.

11β-hydroxysteroid dehydrogenases as targets in the treatment of steroid-associated femoral head necrosis using antler extract

The aim of the present study was to investigate the therapeutic effect of deer antler extract on avascular necrosis of the femoral head (ANFH) induced by steroids, and to confirm that 11β-hydroxysteroid dehydrogenases (11β-HSD) are one of the targets of treatment with antler extract. A total of 30 rabbits were randomly divided into 5 groups (n=6): A control, ANFH, ANFH + antler (250 mg/kg), ANFH + antler (500 mg/kg) and ANFH + antler (1,000 mg/kg) group. Rabbits in the experimental groups were injected with methylprednisolone and horse serum to establish a steroid-induced ANFH (SANFH) model. Rabbits in the ANFH + antler (250 mg/kg), ANFH + antler (500 mg/kg) and ANFH + antler (1,000 mg/kg) groups were treated with intraperitoneal injection of 250, 500 or 1,000 mg/kg antler extract/day, respectively, for 60 days. Serum samples were then extracted to determine total cholesterol (CT) and triglyceride levels, treat osteoblasts, measure 11β-HSD (11β-HSD1) and 11β-HSD2 and alkaline phosphatase (ALP) levels and cellular apoptosis, and determine the proportion of osteoblasts in each phase of the cell cycle. Serum CT and triglyceride levels in SANFH rabbits significantly decreased as the concentration of antler increased (P<0.05). 11β-HSD1 levels in the femoral heads of SANFH rabbits and osteoblasts following treatment with antler-containing serum decreased as the concentration of antler used increased, whereas levels of 11β-HSD1 increased significantly (P<0.05). The proliferation of osteoblasts and ALP levels in osteoblasts increased as the antler concentration increased, whereas the number of osteoblasts in the G0/G1 phase decreased significantly (P<0.05). The current study demonstrated that treatment with antler extract has a therapeutic effect on ANFH induced by steroids in rabbits and may regulate the expression of 11β-HSD in femoral heads and osteoblasts, as well as promoting the proliferation of osteoblasts.

Association of gene variants of transcription factors PPARγ, RUNX2, Osterix genes and COL2A1, IGFBP3 genes with the development of osteonecrosis of the femoral head in Chinese population

The molecular pathogenesis of osteonecrosis of the femoral head (ONFH) has been remained obscure so that its prevalence has been increasing in recent decades. Different transcription factors play critical roles in maintaining the balance between osteogenesis and adipogenesis. However, it has been unclear that the genes variants of the transcription factors exert the effects on the imbalance between steogenesis and adipogenesis during the development of ONFH. Here, we selected the 11SNPs from steogenesis, adipogenesis-specific transcription factors RUNX2, Osterix, and PPARγ genes, chondrogenesis or adipogenesis key factors COL2A1, IGFBP3 genes and analysed the genotypes, alleles, haplotypes and their association with the risk and clinical phenotypes of ONFH through Mass ARRAY® platformin in 200 ONFH patients and 177controls. The patients with ONFH (132 males, 68 females; age: 53.46±11.48yr) were consecutively enrolled at the Department of Orthopedics, the Second Clinical College of Jilin University, from March 2014 to June 2015 and were diagnosed and classified into 10 cases of stage II (5.6%), 54 cases of stage III (30.2%) and 115 cases (64.2%) of stage IV and alcohol-induced (71 cases (39.7%)), idiopathic (64 cases (34.0%)), and steroid-induced osteonecrosis (47 cases (26.3%)) subgroup, respectively. Our results showed that all models of logistical regression analysis, the co-dominants, dominants, and recessives of PPARγrs2920502, significantly associated with the increased risk of ONFH (p=0.004, p=0.013, p=0.016), respectively. Both the minor homozygous CC genotype and the allele C of rs2920502 were evidently correlated with the enhanced risk of ONFH (p=0.005, p=0.0005),respectively. The recessives models of IGFBP3rs2132572 (G/A) as well as RUNX2 rs3763190(G/A) were statistically associated with the higher ONFH risk, p=0.030, p=0.029, respectively; the minor homozygous(AA) of IGFBP3rs2132572 (G/A) was also related to the increased risk of bilateral hips lesions, p=0.039. Moreover, the ages on set of major homozygous(GG) and heterozygous(GT) of COL2A1rs2070739(G/A) were significantly younger than that of the minor homozygous(AA) of the SNP(p=0.008) while the A-T-G-A haplotype of COL2A1 gene revealed significant association with the decreased the risk of bilateral hip lesions, p=0.01, OR:0.258. More important, the serum HDL-c level and the ratio of LDL-c/HDL-c in the ONFH group were significantly decreased and increased compared with those of the control group (p=0.02, p=0.0001), respectively. Particularly, the CC genotype of PPARγ rs2920502 was statistically correlated with the enhanced serum TG level, p=0.011.These results suggest that the variants of PPARγ, RUNX2, COL2A1, and IGFBP3 genes closely associated with the development of ONFH.

Screening of the COL2A1 mutation in idiopathic osteonecrosis of the femoral head

Idiopathic osteonecrosis of the femoral head (idiopathic ONFH) is an ischemic disorder resulting in necrosis of the subchondral bone of the femoral head. COL2A1 mutations, including c.3508G>A, have been reported to be involved in its etiology. However, the etiological role of COL2A1 mutations in idiopathic ONFH remains controversial, because the pathology of idiopathic ONFH is ischemic necrosis, not epiphyseal dysplasia usually seen in the diseases caused by COL2A1 mutations. The purpose of this study is to examine whether COL2A1 mutations have causal relation with idiopathic ONFH or not. We recruited 1,451 Japanese patients with idiopathic ONFH, including steroid-, alcohol-, and neither steroid nor alcohol-associated (neither-associated) ONFH. The diagnosis was based on the criteria of the Japanese Research Committee on idiopathic ONFH of the Ministry of Health, Labour and Welfare. By whole-exome sequencing, entire COL2A1 coding regions and flanking introns were analyzed in 49 neither-associated ONFH patients. In addition, the c.3508G>A mutation of COL2A1 was checked in all idiopathic ONFH patients using the invader assay. Whole-exome sequencing did not detect any COL2A1 mutations in the 49 patients. The c.3508G>A mutation was not found in any of the 1,451 patients. In conclusion, COL2A1 is unlikely to cause idiopathic ONFH. Epiphyseal dysplasia of the femoral head caused by COL2A1 mutations may radiographically mimic idiopathic ONFH. COL2A1 mutations should prompt clinical re-evaluation of the patient's phenotype. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:768-774, 2017.

Reduced penetrance in a large Caucasian pedigree with Stickler syndrome

BACKGROUND

In a four-generation Caucasian family variably diagnosed with autosomal dominant (AD) Stickler or Wagner disease, commercial gene screening failed to identify a mutation in COL2A1 or VCAN. We utilized linkage mapping and exome sequencing to identify the causal variant.

MATERIALS AND METHODS

Genomic DNA samples collected from 40 family members were analyzed. A whole-genome linkage scan was performed using Illumina HumanLinkage-24 BeadChip followed by two-point and multipoint linkage analyses using FASTLINK and MERLIN. Exome sequencing was performed on two affected individuals, followed by co-segregation analysis.

RESULTS

Parametric multipoint linkage analysis using an AD inheritance model demonstrated HLOD scores > 2.00 at chromosomes 1p36.13-1p36.11 and 12q12-12q14.1. SIMWALK multipoint analysis replicated the peak in chromosome 12q (peak LOD = 1.975). FASTLINK two-point analysis highlighted several clustered chromosome 12q SNPs with HLOD > 1.0. Exome sequencing revealed a novel nonsense mutation (c.115C>T, p.Gln39*) in exon 2 of COL2A1 that is expected to result in nonsense-mediated decay of the RNA transcript. This mutation co-segregated with all clinically affected individuals and seven individuals who were clinically unaffected.

CONCLUSIONS

The utility of combining traditional linkage mapping and exome sequencing is highlighted to identify gene mutations in large families displaying a Mendelian inheritance of disease. Historically, nonsense mutations in exon 2 of COL2A1 have been reported to cause a fully penetrant ocular-only Stickler phenotype with few or no systemic manifestations. We report a novel nonsense mutation in exon 2 of COL2A1 that displays incomplete penetrance and/or variable age of onset with extraocular manifestations.

A Novel Regulatory Mechanism of Type II Collagen Expression via a SOX9-dependent Enhancer in Intron 6

Type II collagen α1 is specific for cartilaginous tissues, and mutations in its gene are associated with skeletal diseases. Its expression has been shown to be dependent on SOX9, a master transcription factor required for chondrogenesis that binds to an enhancer region in intron 1. However, ChIP sequencing revealed that SOX9 does not strongly bind to intron 1, but rather it binds to intron 6 and a site 30 kb upstream of the transcription start site. Here, we aimed to determine the role of the novel SOX9-binding site in intron 6. We prepared reporter constructs that contain a Col2a1 promoter, intron 1 with or without intron 6, and the luciferase gene. Although the reporter constructs were not activated by SOX9 alone, the construct that contained both introns 1 and 6 was activated 5-10-fold by the SOX9/SOX5 or the SOX9/SOX6 combination in transient-transfection assays in 293T cells. This enhancement was also observed in rat chondrosarcoma cells that stably expressed the construct. CRISPR/Cas9-induced deletion of intron 6 in RCS cells revealed that a 10-bp region of intron 6 is necessary both for Col2a1 expression and SOX9 binding. Furthermore, SOX9, but not SOX5, binds to this region as demonstrated in an electrophoretic mobility shift assay, although both SOX9 and SOX5 bind to a larger 325-bp fragment of intron 6 containing this small sequence. These findings suggest a novel mechanism of action of SOX5/6; namely, the SOX9/5/6 combination enhances Col2a1 transcription through a novel enhancer in intron 6 together with the enhancer in intron 1.

Endoplasmic reticulum stress in chondrodysplasias caused by mutations in collagen types II and X

The endoplasmic reticulum is primarily recognized as the site of synthesis and folding of secreted, membrane-bound, and some organelle-targeted proteins. An imbalance between the load of unfolded proteins and the processing capacity in endoplasmic reticulum leads to the accumulation of unfolded or misfolded proteins and endoplasmic reticulum stress, which is a hallmark of a number of storage diseases, including neurodegenerative diseases, a number of metabolic diseases, and cancer. Moreover, its contribution as a novel mechanistic paradigm in genetic skeletal diseases associated with abnormalities of the growth plates and dwarfism is considered. In this review, I discuss the mechanistic significance of endoplasmic reticulum stress, abnormal folding, and intracellular retention of mutant collagen types II and X in certain variants of skeletal chondrodysplasia.

Molecular genetics of the COL2A1-related disorders

Type II collagen, comprised of three identical alpha-1(II) chains, is the major collagen synthesized by chondrocytes, and is found in articular cartilage, vitreous humour, inner ear and nucleus pulposus. Mutations in the collagen type II alpha-1 gene (COL2A1) have been reported to be responsible for a series of abnormalities, known as type II collagenopathies. To date, 16 definite disorders, inherited in an autosomal dominant or recessive pattern, have been described to be associated with the COL2A1 mutations, and at least 405 mutations ranging from point mutations to complex rearrangements have been reported, though the underlying pathogenesis remains unclear. Significant clinical heterogeneity has been reported in COL2A1-associated type II collagenopathies. In this review, we highlight current knowledge of known mutations in the COL2A1 gene for these disorders, as well as genetic animal models related to the COL2A1 gene, which may help us understand the nature of complex phenotypes and underlying pathogenesis of these conditions.

Identification of a novel mutation of the COL2A1 gene in a Chinese family with spondyloepiphyseal dysplasia congenita

PURPOSE

To identify potential disease-causing mutation in the COL2A1 gene in a Chinese family with autosomal dominant spondyloepiphyseal dysplasia congenita (SEDC) and to analyze the phenotype-genotype correlation.

METHODS

Complete physical and radiographic examinations of four affected individuals from SEDC family were conducted. Genomic DNA were isolated from peripheral blood leukocytes. All 54 exons and exon-intron boundaries of the COL2A1 gene were amplified by polymerase chain reaction (PCR) and bidirectionally sequenced.

RESULTS

All four affected individuals were found carried a novel missense mutation of c.2224G>A (p.Gly687Ser) in COL2A1, while normal members of the family and 50 healthy controls did not have this mutation. Protein prediction of missense mutation by polyphen-2 and SIFT software and mutation taster indicated severe damage to the function.

CONCLUSIONS

c.2224G>A (p.Gly687Ser) is a novel mutation of COL2A1 associated with spondyloepiphyseal dysplasia congenital. There are heterozygous of phenotype for the mutation in members of the pedigree analyzed. Onset becomes more earlier and severe with each successive generation.

A genetic pedigree analysis to identify gene mutations involved in femoral head necrosis

The present study presents results from a linkage and mutation screening analysis aiming to identify the causative gene of femoral head necrosis, also known as osteonecrosis of femoral head (ONFH), in a Chinese pedigree. We collected clinical data on the osteonecrosis pedigree, and extracted blood and genomic DNA from the family members. Polymerase chain reaction (PCR) and direct sequencing allowed to identify a mutation in the COL2A1 gene of the proband; the clinical manifestations of the proband meet the criteria for osteonecrosis. The exons of COL2A1 were amplified by polymerase chain reaction and mutation screening was conducted by direct sequencing in all the family members. The locus was also sequenced in 50 unrelated healthy controls. The c.3665G>A heterozygous mutation was detected in patients of the pedigree, but not in healthy individuals. We conclude that a mutation in the COL2A1 gene is the causative agent of ONFH in this family. Therefore, this mutation may be associated with osteonecrosis in Chinese populations.

A novel p. Gly630Ser mutation of COL2A1 in a Chinese family with presentations of Legg-Calvé-Perthes disease or avascular necrosis of the femoral head

Objective

Mutations in the type II collagen gene are associated with certain human disorders, collectively termed type II collagenopathies. They include Legg–Calvé–Perthes disease (LCPD) and avascular necrosis of the femoral head (ANFH). These two diseases are skeletal dysplasias, inherited in an autosomal dominant fashion, characterized by groin pain, dislocation of the hip and diminished joint mobility. Coxa vara and elevation of the greater trochanter of the femur comprise the typical phenotype of LCPD, but do not occur in ANFH. Lack of synthesis of type II collagen and structural defects are responsible for the major clinical outcomes, because collagen is the essential matrix protein of all connective tissues. Type II collagen, encoded by the COL2A1 gene, contains N- and C- terminal regions that are cleaved after secretion into the extracellular matrix, and the core area is composed of a triple helical (Gly–X–Y) domain. If the Gly in this specific region is replaced by other amino acids, the structure of type II collagen will be destroyed.

Method

Forty-five members of a four-generation family were recruited and investigated. Diagnosis was made by independent orthopedic surgeons and radiologists. A mutation of the COL2A1 gene was detected.

Result

In our research, we identify a heterozygous mutation (c.1888 G>A, p. Gly630Ser) in exon 29 of COL2A1 in the Gly–X–Y domain, in a Chinese family affected by LCPD and ANFH. Our findings provide significant clues to the phenotype–genotype relationships in these syndromes and may be helpful in clinical diagnosis. Furthermore, these results should assist further studies of the mechanisms underlying collagen diseases.

Conclusion

Our data add new variants to the repertoire of COL2A1 mutation resulting in related collagenopathies.

Endoplasmic reticulum stress-unfolding protein response-apoptosis cascade causes chondrodysplasia in a col2a1 p.Gly1170Ser mutated mouse model

The collagen type II alpha 1 (COL2A1) mutation causes severe skeletal malformations, but the pathogenic mechanisms of how this occurs are unclear. To understand how this may happen, a col2a1 p.Gly1170Ser mutated mouse model was constructed and in homozygotes, the chondrodysplasia phenotype was observed. Misfolded procollagen was largely synthesized and retained in dilated endoplasmic reticulum and the endoplasmic reticulum stress (ERS)-unfolded protein response (UPR)-apoptosis cascade was activated. Apoptosis occurred prior to hypertrophy, prevented the formation of a hypertrophic zone, disrupted normal chondrogenic signaling pathways, and eventually caused chondrodysplasia. Heterozygotes had normal phenotypes and endoplasmic reticulum stress intensity was limited with no abnormal apoptosis detected. Our results suggest that earlier chondrocyte death was related to the ERS-UPR-apoptosis cascade and that this was the chief cause of chondrodysplaia. The col2a1 p.Gly1170Ser mutated mouse model offered a novel connection between misfolded collagen and skeletal malformation. Further investigation of this mouse mutant model can help us understand mechanisms of type II collagenopathies.

A mutation of the Col2a1 gene (G1170S) alters the transgenic murine phenotype and cartilage matrix homeostasis

BACKGROUND/PURPOSE

Genomic studies have revealed that there is a significant association between a point mutation of the human Col2A1 gene (G1170S) and several hip disorders. The purpose of the study was to explore the phenotype and altered cartilage matrix homeostasis of transgenic mice carrying this mutated Col2a1 gene.

METHODS

Wild-type and transgenic mice were used as the control and study groups, respectively. Body weight measurement, radiographic analysis, and histological analysis of the mice were carried out to describe differences between the wild-type and transgenic mice at different ages. Cartilage metabolism studies were also carried out, including an MTT assay of cellular proliferation and nitric oxide and glycosaminoglycan assays. Allelic expression levels of the mutant A allele and the normal G allele were established by TaqMan assay. Cytokine and protease gene expression were measured.

RESULTS

Transgenic mice had a lower mean body weight, a deformed skeletal structure, and abnormal cartilage histomorphology. Chondrocyte proliferation was significantly compromised and this was linked to significantly higher NO secretion and less soluble glycosaminoglycan formation. TNF-α and IL-1β gene expression was significantly upregulated, while MMP-13 gene expression was significantly downregulated.

CONCLUSION

The mutant G1170S Col2a1 gene in mice clearly alters the transgenic murine phenotype and cartilage matrix homeostasis.

Mutation-based growth charts for SEDC and other COL2A1 related dysplasias

From data collected via a large international collaborative study, we have constructed a growth chart for patients with molecularly confirmed congenital spondylo-epiphyseal dysplasia (SEDC) and other COL2A1 related dysplasias. The growth chart is based on longitudinal height measurements of 79 patients with glycine substitutions in the triple-helical domain of COL2A1. In addition, measurements of 27 patients with other molecular defects, such as arginine to cysteine substitutions, splice mutations, and mutations in the C-terminal propeptide have been plotted on the chart. Height of the patients progressively deviate from that of normal children: compared to normal WHO charts, the mean length/height is -2.6 SD at birth, -4.2 SD at 5 years, and -5.8 SD in adulthood. The mean adult height (male and female combined) of patients with glycine substitutions in the triple-helical region is 138.2 cm but there is a large variation. Patients with glycine to cysteine substitutions tend to cluster within the upper part of the chart, while patients with glycine to serine or valine substitutions are situated between +1 SD and -1 SD. Patients with carboxy-terminal glycine substitutions tend to be shorter than patients with amino-terminal substitutions, while patients with splice mutations are relatively tall. However, there are exceptions and specific mutations can have a strong or a relatively mild negative effect on growth. The observation of significant difference in adult height between affected members of the same family indicates that height remains a multifactorial trait even in the presence of a mutation with a strong dominant effect.

Premature osteoarthritis as presenting sign of type II collagenopathy: a case report and literature review

OBJECTIVES

Osteoarthritis (OA) is a frequent, chronic, and often disabling disease. Early-onset OA should prompt rheumatologists to search for underlying causes. We describe the clinical presentation and diagnosis of a patient with severe premature OA.

METHODS

We report a patient with severe polyarticular OA starting in young adulthood due to a heterozygous mutation in the COL2A1 gene. We discuss the clinical features, diagnosis, and known mutations of previously reported cases identified through a PubMed literature review.

RESULTS

A 43-year-old Caucasian woman of normal stature presented with a 24-year history of symmetrical polyarticular OA involving both large and small joints. At the time of presentation, the patient already underwent 6 joint replacement surgeries. Family history was unremarkable. Clinical, serologic, radiographic, and histologic studies did not reveal any specific cause for this unusual clinical presentation. Genetic analysis revealed a heterozygous COL2A1 mutation (R519C) consistent with the clinical phenotype. Reviewing the literature, we discuss the clinical spectrum of type II collagenopathies emphasizing premature OA as the sole clinical manifestation.

CONCLUSIONS

Unusual clinical presentations of OA should prompt investigations to search for an underlying cause. Type II collagenopathy should be considered in young adults with severe symmetrical OA even in the absence of other clinical features. A correct diagnosis allows classification and genetic counseling of the patient.

Pathophysiology and new strategies for the treatment of Legg-Calvé-Perthes disease

Legg-Calvé-Perthes disease is a juvenile form of idiopathic osteonecrosis of the femoral head that can lead to permanent femoral head deformity and premature osteoarthritis. According to two recent multicenter, prospective cohort studies, current nonoperative and operative treatments have modest success rates of producing a good outcome with a spherical femoral head in older children with Legg-Calvé-Perthes disease. Experimental studies have revealed that the immature femoral head is mechanically weakened following ischemic necrosis. Increased bone resorption and delayed new bone formation, in combination with continued mechanical loading of the hip, contribute to the pathogenesis of the femoral head deformity. Biological treatment strategies to improve the healing process by decreasing bone resorption and stimulating bone formation appear promising in nonhuman preclinical studies.

Clinical phenotypes associated with type II collagen mutations

COL2A1 mutations give rise to a spectrum of phenotypes predominantly affecting cartilage and bone from the severe disorders that are perinatally lethal to the milder conditions that are recognised in the post-natal period and childhood. The milder chondrodysplasias are characterised by disproportionate short stature, eye abnormalities, cleft palate and hearing loss. It remains poorly recognised that there is significant variability in the disease presentation, with early onset short stature conditions and later onset milder phenotypes. Similarly, it is under-acknowledged that COL2A1 mutations may solely cause joint disease in the absence of the other mentioned phenotypic clues. The underlying hypothesis is that there are novel phenotypes caused by mutations in type II collagen that extend from premature arthritis through to more severe bone dysplasias. The importance of finding a COL2A1 mutation lies in the subsequent ability to accurately assess recurrence risks and offer information regarding disease natural history. Most importantly, it enables at-risk individuals to be identified for implementation of preventative strategies and early ameliorative management of their condition. Such interventions potentially translate into a reduction in health costs associated with musculoskeletal disease.

Pseudoachondroplasia and multiple epiphyseal dysplasia: a 7-year comprehensive analysis of the known disease genes identify novel and recurrent mutations and provides an accurate assessment of their relative contribution

Pseudoachondroplasia (PSACH) and multiple epiphyseal dysplasia (MED) are relatively common skeletal dysplasias resulting in short-limbed dwarfism, joint pain, and stiffness. PSACH and the largest proportion of autosomal dominant MED (AD-MED) results from mutations in cartilage oligomeric matrix protein (COMP); however, AD-MED is genetically heterogenous and can also result from mutations in matrilin-3 (MATN3) and type IX collagen (COL9A1, COL9A2, and COL9A3). In contrast, autosomal recessive MED (rMED) appears to result exclusively from mutations in sulphate transporter solute carrier family 26 (SLC26A2). The diagnosis of PSACH and MED can be difficult for the nonexpert due to various complications and similarities with other related diseases and often mutation analysis is requested to either confirm or exclude the diagnosis. Since 2003, the European Skeletal Dysplasia Network (ESDN) has used an on-line review system to efficiently diagnose cases referred to the network prior to mutation analysis. In this study, we present the molecular findings in 130 patients referred to ESDN, which includes the identification of novel and recurrent mutations in over 100 patients. Furthermore, this study provides the first indication of the relative contribution of each gene and confirms that they account for the majority of PSACH and MED.

The epidemiology and demographics of legg-calvé-perthes' disease

The etiology of Legg-Calvé-Perthes' disease (LCPD) is unknown. There are many insights however from epidemiologic/demographic information. A systematic medical literature review regarding LCPD was performed. The incidence ranges from 0.4/100,000 to 29.0/100,000 children <15 years of age. There is significant variability in incidence within racial groups and is frequently higher in lower socioeconomic classes. The typical age at presentation ranges from 4 to 8 years (average 6.5 years), except for children from the Indian subcontinent (average 9.5 years). There is a mild familial component. The children demonstrate impaired growth in height, skeletal age, and birth weight. This impaired growth coincides with an age appropriate reduced somatomedin A activity and decreased levels of IGF. LCPD can be associated with abnormalities in the coagulation cascade, including an increase in factor V Leiden mutation, low levels of protein C and/or S, and decreased antithrombin activity. There is decreased turnover in type I collagen and synthesis of type III collagen, as well as reduced levels of urinary glycosaminoglycans in the active phases of the disorder. Subtle abnormalities in the opposite hip and other minor/major congenital defects are reported. Children with LCPD are active and score abnormally in certain standardized psychological tests.

Two novel COL2A1 mutations associated with a Legg-Calvé-Perthes disease-like presentation

BACKGROUND

Abnormal development and growth of the capital femoral epiphysis and acetabulum are associated with a wide variety of underlying etiologies, one of which is Legg-Calvé-Perthes disease.

CASE DESCRIPTION

We report the cases of two children who presented with abnormal development of both hips and in whom novel mutations in the COL2A1 gene were found. These cases illustrate the importance of identifying individuals with a type II collagen abnormality, as it informs management, allows investigation for other complications, and provides the opportunity for accurate genetic counseling and consideration of other family members who might be at risk.

LITERATURE REVIEW

The literature documents numerous private mutations in COL2A1 associated with diverse clinical phenotypes including bilateral hip dysplasia and premature osteoarthritis. Some of these mutations are associated with a joint-specific phenotype but few other skeletal or extraskeletal manifestations. Only careful clinical examination of children presenting with hip anomalies therefore will reveal additional findings that warrant an evaluation by a clinical geneticist. DNA mutation analysis may be useful for making a specific diagnosis and identifying other at-risk family members.

PURPOSES AND CLINICAL RELEVANCE

The purpose of our report is to alert clinicians to the possibility that children who present with bilateral Perthes-like disease of the hip might have an underlying mutation in the gene encoding type II collagen. It is important to consider this in the differential diagnosis and workup of such children as it has specific prognostic, clinical, genetic counseling, and reproductive sequelae.

Legg-Calvé-Perthes disease

Legg-Calvé-Perthes disease is an idiopathic hip disorder that produces ischemic necrosis of the growing femoral head. Permanent femoral head deformity is the most significant sequela. Experimental studies indicate that the pathologic repair process, which is marked by an imbalance of bone resorption and formation, contributes to the pathogenesis of femoral head deformity. Important prognostic factors include degree of deformity, age at disease onset, extent of head involvement, head-at-risk signs, and lateral pillar collapse. Treatment should be guided by age at disease onset, current best evidence, and prognostic factors. Patients aged <6 years at onset are best managed nonsurgically, whereas older patients may benefit from surgical treatment. Good surgical results have been reported in 40% to 60% of older patients (>8 years), indicating the need to develop more effective treatments based on the pathobiology of the disease.

Premature arthritis is a distinct type II collagen phenotype

Mutations in the gene encoding type II collagen (COL2A1) give rise to a spectrum of phenotypes predominantly affecting cartilage and bone. These chondrodysplasias are typically characterized by disproportionately short stature, eye abnormalities, cleft palate, and hearing loss. It is less recognized that mutations in COL2A1 can also present as degenerative joint disease in the absence of any other phenotypic clues. We report 2 Australian families presenting with an isolated arthritis phenotype, segregating as a dominant trait affecting both large and small joints, prior to age 30 years. Sequencing of COL2A1 in the propositi revealed 2 sequence changes resulting in glycine substitutions in the triple-helical domain of type II collagen. We review the increasing evidence implicating COL2A1 mutations in individuals presenting with isolated degenerative joint disease, aiming to alert physicians who assess these patients to this possibility. The importance of finding a COL2A1 mutation in such patients lies in the subsequent ability to accurately assess recurrence risks, offer early (including prenatal) diagnosis, and provide information regarding the natural history of the condition. Most importantly, it enables at-risk individuals to be identified for implementation of preventative strategies (i.e., weight loss, joint-friendly exercise programs) and early ameliorative management of their condition.