Evidence of association between GDF5 polymorphisms and congenital dislocation of the hip in a Caucasian population

Review of susceptibility genes in developmental dysplasia of the hip: A comprehensive examination of candidate genes and pathways

Developmental dysplasia of the hip (DDH) is one of the most prevalent skeletal deformities, primarily due to the incompatibility between the acetabulum and femoral head. It includes complete dislocation, partial dislocation, instability with femoral head subluxation, and a range of imaging abnormalities that reflect inadequate acetabular formation. Known risk factors for DDH include positive family history, sex, premature birth, non-cephalic delivery, oligohydramnios, gestational diabetes mellitus, maternal hypertension, associated anomalies, swaddling clothes, intrauterine space restriction, and post-term pregnancy. Various research designs have been employed in DDH studies to identify relevant genes, including candidate gene association studies (CGAS), genome-wide association studies (GWAS), restriction fragment length polymorphism (RFLP), and whole exome sequencing (WES). To date, multiple DDH-associated genes have been identified in various populations. Despite extensive research into the epidemiology, risk factors, and genes associated with DDH, its pathogenesis remains unclear. This study provides a comprehensive summary of DDH research designs and evidence for relevant gene mutations through a PubMed search.

Genetics of hip dysplasia - a systematic literature review

BACKGROUND

Developmental dysplasia of the hip (DDH) is a congenital condition affecting 2-3% of all newborns. DDH increases the risk of osteoarthritis and is the cause of 30% of all total hip arthroplasties in adults < 40 years of age. We aim to explore the genetic background of DDH in order to improve diagnosis and personalize treatment.

METHODS

We conducted a structured literature review using PRISMA guidelines searching the Medline, Embase and Cochrane databases. We included 31 case control studies examining single nucleotide polymorphisms (SNPs) in non-syndromic DDH.

RESULTS

A total of 73 papers were included for full text review, of which 31 were single nucleotide polymorphism (SNP) case/control association studies. The literature review revealed that the majority of published papers on the genetics of DDH were mostly underpowered for detection of any significant association. One large genome wide association study has been published (N = 9,915), establishing GDF5 as a plausible risk factor.

CONCLUSIONS

DDH is known to be congenital and heritable, with family occurrence of DDH already included as a risk factor in most screening programs. Despite this, high quality genetic research is scarce and no genetic risk factors have been soundly established, prompting the need for more research.

Molecular mechanisms and genetic factors contributing to the developmental dysplasia of the hip

The most prevalent hip disease in neonates is developmental dysplasia of the hip (DDH). A timely and accurate diagnosis is required to provide the most effective treatment for pediatric patients with DDH. Heredity and gene variation have been the subject of increased attention and research worldwide as one of the factors contributing to the pathogenesis of DDH. Genome-wide association studies (GWAS), genome-wide linkage analyses (GWLA), and exome sequencing (ES) have identified variants in numerous genes and single-nucleotide polymorphisms (SNPs) as being associated with susceptibility to DDH in sporadic and DDH family patients. Furthermore, the DDH phenotype can be observed in animal models that exhibit susceptibility genes or loci, including variants in CX3CR1, KANSL1, and GDF5. The dentification of noncoding RNAs and de novo gene variants in patients with DDH-related syndrome has enhanced our understanding of the genes implicated in DDH. This article reviews the most recent molecular mechanisms and genetic factors that contribute to DDH.

Environmental and Genetic Risk Factors in Developmental Dysplasia of the Hip for Early Detection of the Affected Population

Diagnosis of developmental dysplasia of the hip (DDH) mostly relies on physical examination and ultrasound, and both methods are operator-dependent. Late detection can lead to complications in young adults. Current evidence supports the involvement of environmental and genetic factors, such as single nucleotide variants (SNVs). Incorporating genetic factors into diagnostic methods would be useful for implementing early detection and management of affected individuals. Our aim was to analyze environmental factors and SNVs in DDH patients. We included 287 DDH cases and 284 controls. Logistic regression demonstrated an association for sex (OR 9.85, 95% CI 5.55-17.46, p = 0.0001), family history (OR 2.4, 95% CI 1.2-4.5, p = 0.006), fetal presentation (OR 3.19, 95% CI 1.55-6.54, p = 0.002), and oligohydramnios (OR 2.74, 95%CI 1.12-6.70, p = 0.026). A model predicting the risk of DDH including these variables showed sensitivity, specificity, PPV, and NPV of 0.91, 0.53, 0.74, and 0.80 respectively. The SNV rs1800470 in TGFB1 showed an association when adjusted for covariables, OR 0.49 (95% CI 0.27-0.90), p = 0.02. When rs1800470 was included in the equation, sensitivity, specificity, PPV and NPV were 0.90, 0.61, 0.84, and 0.73, respectively. Incorporating no-operator dependent variables and SNVs in detection methods could be useful for establishing uniform clinical guidelines and optimizing health resources.

Polymorphism rs143384 GDF5 reduces the risk of knee osteoarthritis development in obese individuals and increases the disease risk in non-obese population

BACKGROUND

We investigated the effect of obesity on the association of genome-wide associative studies (GWAS)-significant genes with the risk of knee osteoarthritis (KOA).

METHODS

All study participants (n = 1,100) were divided into 2 groups in terms of body mass index (BMI): BMI ≥ 30 (255 KOA patients and 167 controls) and BMI < 30 (245 KOA and 433 controls). The eight GWAS-significant KOA single nucleotide polymorphisms (SNP) of six candidate genes, such as LYPLAL1 (rs2820436, rs2820443), SBNO1 (rs1060105, rs56116847), WWP2 (rs34195470), NFAT5 (rs6499244), TGFA (rs3771501), GDF5 (rs143384), were genotyped. Logistic regression analysis (gPLINK online program) was used for SNPs associations study with the risk of developing KOA into 2 groups (BMI ≥ 30 and BMI < 30) separately. The functional effects of KOA risk loci were evaluated using in silico bioinformatic analysis.

RESULTS

Multidirectional relationships of the rs143384 GDF5 with KOA in BMI-different groups were found: This SNP was KOA protective locus among individuals with BMI ≥ 30 (OR 0.41 [95%CI 0.20-0.94] recessive model) and was disorder risk locus among individuals with BMI < 30 (OR 1.32 [95%CI 1.05-1.65] allele model, OR 1.44 [95%CI 1.10-1.86] additive model, OR 1.67 [95%CI 1.10-2.52] dominant model). Polymorphism rs143384 GDF5 manifested its regulatory effects in relation to nine genes (GDF5, CPNE1, EDEM2, ERGIC3, GDF5OS, PROCR, RBM39, RPL36P4, UQCC1) in adipose tissue, which were involved in the regulation of pathways of apoptosis of striated muscle cells.

CONCLUSIONS

In summary, the effect of obesity on the association of the rs143384 GDF5 with KOA was shown: the "protective" value of this polymorphism in the BMI ≥ 30 group and the "risk" meaning in BMI < 30 cohort.

Influence of Different Evolutive Forces on GDF5 Gene Variability

The GDF5 gene is involved in the development of skeletal elements, synovial joint formation, tendons, ligaments, and cartilage. Several polymorphisms are present within the gene, and two of them, rs143384 and 143383, were reported to be correlated with osteoarticular disease or muscle flexibility. The aim of this research is to verify if the worldwide distribution of the rs143384 polymorphism among human populations was shaped by selective pressure, or if it was the result of random genetic drift events. Ninety-four individuals of both the male and female sexes, 18-28 years old, from Sardinia were analyzed. We observed the following genotype frequencies: 28.72% of AA homozygotes, 13.83% of GG homozygotes, and 57.45% of AG heterozygotes. The allele frequencies were 0.574 for allele A and 0.426 for allele G. The relationships between the populations were verified via Multidimensional Scaling (MDS). Our data show (i) a clear heterogeneity within the African populations; (ii) a strong differentiation between the African populations and the other populations; and that (iii) the Sardinian population is placed within the European cluster. To reveal possible traces of selective pressure, the Population Branch Statistic (PBS) was calculated; both the rs143384 and 143383 SNPs have low PBS values, suggesting that there are no signals of selective pressure in those areas of the gene.

Genome-Wide Association Study and Transcriptome of Japanese Patients with Developmental Dysplasia of the Hip Demonstrates an Association with the Ferroptosis Signaling Pathway

This study examined the association between developmental dysplasia of the hip (DDH) and disease-associated loci in a Japanese cohort. A genome-wide association study (GWAS) of 238 Japanese patients with DDH and 2044 healthy individuals was performed. As a replicate, GWAS was also conducted on the UK Biobank data with 3315 cases and matched 74,038 controls. Gene set enrichment analyses (GSEAs) of both the genetics and transcriptome of DDH were performed. Transcriptome analysis of cartilage specimens from DDH-associated osteoarthritis and femoral neck fractures was performed as a control. Most of the lead variants were very low-frequency ones in the UK, and variants in the Japanese GWAS could not be replicated with the UK GWAS. We assigned DDH-related candidate variants to 42 and 81 genes from the Japanese and UK GWASs, respectively, using functional mapping and annotation. GSEA of gene ontology, disease ontology, and canonical pathways identified the most enriched pathway to be the ferroptosis signaling pathway, both in the Japanese gene set as well as the Japanese and UK merged set. Transcriptome GSEA also identified significant downregulation of genes in the ferroptosis signaling pathway. Thus, the ferroptosis signaling pathway may be associated with the pathogenic mechanism of DDH.

Developmental dysplasia of the hip: A systematic review of susceptibility genes and epigenetics

BACKGROUND

Developmental dysplasia of the hip (DDH) is a complex developmental deformity whose pathogenesis and susceptibility-related genes have yet to be elucidated. This systematic review summarizes the current literature on DDH-related gene mutations, animal model experiments, and epigenetic changes in DDH.

METHODS

We performed a comprehensive search of relevant documents in the Medline, Scopus, Cochrane, and ScienceDirect databases covering the period from October 1991 to October 2021. We analyzed basic information on the included studies and summarized the DDH-related mutation sites, animal model experiments, and epigenetic changes associated with DDH.

RESULTS

A total of 63 studies were included in the analysis, of which 54 dealt with the detection of gene mutations, 7 presented details of animal experiments, and 6 were epigenetic studies. No genetic mutations were clearly related to the pathogenesis of DDH, including the most frequently studied genes on chromosomes 1, 17, and 20. Most gene-related studies were performed in Han Chinese or North American populations, and the quality of these studies was medium or low. GDF5 was examined in the greatest number of studies, and mutation sites with odds ratios > 10 were located on chromosomes 3, 9, and 13. Six mutations were found in animal experiments (i.e., CX3CR1, GDF5, PAPPA2, TENM3, UFSP2, and WISP3). Epigenetics research on DDH has focused on GDF5 promoter methylation, three microRNAs (miRNAs), and long noncoding RNAs. In addition, there was also a genetic test for miRNA and mRNA sequencing.

CONCLUSIONS

DDH is a complex joint deformity with a considerable genetic component whose early diagnosis is significant for preventing disease. At present, no genes clearly involved in the pathogenesis of DDH have been identified. Research on mutations associated with this condition is progressing in the direction of in vivo experiments in animal models to identify DDH susceptibility genes and epigenetics analyses to provide novel insights into its pathogenesis. In the future, genetic profiling may improve matters.

Whole exome sequencing of 28 families of Danish descent reveals novel candidate genes and pathways in developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is a common condition involving instability of the hip with multifactorial etiology. Early diagnosis and treatment are critical as undetected DDH is an important cause of long-term hip complications. Better diagnostics may be achieved through genetic methods, especially for patients with positive family history. Several candidate genes have been reported but the exact molecular etiology of the disease is yet unknown. In the present study, we performed whole exome sequencing of DDH patients from 28 families with at least two affected first-degree relatives. Four genes previously not associated with DDH (METTL21B, DIS3L2, PPP6R2, and TM4SF19) were identified with the same variants shared among affected family members, in more than two families. Among known association genes, we found damaging variants in DACH1, MYH10, NOTCH2, TBX4, EVC2, OTOG, and SHC3. Mutational burden analysis across the families identified 322 candidate genes, and enriched pathways include the extracellular matrix, cytoskeleton, ion-binding, and detection of mechanical stimulus. Taken altogether, our data suggest a polygenic mode of inheritance for DDH, and we propose that an impaired transduction of the mechanical stimulus is involved in the etiopathological mechanism. Our findings refine our current understanding of candidate causal genes in DDH, and provide a foundation for downstream functional studies.

Comprehensive bioinformatics analysis of susceptibility genes for developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is a multifactorial disease, which occurs under environmental and genetic influence. The etiopathogenesis of DDH has not been fully explained. As research progresses, many candidate genes have been found to be closely related to the occurrence of DDH. In this study, we comprehensively examined 16 susceptibility genes of DDH using bioinformatics. COL1A1 encodes the pro-alpha1 chains of type I collagen, which is the major protein component of the bone extracellular matrix (ECM). The genes displaying the most statistically significant co-expression link to COL1A1 are ASPN, TGFB1, DKK1, IL-6, TENM3 and GDF5. DKK1, FRZB and WISP3 are components of the Wnt signaling pathway. CX3CR1 and GDF5 regulate chondrogenesis through the canonical Wnt signaling pathway. ASPN could induce collagen mineralization through binding with collagen and calcium. Integrated bioinformatics analysis indicates that ECM, Wnt signaling pathway and TGF-β signaling pathway are involved in the occurrence of DDH. These provide a basis for further exploring the pathogenesis of DDH.

Genetic Study of IL6, GDF5 and PAPPA2 in Association with Developmental Dysplasia of the Hip

Background: Developmental dysplasia of the hip (DDH) is one of the most prevalent skeletal disorders. DDH is considered a pathologic condition with polygenic background, but environmental and mechanic factors significantly contribute to its multifactorial etiology. Inheritance consistent with autosomal dominant type has also been observed. Single-nucleotide polymorphisms (SNPs) in various genes mostly related to formation of connective tissue are studied for a possible association with DDH. Methods: We genotyped three SNPs, rs1800796 located in the promoter region of the IL6 gene, rs143383 located in the 5′ untranslated region (UTR) of the GDF5 gene and rs726252 located in the fifth intron of the PAPPA2 gene. The study consisted of 45 subjects with DDH and 85 controls from all regions of Slovakia. Results: Association between DDH occurrence and studied genotypes affected by aforementioned polymorphisms was confirmed in the case of rs143383 in the GDF5 gene (p = 0.047), where the T allele was over-expressed in the study group. Meanwhile, in the matter of IL6 and PAPPA2, we found no association with DDH (p = 0.363 and p = 0.478, respectively). Conclusions: These results suggest that there is an association between DDH and GDF5 polymorphisms and that the T allele is more frequently presents in patients suffering from DDH.

Secreted frizzled-related protein 3 was genetically and functionally associated with developmental dysplasia of the hip

Background: Developmental dysplasia of the hip (DDH) is the most common joint disease in child orthopedics. Secreted Frizzled-Related Protein 3 (FRZB) plays an important role in joint development. however, no direct association between FRZB and DDH has been demonstrated.

Methods: Analysis of genotype distribution and allele frequency for detected single nucleotide polymorphisms (SNP) of FRZB was performed. FRZB expression was assayed in DDH joint tissues. Further experiments to identify the chondrogenic properties of FRZB were conducted. Potential upstream miRNAs for FRZB were assayed in DDH.

Results: Significant difference in genotype distribution for rs3768842 (OR=1.46, P=0.0081) and rs2242040 (OR=0.65, P=0.0067) was found. DDH joint tissues showed significantly higher FRZB expression. FRZB demonstrated chondrogenic and anti-hypertrophic properties in vitro. FRZB modulated cell adhesion pathway and cell spreading by regulating integrins expressions. Upstream miRNAs regulating FRZB expression were identified in DDH synovial fluid. Experiments indicated that downregulated miRNA-454 caused FRZB upregulation in DDH joint.

Conclusion: Dysregulated FRZB and its loci were associated with DDH. As a Wnt antagonist with chondrogenic properties, FRZB modulated cell adhesion pathway and cell spreading by regulating integrins expressions. FRZB in multiple DDH joint tissues might be mediated by the dysregulated miRNA expression profiles in the joint synovial fluid.

Making and shaping endochondral and intramembranous bones

Skeletal elements have a diverse range of shapes and sizes specialized to their various roles including protecting internal organs, locomotion, feeding, hearing, and vocalization. The precise positioning, size, and shape of skeletal elements is therefore critical for their function. During embryonic development, bone forms by endochondral or intramembranous ossification and can arise from the paraxial and lateral plate mesoderm or neural crest. This review describes inductive mechanisms to position and pattern bones within the developing embryo, compares and contrasts the intrinsic vs extrinsic mechanisms of endochondral and intramembranous skeletal development, and details known cellular processes that precisely determine skeletal shape and size. Key cellular mechanisms are employed at distinct stages of ossification, many of which occur in response to mechanical cues (eg, joint formation) or preempting future load‐bearing requirements. Rapid shape changes occur during cellular condensation and template establishment. Specialized cellular behaviors, such as chondrocyte hypertrophy in endochondral bone and secondary cartilage on intramembranous bones, also dramatically change template shape. Once ossification is complete, bone shape undergoes functional adaptation through (re)modeling. We also highlight how alterations in these cellular processes contribute to evolutionary change and how differences in the embryonic origin of bones can influence postnatal bone repair.

Compares and contrasts Endochondral and intramembranous bone development

Reviews embryonic origins of different bones

Describes the cellular and molecular mechanisms of positioning skeletal elements.

Describes mechanisms of skeletal growth with a focus on the generation of skeletal shape

Genetics of developmental dysplasia of the hip

In the last decade, the advances in the molecular analyses and sequencing techniques allowed researchers to study developmental dysplasia of the hip (DDH) more thoroughly. Certain chromosomes, genes, loci and polymorphisms are being associated with variable severity of this disorder. The wide range of signs and symptoms is dependent either on isolated or systemic manifestation. Phenotypes of isolated cases range from only a mild ligamental laxity, through subluxation, to a complete dislocation of the femoral head. Systemic manifestation is connected to various forms of skeletal dysplasia and other malformations characterized by significant genetic aberrations. To reveal the background of DDH heredity, multiple studies focused on large sample sizes with an emphasis on the correlation between genotype, phenotype and continuous clinical examination. Etiological risk factors that have been observed and documented in patients include genetic, environmental, and mechanical factors, which significantly contribute to the familial or nonfamilial occurrence and phenotypic variability of this disorder. Still, the multifactorial etiology and pathogenesis of DDH are not yet sufficiently clarified, explained, or understood. Formation of connective tissue, osteogenesis, chondrogenesis, and all other affected pathways and variations in the function of their individual elements contribute to the creation of the pathology in a developing human body. This review article presents an up-to-date list of known DDH associated genes, their products, and functional characteristics.

Developmental Dysplasia of the Hip: A Review of Etiopathogenesis, Risk Factors, and Genetic Aspects

As one of the most frequent skeletal anomalies, developmental dysplasia of the hip (DDH) is characterized by a considerable range of pathology, from minor laxity of ligaments in the hip joint to complete luxation. Multifactorial etiology, of which the candidate genes have been studied the most, poses a challenge in understanding this disorder. Candidate gene association studies (CGASs) along with genome-wide association studies (GWASs) and genome-wide linkage analyses (GWLAs) have found numerous genes and loci with susceptible DDH association. Studies put major importance on candidate genes associated with the formation of connective tissue (COL1A1), osteogenesis (PAPPA2, GDF5), chondrogenesis (UQCC1, ASPN) and cell growth, proliferation and differentiation (TGFB1). Recent studies show that epigenetic factors, such as DNA methylation affect gene expression and therefore could play an important role in DDH pathogenesis. This paper reviews all existing risk factors affecting DDH incidence, along with candidate genes associated with genetic or epigenetic etiology of DDH in various studies.

Genetic Predisposition to Developmental Dysplasia of the Hip

BACKGROUND

The etiopathogenesis of developmental dysplasia of the hip (DDH) has not been clarified. This systematic review evaluated current literature concerning all known chromosomes, loci, genes, and their polymorphisms that have been associated or not with the prevalence and severity of DDH.

METHODS

Following the established methodology of Meta-analysis of Observational Studies in Epidemiology guidelines, MEDLINE, EMBASE, and Cochrane Register of Controlled Trials were systematically searched from inception to January 2019.

RESULTS

Forty-five studies were finally included. The majority of genetic studies were candidate gene association studies assessing Chinese populations with moderate methodological quality. Among the most frequently studied are the first, third, 12th,17th, and 20th chromosomes. No gene was firmly associated with DDH phenotype. Studies from different populations often report conflicting results on the same single-nucleotide polymorphism (SNP). The SNP rs143384 of GDF5 gene on chromosome 20 demonstrated the most robust relationship with DDH phenotype in association studies. The highest odds of coinheritance in linkage studies have been reported for regions of chromosome 3 and 13. Five SNPs have been associated with the severity of DDH. Animal model studies validating previous human findings provided suggestive evidence of an inducing role of mutations of the GDF5, CX3CR1, and TENM3 genes in DDH etiopathogenesis.

CONCLUSION

DDH is a complex disorder with environmental and genetic causes. However, no firm correlation between genotype and DDH phenotype currently exists. Systematic genome evaluation in studies with larger sample size, better methodological quality, and assessment of DDH patients is necessary to clarify the DDH heredity. The role of next-generation sequencing techniques is promising.

Developmental dysplasia of the hip: a systematic literature review of the genes related with its occurrence

Developmental dysplasia of the hip (DDH) is one of the most prevalent congenital malformations. It has a wide spectrum of anatomical abnormalities of the hip joint and is characterized by mild or incomplete formation of the acetabulum leading to laxity of the joint capsule, secondary deformity of the proximal femur and irreducible hip dislocation. It is the leading cause of early hip osteoarthritis in young individuals.

Both genetic and environmental factors have been proposed to play an important role in the pathogenesis of DDH. A high prevalence is present in Asian, Caucasian, Mediterranean and American populations, with females being more frequently affected. We evaluated a variety of genetic studies indexed in the PubMed database.

Several susceptive genes, including WISP3, PAPPA2, HOXB9, HOXD9, GDF5, TGF Beta 1, CX3CR1, UQCC, COL1A1, TbX4 and ASPN have been identified as being associated with the development of DDH. Moreover, genetic association has also been reported between hip dysplasia and other comorbidities. Even though genetic components are a crucial part in the aetiology of DDH, several DDH susceptibility genes need further investigation.

The purpose of this review is to present current literature evidence regarding genes responsible for DDH development.

Cite this article: EFORT Open Rev 2019;4:595-601. DOI: 10.1302/2058-5241.4.190006

3D-bioprinting a genetically inspired cartilage scaffold with GDF5-conjugated BMSC-laden hydrogel and polymer for cartilage repair

Rationale: Articular cartilage injury is extremely common in congenital joint dysplasia patients. Genetic studies have identified Growth differentiation factor 5 (GDF5) as a shared gene in joint dysplasia and OA progression across different populations. However, few studies have employed GDF5 in biological regeneration for articular cartilage repair. Methods & Results: In the present study, we report identified genetic association between GDF5 loci and hip joint dysplasia with genome-wide association study (GWAS). GWAS and replication studies in separate populations achieved significant signals for GDF5 loci. GDF5 expression was dysregulated with allelic differences in hip cartilage of DDH and upregulated in the repaired cartilage in a rabbit cartilage defect model. GDF5 in vitro enhanced chondrogenesis and migration of bone marrow stem cells (BMSCs), GDF5 was tested in ectopic cartilage generation with BMSCs by GDF5 in nude mice in vivo. Genetically inspired, we further generated functional knee articular cartilage construct for cartilage repair by 3d-bioprinting a GDF5-conjugated BMSC-laden scaffold. GDF5-conjugated scaffold showed better cartilage repairing effects compared to control. Meanwhile, transplantation of the 3D-bioprinted GDF5-conjugated BMSC-laden scaffold in rabbit knees conferred long-term chondroprotection. Conclusions: In conclusion, we report identified genetic association between GDF5 and DDH with combined GWAS and replications, which further inspired us to generate a ready-to-implant GDF5-conjugated BMSC-laden scaffold with one-step 3d-bioprinting for cartilage repair.

DNA hypermethylation of GDF5 in developmental dysplasia of the hip (DDH)

INTRODUCTION & OBJECTIVE

Developmental Dysplasia of the Hip (DDH) is one of the most common congenital skeletal anomalies. Body of evidence suggests that genetic variations in GDF5 are associated with susceptibility to DDH. DDH is a multifactorial disease and its etiology has not been entirely determined. Epigenetic changes such as DNA methylation could be linked to DDH. In this scheme, we hypothesized that changes in GDF5 DNA methylation could predispose a susceptible individual to DDH.

METHODS

This study consisted of 45 DDH patients and 45 controls with healthy femoral neck cartilage, who underwent hemi-, or total arthroplasty for the femoral neck fracture. A cartilage sample of 1 cm in diameter and 1 mm in the thickness was obtained for DNA extraction. DNA was extracted and DNA methylation of GDF5 was evaluated by metabisulfite method.

RESULTS

Methylation analysis showed that the promoter of GDF5 in cartilage samples from DDH patients was hypermethylated in comparison to healthy controls (p = .001).

CONCLUSION

Our study showed that the methylation status of the GDF5 in patients with DDH is dysregulated. This dysregulation indicates that adjustment in the methylation might modify the expression of this gene. Since this gene plays an essential role in cartilage and bone development, thus reducing its expression can contribute to the pathogenesis of DDH. Further studies are needed to elucidate the role of GDF5 in this disease.

Developmental Dysplasia of Hip: Perspectives in Genetic Screening

Development dysplasia of the hip (DDH) is a complex developmental disorder despite being a relatively common condition mainly caused by incompatibility of the femoral head and the abnormal joint socket. Development dysplasia of the hip describes a wide spectrum of disorders ranging from minor acetabular dysplasia to irreducible dislocation of the hip. Modern medicine still suffers from lack of information about screening and precise genetic examination. Genome wide linkage and association studies have brought significant progress to DDH diagnosis. Association studies managed to identify many candidate (susceptible) genes, such as PAPPA2, COL2A1, HOXD9, GDF-5, and TGFB1, which play a considerable role in the pathogenesis of DDH. Early detection of DDH has a big chance to help in preventing further disability and improve the psychological health and quality of life in those children. This emphasizes the importance to establish a universal screening program along with the genetic counseling.

The role of Gdf5 regulatory regions in development of hip morphology

Given GDF5 involvement in hip development, and osteoarthritis (OA) and developmental hip dysplasia (DDH) risk, here we sought to assess the role(s) of GDF5 and its regulatory sequence on the development of hip morphology linked to injury risk. The brachypodism (bp) mouse, which harbors a Gdf5 inactivating mutation, was used to survey how Gdf5 loss of function impacts the development of hip morphology. Two transgenic Gdf5 reporter BAC lines were used to assess the spatiotemporal expression of Gdf5 regulatory sequences. Each BAC line was also used to assess the functional roles of upstream and downstream sequence on hip morphology. bp/bp mice had shorter femora with smaller femoral heads and necks as well as larger alpha angles, smaller anterior offsets, and smaller acetabula, compared to bp/+ mice (p<0.04). Regulatory sequences downstream of Gdf5 drove strong prenatal (E17) expression and low postnatal (6 months) expression across regions of femoral head and acetabulum. Conversely, upstream regulatory sequences drove very low expression at E17 and no detectable expression at 6 months. Importantly, downstream, but not upstream Gdf5 regulatory sequences fully restored all the key morphologic features disrupted in bp/bp mice. Hip morphology is profoundly affected by Gdf5 absence, and downstream regulatory sequences mediate its effects by controlling Gdf5 expression during development. This downstream region contains numerous enhancers harboring risk variants related to hip OA, DDH, and dislocation. We posit that subtle alterations to morphology driven by changes in downstream regulatory sequence underlie this locus’ role in hip injury risk.

Genome-wide association study of developmental dysplasia of the hip identifies an association with GDF5

Developmental dysplasia of the hip (DDH) is the most common skeletal developmental disease. However, its genetic architecture is poorly understood. We conduct the largest DDH genome-wide association study to date and replicate our findings in independent cohorts. We find the heritable component of DDH attributable to common genetic variants to be 55% and distributed equally across the autosomal and X-chromosomes. We identify replicating evidence for association between GDF5 promoter variation and DDH (rs143384, effect allele A, odds ratio 1.44, 95% confidence interval 1.34–1.56, P = 3.55 × 10⁻²²). Gene-based analysis implicates GDF5 (P = 9.24 × 10⁻¹²), UQCC1 (P = 1.86 × 10⁻¹⁰), MMP24 (P = 3.18 × 10⁻⁹), RETSAT (P = 3.70 × 10⁻⁸) and PDRG1 (P = 1.06 × 10⁻⁷) in DDH susceptibility. We find shared genetic architecture between DDH and hip osteoarthritis, but no predictive power of osteoarthritis polygenic risk score on DDH status, underscoring the complex nature of the two traits. We report a scalable, time-efficient recruitment strategy and establish for the first time to our knowledge a robust DDH genetic association locus at GDF5.

Konstantinos Hatzikotoulas et al. report the largest genome-wide association study to date for developmental dysplasia of the hip using national clinical audit data from the UK. They find a significant association with the GDF5 locus and evidence for shared genetic architecture with hip osteoarthritis.

Genetic Influence in Developmental Dysplasia of the Hip in Saudi Arabian Children Due to GDF5 Polymorphism

Developmental dysplasia of the hip (DDH) is quite common among Saudi Arabian babies. With an objective to assess the presence of SNP rs143383 and the alleles in the GDF5 gene among patients with DDH, parents, and unaffected siblings, we undertook this case-controlled study. We collected and analyzed for a functional single nucleotide polymorphism (SNP) in the 5'-untranslated region of the GDF5 gene (rs143383), 473 blood samples, (100 patients, 200 parents, 73 siblings and 100 healthy controls. We determined the association between the patients' genotype and their fathers', mothers' and siblings' genotype through Chi-square analysis. The majority of those screened possessed the TC genotype, and 61.8% of patients and their fathers had the TT genotype. There was no association between patients' and fathers' genotype, P value < 0.332, 95% CI (0.328-0.346), and between patients' and mothers', P < 0.006, 95% CI (0.004-0.007). When considering DDH patients' and the control group's genotypes, the odds ratios of TT versus other combined (0.641 > 1) and CC versus other combined (0.474 < 1) revealed that the TT genotype has higher risk of developing DDH compared with the CC genotype. The 95 percent confidence interval of TT versus other combined and CC versus other combined is 0.932-2.891 and 0.208-1.078, respectively. For patients' and fathers' genotypes, the odds ratios of TT versus other combined (1.275 > 1) and CC versus other combined (0.815 < 1) indicate that the TT genotype has higher risk of exhibiting DDH compared to the CC genotype. For patients' and siblings' genotypes, the odds ratios of TT versus other combined (1.669) and CC versus other combined (1.048) specify that the TT genotype possesses higher risk of developing DDH compared with the CC genotype. Our study shows that there exists a relationship between GDF5 (SNP rs143383) and DDH in our population. Second, we found for the first time that the genotype TT and the T allele were overly expressed in the patients and the fathers. More studies on the confirmation of this genetic marker for DDH are called for.

Pathways to understanding the genomic aetiology of osteoarthritis

Osteoarthritis is a common, complex disease with no curative therapy. In this review, we summarize current knowledge on disease aetiopathogenesis and outline genetics and genomics approaches that are helping catalyse a much-needed improved understanding of the biological underpinning of disease development and progression.

Severe cartilage degeneration in patients with developmental dysplasia of the hip

Developmental dysplasia of the hip (DDH) is a developmental disorder that has long-term chronic pain and limited hip joint mobility as major pathological characteristics. This study aims to access the association between the development of DDH and cartilage metabolic disorders. Cartilage tissue samples were acquired from patients with DDH, osteoarthritis (OA) and femoral neck fracture. The proteoglycan level was evaluated by safranin O-fast green, toluidine blue and hematoxylin-eosin (HE) staining. The levels of collagen-II (Col-II), collagen-X (Col-X) and metal matrix proteinase-13 (MMP-13) were evaluated by immunohistochemistry (IHC) and Western blotting analysis. The morphologic evaluation of cartilage was conducted by transmission electron microscopy (TEM). Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect the mRNA level of aggrecan, Col-II, Col-X and MMP-13. The aggrecan level in the cartilage matrix was significantly decreased in DDH patients by safranin O-fast green and toluidine blue staining in comparison with that in the OA and control groups. In contrast with the OA group, the Col-II expression was reduced while the MMP-13 expression increased in DDH patients, as shown by IHC and Western blotting analysis. The collagenous fibrils in cartilage of DDH patients appeared significantly sparse and disordered in the TEM analysis. In DDH patients, the mRNA expression levels of Col-II and aggrecan were markedly reduced, while the mRNA expression of Col-X was markedly increased, compared with the OA patients. There is severe articular cartilage degeneration in DDH patients. This observation provides us with new insight into cartilage metabolic regulation in DDH. © 2017 IUBMB Life, 69(3):179-187, 2017.

Prospective cohort study of the risk factors for stress fractures in Chinese male infantry recruits

Objective

To determine potential risk factors that could predict stress fractures over an 8-week basic military training in Chinese male infantry recruits.

Methods

Recruits from three infantry units enrolled in this prospective study. At baseline, demographic data, personal history of stress fractures, mean duration of weekly exercise and smoking history were recorded on questionnaires and blood samples taken for analysis of bone turnover biomarkers and genetic factors.

Results

Of the 1516 male recruits who volunteered to participate in the study, 1398 recruits provided data for analysis. In total, 189 stress fracture cases were observed (incidence rate: 13.5%) during the 8-week training period. Recruits with stress fractures had a significantly higher incidence of prior fracture history and lower exercise level prior to enrolment compared with those without stress fractures. A significant difference in both allelic frequency and genotypic distribution of the growth differentiation factor 5 (GDF5) gene rs143383 polymorphism was observed between recruits with and without stress fractures. However, no difference in serum bone turnover biomarkers was detected between groups.

Conclusion

This prospective, cohort study indicates that fracture history, lower exercise level and GDF5 rs143383 may be predictive risk factors for stress fractures in Chinese male infantry recruits.

Analysis of genetics and DNA methylation in osteoarthritis: What have we learnt about the disease?

Osteoarthritis (OA) is a chronic musculoskeletal disease characterised by the destruction of articular cartilage, synovial inflammation and bone remodelling. Disease aetiology is complex and highly heritable, with genetic variation estimated to contribute to 50% of OA occurrence. Epigenetic alterations, including DNA methylation changes, have also been implicated in OA pathophysiology. This review examines what genetic and DNA methylation studies have taught us about the genes and pathways involved in OA pathology. The influence of DNA methylation on the molecular mechanisms underlying OA genetic risk and the consequence of this interaction on disease susceptibility and penetrance are also discussed.

Overexpression of MMP13 in human osteoarthritic cartilage is associated with the SMAD-independent TGF-β signalling pathway

Introduction

In vitro and animal model of osteoarthritis (OA) studies suggest that TGF-β signalling is involved in OA, but human data is limited. We undertook this study to elucidate the role of TGF-β signalling pathway in OA by comparing the expression levels of TGFB1 and BMP2 as ligands, SMAD3 as an intracellular mediator, and MMP13 as a targeted gene between human osteoarthritic and healthy cartilage.

Methods

Human cartilage samples were collected from patients undergoing total hip/knee joint replacement surgery due to primary OA or hip fractures as controls. RNA was extracted from the cartilage tissues. Real-time quantitative PCR was performed to measure gene expression. Mann-Whitney test was utilized to compare the expression levels of TGFB1, BMP2, SMAD3 and MMP13 in human cartilage between OA cases and controls. Spearman’s rank correlation coefficient (rho) was calculated to examine the correlation between the expression levels of the four genes studied and non-parametric regression was used to adjust for covariates.

Results

A total of 32 OA cases (25 hip OA and 7 knee OA) and 21 healthy controls were included. The expression of TGFB1, SMAD3, and MMP13 were on average 70 %, 46 %, and 355 % higher, respectively, whereas the expression of BMP2 was 88 % lower, in OA-affected cartilage than that of controls (all p < 0.03), but no difference was observed between hip and knee OA (all p > 0.4). The expression of TGFB1 was correlated with the expression of SMAD3 (rho = 0.50, p = 0.003) and MMP13 (rho = 0.46, p = 0.007) in OA-affected cartilage and the significance became stronger after adjustment for age, sex, and BMI. The expression of BMP2 was negatively correlated with both TGFB1 (rho = −0.50, p = 0.02) and MMP13 (rho = −0.48, p = 0.02) in healthy cartilage, but the significance was altered after adjustment for the covariates. There was no correlation between the expression of SMAD3 and MMP13.

Conclusions

Our results demonstrate that MMP13 expression is associated with an increased expression of TGFB1 in OA-affected cartilage, possibly through SMAD-independent TGF-β pathway. Furthermore, TGF-β/SMAD3 is overactivated in OA cartilage; yet, the consequence of this overactivation remains to be established.

CpG methylation regulates allelic expression of GDF5 by modulating binding of SP1 and SP3 repressor proteins to the osteoarthritis susceptibility SNP rs143383

GDF5 encodes an extracellular signalling molecule that is essential for normal skeletal development. The rs144383 C to T SNP located in the 5'UTR of this gene is functional and has a pleiotropic effect on the musculoskeletal system, being a risk factor for knee-osteoarthritis (OA), congenital hip dysplasia, lumbar disc degeneration and Achilles tendon pathology. rs143383 exerts a joint-wide effect on GDF5 expression, with expression of the OA-associated T allele being significantly reduced relative to the C allele, termed allelic expression imbalance. We have previously reported that the GDF5 locus is subject to DNA methylation and that allelic imbalance of rs143383 is mediated by SP1, SP3 and DEAF1 transcriptional repressors. In this study, we have assayed GDF5 methylation in normal and osteoarthritic cartilage, and investigated the effect of methylation on the allelic imbalance of rs143383. We observed demethylation of the GDF5 5'UTR in OA knee cartilage relative to both OA (p = 0.009) and non-OA (p = 0.001) hip cartilage, with the most significant demethylation observed at the highly conserved +37 CpG site located 4 bp upstream of rs143383. Methylation modulates the level and direction of allelic imbalance of rs143383, with methylation of the +37 CpG dinucleotide within the SP1/SP3 binding site having an allele-specific effect on SP1 and SP3 binding. Furthermore, methylation attenuated the repressive effects of SP1, SP3 and DEAF1 on GDF5 promoter activity. This data suggest that the differential methylation of the +37 CpG site between osteoarthritic hip and knee cartilage may be responsible for the knee-specific effect of rs143383 on OA susceptibility.

A replication study for the association of rs726252 in PAPPA2 with developmental dysplasia of the hip in Chinese Han population

Developmental dysplasia of the hip (DDH) is a common developmental hip disorder, which ranges from mild acetabulum malformation to irreducible hip dislocation. A previous study suggested a significant association of pregnancy-associated plasma protein-A2 (PAPPA2) with DDH susceptibility in Chinese Han population. But with the consideration of the sample size, the association was still debatable. To confirm the association of the reported single nucleotide polymorphism (SNP) in PAPPA2, rs726252 with DDH, we conducted a case-control study in a larger number of subjects. We genotyped rs726252 in 697 DDH subjects and 707 control subjects by TaqMan assay. The association between this SNP and DDH was evaluated statistically. No significant difference was found in any comparison of genotype distribution nor allele frequency between cases and controls. Our replication study indicated that the association between rs726252 and DDH in Chinese Han population was debatable. The association between PAPPA2 and DDH should be evaluated by additional studies.

A SNP in the 5'UTR of GDF5 is associated with susceptibility to symptomatic lumbar disc herniation in the Chinese Han population

PURPOSE

The aim of the present study is to assess whether the single nucleotide polymorphism in the GDF5 (+104T/C; rs143383) is associated with the symptomatic lumbar disc herniation in the Chinese Han population and the identification of the mechanisms of its action.

METHODS

This study consisted of 231 patients with symptomatic lumbar disc herniation as the case group and 370 patients who had a lifetime lack of symptoms as the control group. PCR products were genotyped. Thirty-eight disc specimens derived from the cases were analyzed by immunohistochemical staining. The stain intensity of immunohistochemistry was quantified using a computerized image analysis system.

RESULTS

Significant differences in genotypic and allelic frequencies were found between case group and control group (TT genotype P < 0.001; CC genotype P = 0.002; T allele P < 0.001). The T allele was more frequent in the case group regardless of gender (Female P = 0.018; Male P < 0.001). Significant differences were found in the genotype frequencies when stratified by gender except the comparison between the CC genotype and other genotypes combined among the female samples (P > 0.05). A semi-quantification of collagen protein in the nucleus pulposus showed that the average collagen protein content in TC group was higher than in TT group (P < 0.05).

CONCLUSION

Our results suggested that the GDF5 polymorphism is associated with a susceptibility to symptomatic lumbar disc herniation in the Chinese Han population and type II collagen in the nucleus pulposus may be a key factor in susceptibility to symptomatic lumbar disc herniation.

Advances in osteoarthritis genetics

Osteoarthritis (OA), the most common form of arthritis, is a highly debilitating disease of the joints and can lead to severe pain and disability. There is no cure for OA. Current treatments often fail to alleviate its symptoms leading to an increased demand for joint replacement surgery. Previous epidemiological and genetic research has established that OA is a multifactorial disease with both environmental and genetic components. Over the past 6 years, a candidate gene study and several genome-wide association scans (GWAS) in populations of Asian and European descent have collectively established 15 loci associated with knee or hip OA that have been replicated with genome-wide significance, shedding some light on the aetiogenesis of the disease. All OA associated variants to date are common in frequency and appear to confer moderate to small effect sizes. Some of the associated variants are found within or near genes with clear roles in OA pathogenesis, whereas others point to unsuspected, less characterised pathways. These studies have also provided further evidence in support of the existence of ethnic, sex, and joint specific effects in OA and have highlighted the importance of expanded and more homogeneous phenotype definitions in genetic studies of OA.

Repairing cartilage defects with bone marrow mesenchymal stem cells induced by CDMP and TGF-β1

The aim of this study was to explore the ability for chondrogenic differentiation of bone marrow mesenchymal stems cells (BMSCs) induced by either cartilage-derived morphogenetic protein 1 (CDMP-1) alone or in the presence of transforming growth factor-β1 (TGF-β1) in vivo and in vitro. BMSCs and poly-lactic acid/glycolic acid copolymer (PLGA) scaffold were analyzed for chondrogenic capacity induced by CDMP-1 and TGF-β1 in vivo and in vitro. Chondrogenic differentiation of BMSCs into chondrocytes using a high density pellet culture system was tested, whether they could be maintained in 3-D PLGA scaffold instead of pellet culture remains to be explored. Under the culture of high-density cell suspension and PLGA frame, BMSCs were observed the ability to repair cartilage defects by either CDMP-1 alone or in the presence of TGF-β1 in vitro. Then the cell-scaffold complex was implanted into animals for 4 and 8 weeks for in vivo test. The content of collagen type II and proteoglycan appeared to increase over time in the constructs of the induced groups (CDMP in the presence of TGF-β1), CDMP group and TGF group. However, the construct of the control group did not express them during the whole culture time. At 4 and 8 weeks, the collagen type II expression of the induced group was higher than the sum of TGF group and CDMP group by SSPS17.0 analysis. BMSCs and PLGA complex induced by CDMP-1 and TGF- β1 can repair cartilage defects more effectively than that induced by CDMP-1 or TGF-β1 only.

Rs143383 in the growth differentiation factor 5 (GDF5) gene significantly associated with osteoarthritis (OA)-a comprehensive meta-analysis

Family, twin, adoption studies show osteoarthritis (OA) has a substantial genetic component. Several studies have shown an association between OA and Growth Differentiation Factor 5 (GDF5), some others have not. Thus, the status of the OA-GDF5 association is uncertain. This meta-analysis was applied to case-control studies of the association between OA and GDF5 to assess the joint evidence for the association, the influence of individual studies, and evidence for publication bias. Relevant studies were identified from the following electronic databases: MEDLINE and current contents before Feb. 2012. For the case-control studies, the authors found 1) support for the association between OA and GDF5. The rs143383 polymorphism was significantly associated with OA [fixed: OR and 95% CI: 1.193 (1.139-1.249), p < 0.001; random: OR and 95% CI: 1.204 (1.135-1.276), p < 0.001], 2) no evidence that this association was accounted for by any one study, and 3) no evidence for publication bias. Although the effect size of the association between OA and GDF5 is small, there is suggestive evidence for an association. Further studies are needed to clarify what variant of GDF5 (or some nearby gene) accounts for this association.

Epidemiology of osteoarthritis and associated comorbidities

Osteoarthritis (OA) is the most common cause of walking-related disability among older adults in the United States, and the prevalence and incidence of OA are increasing rapidly. Systemic and local risk factors for knee OA have been identified, and obesity and joint injury appear to be the strongest risk factors that are both modifiable and have the potential for substantial impact on a population level. The risk factors for functional decline and disability in persons with symptomatic OA have been examined in relatively few studies. The course of functional decline in persons with symptomatic OA on a population level is generally one of stable to slowly deteriorating function, but on an individual level, many patients maintain function or improve during the first 3 years of follow-up. Obesity stands out as one of few modifiable risk factors of OA that also is a potentially modifiable predictor of functional decline. Physical activity also appears to have a substantial protective impact on future OA-related disability. Further epidemiologic studies and randomized controlled trials are needed to prioritize prevention through targeting these modifiable risk factors for OA and related disability.

Genetic study on developmental dysplasia of the hip

BACKGROUND

Developmental dysplasia of the hip (DDH) is a developmental disorder of the hip joint that results in an abnormal socket of the femoral head, ranging from instability, subluxation and complete dislocation of the hip joint. DDH has a considerable genetic component.

DESIGN

We reviewed the recent progress on genetic study of DDH.

RESULTS

By linkage and case-control association studies, DDH loci have been identified with several susceptibility genes that involve in bone and joint biology; however, no unequivocal genes with global significance have been detected. The current problem of the association study in DDH is discussed.

CONCLUSIONS

By advanced technologies and international collaboration, we need to find more susceptibility genes and bridge the gap between genetic evidence and molecular mechanisms.

The classification of degenerative hip disease

It is probable that both genetic and environmental factors play some part in the aetiology of most cases of degenerative hip disease. Geneticists have identified some single gene disorders of the hip, but have had difficulty in identifying the genetics of many of the common causes of degenerative hip disease. The heterogeneity of the phenotypes studied is part of the problem. A detailed classification of phenotypes is proposed. This study is based on careful documentation of 2003 consecutive total hip replacements performed by a single surgeon between 1972 and 2000. The concept that developmental problems may initiate degenerative hip disease is supported. The influences of gender, age and body mass index are outlined. Biomechanical explanations for some of the radiological appearances encountered are suggested. The body weight lever, which is larger than the abductor lever, causes the abductor power to be more important than body weight. The possibility that a deficiency in joint lubrication is a cause of degenerative hip disease is discussed. Identifying the phenotypes may help geneticists to identify genes responsible for degenerative hip disease, and eventually lead to a definitive classification.

Etiology of osteoarthritis: genetics and synovial joint development

Osteoarthritis (OA) has a considerable hereditary component and is considered to be a polygenic disease. Data derived from genetic analyses and genome-wide screening of individuals with this disease have revealed a surprising trend: genes associated with OA tend to be related to the process of synovial joint development. Mutations in these genes might directly cause OA. In addition, they could also determine the age at which OA becomes apparent, the joint sites involved, the severity of the disease and how rapidly it progresses. In this Review, I propose that genetic mutations associated with OA can be placed on a continuum. Early-onset OA is caused by mutations in matrix molecules often associated with chondrodysplasias, whereas less destructive structural abnormalities or mutations confer increased susceptibility to injury or malalignment that can result in middle-age onset. Finally, mutations in molecules that regulate subtle aspects of joint development and structure lead to late-onset OA. In this Review, I discuss the genetics of OA in general, but focus on the potential effect of genetic mutations associated with OA on joint structure, the role of joint structure in the development of OA--using hip abnormalities as a model--and how understanding the etiology of the disease could influence treatment.

Association of a single nucleotide polymorphism in pregnancy-associated plasma protein-A2 with developmental dysplasia of the hip: a case-control study

Developmental dysplasia of the hip (DDH), previously known as congenital hip dislocation, is a frequently disabling condition characterized by premature arthritis in later life. Genetic influence on DDH has been long known, but is still poorly understood. Previously, we have performed a genome-wide linkage scan with Affymetrix 10K genechip for a four-generation Chinese family, which included 19 healthy members and five patients with DDH. Parametric and nonparametric multipoint linkage analyses were carried out with Genespring GT v.2.0 software, and the logarithm of odds (LOD) score and nonparametric linkage (NPL) score were calculated. For parametric linkage analysis, an assuming autosomal recessive trait was used with full penetrance, and Affymetrix "Asian" allele frequencies. The NPL score of 2.698 (P=0.0156) and LOD score of 2.119 (θ=0) were obtained on chromosome 1q25.2a for one marker (rs726252). The single nucleotide polymorphism (SNP) rs726252 locates in the region of fifth intron of pregnancy-associated plasma protein-A2 (PAPPA2). Although neither LOD nor NPL scores of rs726252 has exceeded 3.0, several researches have demonstrated that PAPPA2 have important consequences for the development of the fetus and normal postnatal growth. To further evaluate this possible association, in the present study, we examined the genetic association of rs726252 in PAPPA2 gene with sporadic DDH in Han Chinese population using case-control study, including 310 patients with sporadic DDH and 487 control subjects, and found a significant association between PAPPA2 and DDH.

Genetics of osteoarthritis

PURPOSE OF REVIEW

A number of reasonably powered osteoarthritis genome-wide association scans are now in the final phases of their analysis, leaving us all with baited breath. This review highlights some of the osteoarthritis signals and subsequent insights that have emerged from the candidate studies and smaller scale scans that have preceded these more powered studies, and which could therefore be considered as appetizers to the hopeful treats to follow.

RECENT FINDINGS

If one applies the strict criteria of genome-wide significance thresholds, only two current signals pass muster: GDF5 and 7p22. If one relaxes slightly, other signals emerge, such as DIO2, SMAD3 and ASPN. After these, however, we enter the realm where faith takes precedence.

SUMMARY

The search for osteoarthritis susceptibility loci has not been as successful as many had anticipated. This reflects many factors, including the heterogeneous nature of the disease, the tendency to use less severe phenotypes in genetic searches and the reliance on underpowered studies. We do, however, have some successes and in the very near future others will emerge from the more powered scans. Hopefully, combining the current with the new will help our attempts to understand the cause of this complex, common arthritis.

Expression of the osteoarthritis-associated gene GDF5 is modulated epigenetically by DNA methylation

GDF5 is involved in synovial joint development, maintenance and repair, and the rs143383 C/T single nucleotide polymorphism (SNP) located in the 5'UTR of GDF5 is associated, at the genome-wide significance level, with osteoarthritis susceptibility, and with other musculoskeletal phenotypes including height, congenital hip dysplasia and Achilles tendinopathy. There is a significant reduction in the expression of the disease-associated T allele relative to the C allele in synovial joint tissues, an effect influenced by a second SNP (rs143384, C/T) also within the 5'UTR. The differential allelic expression (DAE) imbalance of the C and T alleles of rs143383 varies intra- and inter-individually, suggesting that DAE may be modulated epigenetically. The C alleles of both SNPs form CpG dinucleotides that are potentially amenable to regulation by methylation. Here, we have examined whether DNA methylation regulates GDF5 expression and the allelic imbalance caused by rs143383. We observed methylation of the GDF5 promoter and 5'UTR in cell lines and joint tissues, with demethylation correlating with increased GDF5 expression. The CpG sites created by the C alleles at rs143383 and rs143384 were variably methylated, and treatment of a heterozygous cell line with a demethylating agent further increased the allelic expression imbalance between the C and T alleles. This demonstrates that the genetic effect of the rs143383 SNP on GDF5 expression is modulated epigenetically by DNA methylation. The variability in DAE of rs143383 is therefore partly accounted for by differences in DNA methylation that could influence the penetrance of this allele in susceptibility to common musculoskeletal diseases.

Knee osteoarthritis, lumbar-disc degeneration and developmental dysplasia of the hip--an emerging genetic overlap

Genetics highlights relationships between biological systems, and as the number of defined osteoarthritis susceptibility alleles increases, there is the natural tendency to assess whether the alleles influence other musculoskeletal phenotypes. That has proven to be the case for the GDF5 polymorphism rs143383, a risk factor for knee osteoarthritis and several other common conditions, including lumbar-disc degeneration and developmental dysplasia of the hip. Another interesting example has recently emerged in the repeat polymorphism of the asporin gene, ASPN, which is also associated with these three phenotypes. Such discoveries increase our understanding of shared disease etiology but also emphasize the complexity of common genetic risk.

Deep sequencing of GDF5 reveals the absence of rare variants at this important osteoarthritis susceptibility locus

OBJECTIVE

The common single nucleotide polymorphism (SNP) rs143383 in the 5' untranslated region (5'UTR) of growth and differentiation factor 5 (GDF5) is strongly associated with osteoarthritis (OA) and influences GDF5 allelic expression in vitro and in the joint tissues of OA patients. This effect is modulated in cis by another common SNP, also located within the 5'UTR, whilst a common SNP in the 3'UTR influences allelic expression independent of rs143383. DNA variants can be common, rare or extremely rare/unique. To therefore enhance our understanding of the allelic architecture of this very important OA susceptibility locus we sequenced the gene for potentially functional and novel rare variants.

METHOD

Using the Sanger method we sequenced GDF5 in 992 OA patients and 944 controls, with DNA changes identified by sequencing software. We encompassed the protein-coding region of the two GDF5 exons, both untranslated regions and approximately 100 bp of the proximal promoter of the gene.

RESULTS

We detected 13 variants. Six were extremely rare with minor allele frequencies (MAFs) of ≤ 0.0006. One is in a predicted transcription factor binding site in the GDF5 promoter whilst two substitute conserved amino acids. The remaining seven variants were common and are previously known variants, with MAFs ranging from 0.025 to 0.39. There was a complete absence of variants with frequencies in-between the extremely rare (n=6) and the common (n=7).

CONCLUSIONS

This is the first report of the deep sequencing of an OA susceptibility locus. The absence of rare variants informs us that within the regions of the gene that we have sequenced GDF5 does not harbour any novel variants that are able to contribute, at a population level, to the OA association signal mediated by rs143383 nor does it harbour, at a population level, any novel variants that can influence OA susceptibility independent of rs143383.

Osteoarthritis year 2010 in review: genetics

At the 2010 Osteoarthritis Research Society International (OARSI) congress in Brussels I was asked to present on "Genetics" in the "Year in Review" session. This gave me an opportunity to reflect on the talk that I gave on the same topic at the 2007 OARSI congress in Ft Lauderdale, Florida. My 2007 talk was very upbeat and ended with the hostage to fortune statement "The next few years will provide tremendous clarity in our genetic understanding of osteoarthritis".

Association of the D repeat polymorphism in the ASPN gene with developmental dysplasia of the hip: a case-control study in Han Chinese

Introduction

Developmental dysplasia of the hip (DDH) is a common skeletal disease, which is characterized by abnormal seating of the femoral head in the acetabulum. Genetic factors play a considerable role in the etiology of DDH. Asporin (ASPN) is an ECM protein which can bind to TGF-β1 and sequentially inhibit TGF-β/Smad signaling. A functional aspartic acid (D) repeat polymorphism of ASPN was first described as an osteoarthritis-associated polymorphism. As TGF-β is well known as an important regulator in the development of skeletal components, ASPN may also be involved in the etiology of DDH. Our objective is to evaluate whether the D repeat polymorphism of ASPN is associated with DDH in Han Chinese.

Methods

The D repeat polymorphism was genotyped in 370 DDH patients and 445 control subjects, and the allelic association of the D repeat was examined.

Results

From D11 to D18, eight alleles were identified. D13 allele is the most common allele both in control and DDH groups, the frequencies are 67.3% and 58.1% respectively. In the DDH group, a significantly higher frequency of the D14 allele and significantly lower frequency of D13 was observed. The association of D14 and D13 was found in both females and males after stratification by gender. There was no significant difference in any other alleles we examined.

Conclusions

Our results show an obvious association between the D repeat polymorphism of ASPN and DDH. It indicates that ASPN is an important regulator in the etiology of DDH.