A novel dominant-negative mutation in Gdf5 generated by ENU mutagenesis impairs joint formation and causes osteoarthritis in mice

Sox, Fox, and Lmx1b binding sites differentially regulate a Gdf5-Associated regulatory region during elbow development

Introduction: The articulating ends of limb bones have precise morphology and asymmetry that ensures proper joint function. Growth differentiation factor 5 (Gdf5) is a secreted morphogen involved in cartilage and bone development that contributes to the architecture of developing joints. Dysregulation of Gdf5 results in joint dysmorphogenesis often leading to progressive joint degeneration or osteoarthritis (OA). The transcription factors and cis-regulatory modules (CRMs) that regulate Gdf5 expression are not well characterized. We previously identified a Gdf5-associated regulatory region (GARR) that contains predicted binding sites for Lmx1b, Osr2, Fox, and the Sox transcription factors. These transcription factors are recognized factors involved in joint morphogenesis and skeletal development. Methods: We used in situ hybridization to Gdf5, Col2A1, and the transcription factors of interest in developing chicken limbs to determine potential overlap in expression. We further analyzed scRNA-seq data derived from limbs and knees in published mouse and chicken datasets, identifying cells with coexpression of Gdf5 and the transcription factors of interest. We also performed site-directed mutatgenesis of the predicted transcription factor binding sites in a GARR-reporter construct and determined any change in activity using targeted regional electroporation (TREP) in micromass and embryonic chicken wing bioassays. Results: Gdf5 expression overlapped the expression of these transcription factors during joint development both by in situ hybridization (ISH) and scRNA-seq analyses. Within the GARR CRM, mutation of two binding sites common to Fox and Sox transcripstion factors reduced enhancer activity to background levels in micromass cultures and in ovo embryonic chicken wing bioassays, whereas mutation of two Sox-only binding sites caused a significant increase in activity. These results indicate that the Fox/Sox binding sites are required for activity, while the Sox-only sites are involved in repression of activity. Mutation of Lmx1b binding sites in GARR caused an overall reduction in enhancer activity in vitro and a dorsal reduction in ovo. Despite a recognized role for Osr2 in joint development, disruption of the predicted Osr2 site did not alter GARR activity. Conclusion: Taken together, our data indicates that GARR integrates positive, repressive, and asymmetrical inputs to fine-tune the expression of Gdf5 during elbow joint development.

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.

Current Insights Into the Maintenance of Structure and Function of Intervertebral Disc: A Review of the Regulatory Role of Growth and Differentiation Factor-5

Intervertebral disc degeneration (IDD), characterized by conversion of genotypic and phenotypic, is a major etiology of low back pain and disability. In general, this process starts with alteration of metabolic homeostasis leading to ongoing inflammatory process, extracellular matrix degradation and fibrosis, diminished tissue hydration, and impaired structural and mechanical functionality. During the past decades, extensive studies have focused on elucidating the molecular mechanisms of degeneration and shed light on the protective roles of various factors that may have the ability to halt and even reverse the IDD. Mutations of GDF-5 are associated with several human and animal diseases that are characterized by skeletal deformity such as short digits and short limbs. Growth and differentiation factor-5 (GDF-5) has been shown to be a promise biological therapy for IDD. Substantial literature has revealed that GDF-5 can decelerate the progression of IDD on the molecular, cellular, and organ level by altering prolonged imbalance between anabolism and catabolism. GDF family members are the central signaling moleculars in homeostasis of IVD and upregulation of their gene promotes the expression of healthy nucleus pulposus (NP) cell marker genes. In addition, GDF signaling is able to induce mesenchymal stem cells (MSCs) to differentiate into NPCs and mobilize resident cell populations as chemotactic signals. This review will discuss the promising critical role of GDF-5 in maintenance of structure and function of IVDs, and its therapeutic role in IDD endogenous repair.

Regulatory Mechanisms of Prg4 and Gdf5 Expression in Articular Cartilage and Functions in Osteoarthritis

Owing to the rapid aging of society, the numbers of patients with joint disease continue to increase. Accordingly, a large number of patients require appropriate treatment for osteoarthritis (OA), the most frequent bone and joint disease. Thought to be caused by the degeneration and destruction of articular cartilage following persistent and excessive mechanical stimulation of the joints, OA can significantly impair patient quality of life with symptoms such as knee pain, lower limb muscle weakness, or difficulty walking. Because articular cartilage has a low self-repair ability and an extremely low proliferative capacity, healing of damaged articular cartilage has not been achieved to date. The current pharmaceutical treatment of OA is limited to the slight alleviation of symptoms (e.g., local injection of hyaluronic acid or non-steroidal anti-inflammatory drugs); hence, the development of effective drugs and regenerative therapies for OA is highly desirable. This review article summarizes findings indicating that proteoglycan 4 (Prg4)/lubricin, which is specifically expressed in the superficial zone of articular cartilage and synovium, functions in a protective manner against OA, and covers the transcriptional regulation of Prg4 in articular chondrocytes. We also focused on growth differentiation factor 5 (Gdf5), which is specifically expressed on the surface layer of articular cartilage, particularly in the developmental stage, describing its regulatory mechanisms and functions in joint formation and OA pathogenesis. Because several genetic studies in humans and mice indicate the involvement of these genes in the maintenance of articular cartilage homeostasis and the presentation of OA, molecular targeting of Prg4 and Gdf5 is expected to provide new insights into the aetiology, pathogenesis, and potential treatment of OA.

Establishment of mouse line showing inducible priapism-like phenotypes

Purpose

Penile research is expected to reveal new targets for treatment and prevention of the complex mechanisms of its disorder including erectile dysfunction (ED). Thus, analyses of the molecular processes of penile ED and continuous erection as priapism are essential issues of reproductive medicine.

Methods

By performing mouse N‐ethyl‐N‐nitrosourea mutagenesis and exome sequencing, we established a novel mouse line displaying protruded genitalia phenotype (PGP; priapism‐like phenotype) and identified a novel Pitpna gene mutation for PGP. Extensive histological analyses on the Pitpna mutant and intracavernous pressure measurement (ICP) and liquid chromatography–electrospray ionization tandem mass spectrometry (LC–ESI/MS)/MS analyses were performed.

Results

We evaluated the role of phospholipids during erection for the first time and showed the mutants of inducible phenotypes of priapism. Moreover, quantitative analysis using LC–ESI/MS/MS revealed that the level of phosphatidylinositol (PI) was significantly lower in the mutant penile samples. These results imply that PI may contribute to penile erection by PITPα.

Conclusions

Our findings suggest that the current mutant is a mouse model for priapism and abnormalities in PI signaling pathways through PITPα may lead to priapism providing an attractive novel therapeutic target in its treatment.

Frequency of Growth Differentiation Factor 5 rs143383 and asporin D-repeat polymorphisms in patients with hand and knee osteoarthritis in Kurdistan province, Iran

AIM

Osteoarthritis (OA) is the most common chronic joint disorder, resulting from the breakdown of joint cartilage. It occurs in the knees, hands, and hips, leading to pain, stiffness, inflammation, and swelling.

METHODS

In this study, 100 hand and knee OA patients, meeting the American College of Rheumatology criteria were included in the case group, and 100 healthy individuals were allocated to the control group. Blood samples were collected from the participants. After DNA extraction, genotyping was carried out for GDF5 rs143383 C/T polymorphism by allele-specific polymerase chain reaction (ASPCR) and for D-repeat alleles of asporin (ASPN) by conventional PCR assay.

RESULTS

The results showed that the frequency of the D14 allele of ASPN was significantly higher than other alleles in the case group (P = .0001). Also, the frequency of the D14 allele among women was significantly higher than in men (P = .004). Moreover, the frequency of the TT allele in GDF5 rs143383 C/T polymorphism was significantly higher than the CC and CT alleles in the case group, compared with the control group (P = .001). A significant difference was found between the TT allele and other alleles in female and male patients compared with the control group (P = .02).

CONCLUSIONS

The D14 allele of the ASPN gene and TT allele of the GDF5 gene (rs143383 + 104T/C) are associated with hand and knee OA in the Kurdish population, indicating that these alleles could be risk factors for OA, at least in our populations.

Latent developmental potential to form limb-like skeletal structures in zebrafish

Changes in appendage structure underlie key transitions in vertebrate evolution. Addition of skeletal elements along the proximal-distal axis facilitated critical transformations, including the fin-to-limb transition that permitted generation of diverse modes of locomotion. Here, we identify zebrafish mutants that form supernumerary long bones in their pectoral fins. These new bones integrate into musculature, form joints, and articulate with neighboring elements. This phenotype is caused by activating mutations in previously unrecognized regulators of appendage patterning, vav2 and waslb, that function in a common pathway. This pathway is required for appendage development across vertebrates, and loss of Wasl in mice causes defects similar to those seen in murine Hox mutants. Concordantly, formation of supernumerary bones requires Hox11 function, and mutations in the vav2/wasl pathway drive enhanced expression of hoxa11b, indicating developmental homology with the forearm. Our findings reveal a latent, limb-like pattern ability in fins that is activated by simple genetic perturbation.

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.

Crim1C140S mutant mice reveal the importance of cysteine 140 in the internal region 1 of CRIM1 for its physiological functions

Cysteine-rich transmembrane bone morphogenetic protein regulator 1 (CRIM1) is a type I transmembrane protein involved in the organogenesis of many tissues via its interactions with growth factors including BMP, TGF-β, and VEGF. In this study, we used whole-exome sequencing and linkage analysis to identify a novel Crim1 mutant allele generated by ENU mutagenesis in mice. This allele is a missense mutation that causes a cysteine-to-serine substitution at position 140, and is referred to as Crim1^C140S. In addition to the previously reported phenotypes in Crim1 mutants, Crim1^C140S homozygous mice exhibited several novel phenotypes, including dwarfism, enlarged seminal vesicles, and rectal prolapse. In vitro analyses showed that Crim1^C140S mutation affected the formation of CRIM1 complexes and decreased the amount of the overexpressed CRIM1 proteins in the cell culture supernatants. Cys140 is located in the internal region 1 (IR1) of the N-terminal extracellular region of CRIM1 and resides outside any identified functional domains. Inference of the domain architecture suggested that the Crim1^C140S mutation disturbs an intramolecular disulfide bond in IR1, leading to the protein instability and the functional defects of CRIM1. Crim1^C140S highlights the functional importance of the IR1, and Crim1^C140S mice should serve as a valuable model for investigating the functions of CRIM1 that are unidentified as yet.

A new mouse model of GLUT1 deficiency syndrome exhibits abnormal sleep-wake patterns and alterations of glucose kinetics in the brain

Dysfunction of glucose transporter 1 (GLUT1) proteins causes infantile epilepsy, which is designated as a GLUT1 deficiency syndrome (GLUT1DS; OMIM #606777). Patients with GLUT1DS display varied clinical phenotypes, such as infantile seizures, ataxia, severe mental retardation with learning disabilities, delayed development, hypoglycorrhachia, and other varied symptoms. Glut1^Rgsc200 mutant mice mutagenized with N-ethyl-N-nitrosourea (ENU) carry a missense mutation in the Glut1 gene that results in amino acid substitution at the 324th residue of the GLUT1 protein. In this study, these mutants exhibited various phenotypes, including embryonic lethality of homozygotes, a decreased cerebrospinal-fluid glucose value, deficits in contextual learning, a reduction in body size, seizure-like behavior and abnormal electroencephalogram (EEG) patterns. During EEG recording, the abnormality occurred spontaneously, whereas the seizure-like phenotypes were not observed at the same time. In sleep-wake analysis using EEG recording, heterozygotes exhibited a longer duration of wake times and shorter duration of non-rapid eye movement (NREM) sleep time. The shortened period of NREM sleep and prolonged duration of the wake period may resemble the sleep disturbances commonly observed in patients with GLUT1DS and other epilepsy disorders. Interestingly, an in vivo kinetic analysis of glucose utilization by positron emission tomography with 2-deoxy-2-[fluorine-18]fluoro-D-glucose imaging revealed that glucose transportation was reduced, whereas hexokinase activity and glucose metabolism were enhanced. These results indicate that a Glut1^Rgsc200 mutant is a useful tool for elucidating the molecular mechanisms of GLUT1DS.

This article has an associated First Person interview with the joint first authors of the paper.

Summary: New phenotypes are revealed by a GLUT1 deficiency mutant mouse model carrying a missense mutation in Glut1.

Knock-in human GDF5 proregion L373R mutation as a mouse model for proximal symphalangism

Proximal symphalangism (SYM1) is an autosomal dominant disorder, mainly characterized by bony fusions of the proximal phalanges of the hands and feet. GDF5 and NOG were identified to be responsible for SYM1. We have previously reported on a p.Leu373Arg mutation in the GDF5 proregion present in a Chinese family with SYM1. Here, we investigated the effects of the GDF-L373R mutation. The variant caused proteolysis efficiency of GDF5 increased in ATDC5 cells. The variant also caused upregulation of SMAD1/5/8 phosphorylation and increased expression of target genes SMURF1, along with COL2A1 and SOX9 which are factors associated with chondrosis. Furthermore, we developed a human-relevant SYM1 mouse model by making a Gdf5^L367R (the orthologous position for L373R in humans) knock-in mouse. Gdf5^L367R/+ and Gdf5^L367R/L367R mice displayed stiffness and adhesions across the proximal phalanx joint which were in complete accord with SYM1. It was also confirmed the joint formation and development was abnormal in Gdf5^L367R/+ and Gdf5^L367R/L367R mice, including the failure to develop the primary ossification center and be hypertrophic chondrocytes during embryonic development. This knock-in mouse model offers a tool for assessing the pathogenesis of SYM1 and the function of the GDF5 proregion.

The Good the Bad and the Ugly of Glycosaminoglycans in Tissue Engineering Applications

High sulfation, low cost, and the status of heparin as an already FDA- and EMA- approved product, mean that its inclusion in tissue engineering (TE) strategies is becoming increasingly popular. However, the use of heparin may represent a naïve approach. This is because tissue formation is a highly orchestrated process, involving the temporal expression of numerous growth factors and complex signaling networks. While heparin may enhance the retention and activity of certain growth factors under particular conditions, its binding 'promiscuity' means that it may also inhibit other factors that, for example, play an important role in tissue maintenance and repair. Within this review we focus on articular cartilage, highlighting the complexities and highly regulated processes that are involved in its formation, and the challenges that exist in trying to effectively engineer this tissue. Here we discuss the opportunities that glycosaminoglycans (GAGs) may provide in advancing this important area of regenerative medicine, placing emphasis on the need to move away from the common use of heparin, and instead focus research towards the utility of specific GAG preparations that are able to modulate the activity of growth factors in a more controlled and defined manner, with less off-target effects.

An ENU-induced p.C225S missense mutation in the mouse Tgfb1 gene does not cause Camurati-Engelmann disease-like skeletal phenotypes

Camurati-Engelmann disease (CED) is a rare sclerosing bone disorder in humans with autosomal dominant inheritance. Mutations in the gene (TGFB1) that encodes transforming growth factor-β1 (TGF-β1) are causative for CED. TGF-β1 signaling is enhanced by the CED-causing mutations. In this study, we performed Tgfb1 mutation screening in an ENU-mutagenized mouse genomic DNA library. We identified a missense mutation in which cysteine was substituted by serine at position 225 (p.C225S), that corresponded to the CED-causing mutation (p.C225R). TGF-β1 mutant protein carrying p.C225S was secreted normally into the extracellular space. Reporter gene assays showed that the p.C225S mutants enhanced TGF-β signaling at the same level as p.C225R mutants. We generated p.C225S homozygous mice and confirmed that the mature TGF-β1 levels in the culture supernatants of the calvarial cells from the homozygotes were significantly higher than those from wild-type mice. Although the skull and femur are sclerotic in CED, these phenotypes were not observed in p.C225S homozygous mice. These results suggest that human and mouse bone tissue react differently to TGF-β1. These findings are useful to pharmacological studies using mouse models in developing drugs that will target TGF-β signaling.

Mutant GDF5 enhances ameloblast differentiation via accelerated BMP2-induced Smad1/5/8 phosphorylation

Bone morphogenetic proteins (BMPs) regulate hard tissue formation, including bone and tooth. Growth differentiation factor 5 (GDF5), a known BMP, is expressed in cartilage and regulates chondrogenesis, and mutations have been shown to cause osteoarthritis. Notably, GDF5 is also expressed in periodontal ligament tissue; however, its role during tooth development is unclear. Here, we used cell culture and in vivo analyses to determine the role of GDF5 during tooth development. GDF5 and its associated BMP receptors are expressed at the protein and mRNA levels during postnatal tooth development, particularly at a stage associated with enamel formation. Furthermore, whereas BMP2 was observed to induce evidently the differentiation of enamel-forming ameloblasts, excess GDF5 induce mildly this differentiation. A mouse model harbouring a mutation in GDF5 (W408R) showed enhanced enamel formation in both the incisors and molars, but not in the tooth roots. Overexpression of the W408R GDF5 mutant protein was shown to induce BMP2-mediated mRNA expression of enamel matrix proteins and downstream phosphorylation of Smad1/5/8. These results suggest that mutant GDF5 enhances ameloblast differentiation via accelerated BMP2-signalling.

The Genetic Epidemiological Landscape of Hip and Knee Osteoarthritis: Where Are We Now and Where Are We Going?

Osteoarthritis (OA) is a complex disease that affects the whole joint, with multiple biological and environmental factors contributing to its development. The heritable component for primary OA accounts for ∼50% of susceptibility. So far, candidate gene studies and genome-wide association scans have established 18 OA-associated loci. These findings account for 11% of the heritability, explaining a rather small fraction of the genetic component. To further unravel the genetic architecture of OA, the field needs to facilitate more precise phenotypic definitions, high genome coverage, and large sample metaanalyses, expecting the identification of rare and low frequency variants with potentially higher penetrance, and more accurate methods for calculating phenotype-genotype correlation. Expression analysis, epigenetics, and investigation of interactions can also help clarify the implicated transcriptional regulatory pathways and provide insights into further novel pathogenic OA mechanisms leading to diagnostic biomarker identification and new, more focused therapeutic disease approaches.

Osteoarthritis pathogenesis: a review of molecular mechanisms

Osteoarthritis (OA), the most prevalent chronic joint disease, increases in prevalence with age, and affects majority of individuals over the age of 65 and is a leading musculoskeletal cause of impaired mobility in the elderly. Because the precise molecular mechanisms which are involved in the degradation of cartilage matrix and development of OA are poorly understood and there are currently no effective interventions to decelerate the progression of OA or retard the irreversible degradation of cartilage except for total joint replacement surgery. In this paper, the important molecular mechanisms related to OA pathogenesis will be summarized and new insights into potential molecular targets for the prevention and treatment of OA will be provided.

Bone Morphogenetic Protein (BMP) signaling in development and human diseases

Bone Morphogenetic Proteins (BMPs) are a group of signaling molecules that belongs to the Transforming Growth Factor-β (TGF-β) superfamily of proteins. Initially discovered for their ability to induce bone formation, BMPs are now known to play crucial roles in all organ systems. BMPs are important in embryogenesis and development, and also in maintenance of adult tissue homeostasis. Mouse knockout models of various components of the BMP signaling pathway result in embryonic lethality or marked defects, highlighting the essential functions of BMPs. In this review, we first outline the basic aspects of BMP signaling and then focus on genetically manipulated mouse knockout models that have helped elucidate the role of BMPs in development. A significant portion of this review is devoted to the prominent human pathologies associated with dysregulated BMP signaling.

Toward regeneration of articular cartilage

Articular cartilage is classified as permanent hyaline cartilage and has significant differences in structure, extracelluar matrix components, gene expression profile, and mechanical property from transient hyaline cartilage found in the epiphyseal growth plate. In the process of synovial joint development, articular cartilage originates from the interzone, developing at the edge of the cartilaginous anlagen, and establishes zonal structure over time and supports smooth movement of the synovial joint through life. The cascade actions of key regulators, such as Wnts, GDF5, Erg, and PTHLH, coordinate sequential steps of articular cartilage formation. Articular chondrocytes are restrictedly controlled not to differentiate into a hypertrophic stage by autocrine and paracrine factors and extracellular matrix microenvironment, but retain potential to undergo hypertrophy. The basal calcified zone of articular cartilage is connected with subchondral bone, but not invaded by blood vessels nor replaced by bone, which is highly contrasted with the growth plate. Articular cartilage has limited regenerative capacity, but likely possesses and potentially uses intrinsic stem cell source in the superficial layer, Ranvier's groove, the intra-articular tissues such as synovium and fat pad, and marrow below the subchondral bone. Considering the biological views on articular cartilage, several important points are raised for regeneration of articular cartilage. We should evaluate the nature of regenerated cartilage as permanent hyaline cartilage and not just hyaline cartilage. We should study how a hypertrophic phenotype of transplanted cells can be lastingly suppressed in regenerating tissue. Furthermore, we should develop the methods and reagents to activate recruitment of intrinsic stem/progenitor cells into the damaged site.

Growth differentiation factor-5 promotes brown adipogenesis in systemic energy expenditure

Although growth differentiation factor-5 (GDF5) has been implicated in skeletal development and joint morphogenesis in mammals, little is known about its functionality in adipogenesis and energy homeostasis. Here, we show a critical role of GDF5 in regulating brown adipogenesis for systemic energy expenditure in mice. GDF5 expression was preferentially upregulated in brown adipose tissues from inborn and acquired obesity mice. Transgenic overexpression of GDF5 in adipose tissues led to a lean phenotype and reduced susceptibility to diet-induced obesity through increased systemic energy expenditure. Overexpression of GDF5 facilitated the development of brown fat-like cells, called brite or beige cells, along with the expression of uncoupling protein-1 in inguinal subcutaneous white adipose tissue. In mutant mice harboring the dominant-negative GDF5, marked impairment in energy expenditure and thermogenesis was seen under obesogenic conditions. Recombinant GDF5 promoted brown adipogenesis through the mothers against decapentaplegic homolog (Smad) and peroxisome proliferator-activated receptor-γ coactivator-1α (PGC-1α) pathways after activation of bone morphogenetic protein receptor (BMPR). These results suggest that brown adipogenesis and energy homeostasis are both positively regulated by the GDF5/BMPR/Smad/PGC-1α signaling pathway in adipose tissues. Modulation of these pathways might be an effective therapeutic strategy for obesity and type 2 diabetes.

A GDF5 point mutation strikes twice--causing BDA1 and SYNS2

Growth and Differentiation Factor 5 (GDF5) is a secreted growth factor that belongs to the Bone Morphogenetic Protein (BMP) family and plays a pivotal role during limb development. GDF5 is a susceptibility gene for osteoarthritis (OA) and mutations in GDF5 are associated with a wide variety of skeletal malformations ranging from complex syndromes such as acromesomelic chondrodysplasias to isolated forms of brachydactylies or multiple synostoses syndrome 2 (SYNS2). Here, we report on a family with an autosomal dominant inherited combination of SYNS2 and additional brachydactyly type A1 (BDA1) caused by a single point mutation in GDF5 (p.W414R). Functional studies, including chondrogenesis assays with primary mesenchymal cells, luciferase reporter gene assays and Surface Plasmon Resonance analysis, of the GDF5^W414R variant in comparison to other GDF5 mutations associated with isolated BDA1 (p.R399C) or SYNS2 (p.E491K) revealed a dual pathomechanism characterized by a gain- and loss-of-function at the same time. On the one hand insensitivity to the main GDF5 antagonist NOGGIN (NOG) leads to a GDF5 gain of function and subsequent SYNS2 phenotype. Whereas on the other hand, a reduced signaling activity, specifically via the BMP receptor type IA (BMPR1A), is likely responsible for the BDA1 phenotype. These results demonstrate that one mutation in the overlapping interface of antagonist and receptor binding site in GDF5 can lead to a GDF5 variant with pathophysiological relevance for both, BDA1 and SYNS2 development. Consequently, our study assembles another part of the molecular puzzle of how loss and gain of function mutations in GDF5 affect bone development in hands and feet resulting in specific types of brachydactyly and SYNS2. These novel insights into the biology of GDF5 might also provide further clues on the pathophysiology of OA.

Mutations can be generally classified in loss- or gain-of-function mutations depending on their specific pathomechanism. Here we report on a GDF5 mutation, p.W414R, which is associated with brachydactyly type A1 (BDA1) and Multiple Synostoses Syndrome 2 (SYNS2). Interestingly, whereas shortening of phalangeal elements (brachydactyly) is thought to be caused by a loss of function, bony fusions of joints (synostoses) are due to a gain of function mechanism. Therefore, the question arises as to how p.W414R in GDF5 leads to this combination of phenotypes. In our functional studies, we included two reported GDF5 mutations, which are associated with isolated forms of SYNS2 (GDF5^E491K) or BDA1 (GDF5^R399C), respectively. We demonstrate that an impaired interaction between the extracellular antagonist NOGGIN (NOG) and GDF5 is likely to cause a joint fusion phenotype such as SYNS2. In contrast, GDF5 mutations associated with BDA1 rather exhibit an altered signaling activity through BMPR1A. Consequently, the GDF5^W414R mutation negatively affects both interactions in parallel, which causes the combined phenotype of SYNS2 and BDA1.

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.

Dominant negative mutations of Caenorhabditis elegans daf-7 confer a novel developmental phenotype

BACKGROUND

TGF-β signaling pathways are involved in the control of development in every member of the animal kingdom. As such, TGF-β ligands are widely divergent yet retain a set of core conserved features, specifically, a pre-protein cleavage site and several conserved ligand domain residues, the disruption of which produces a dominant negative phenotype.

RESULTS

We have extended these observations into an invertebrate system by creating a series of loss-of-function Caenorhabditis elegans daf-7 transgenes. When we tested these mutant transgenes in a daf-7/+ background, we saw a molting and excretory canal phenotype. Members of both pathways downstream of daf-4 were required for this phenotype.

CONCLUSIONS

Our results show that the basic mechanisms of TGF-β function are conserved across the animal kingdom. A subset of our daf-7 mutations also produced an unexpected and novel phenotype. Epistasis experiments demonstrated that both daf-3/-5 and sma-4/-9 were downstream of our mutant daf-7 transgenes, which suggests not only a role for DAF-7 in the control of molting and the development of the excretory system but also that daf-7 and dbl-1 signaling may converge downstream of their shared Type II receptor, daf-4. Our approach may unveil new roles in development for other invertebrate TGF-β ligands.

SOX11 contributes to the regulation of GDF5 in joint maintenance

Background

Individual skeletal elements of the vertebrate limbs arise through a segmentation process introducing joints in specific locations. However, the molecular pathways controlling joint formation and subsequent joint maintenance are largely unknown. In this study, we focused on SOX11, and its contribution to the regulation of GDF5, a secreted signal necessary for proper joint formation and postnatal joint homeostasis.

Results

Sox11 is initially expressed broadly in the murine cartilage condensations at early stages of skeletal development, but its expression is specifically increased in the forming joint interzone as is forms. SOX11 overexpression can directly activate GDF5 expression both in vitro and in micromass cell cultures prepared from chick limb buds. Conserved SOX family binding sites are present in the 5’ UTR region of the GDF5 gene and we show SOX11 can specifically bind to one of them. While misexpression of Sox11 in developing chick limbs through RCAS virus infection does not induce Gdf5 expression in ectopic locations, it does enhance its expression. To explore the roles of Sox11 in joint homeostasis, we analyzed adult knee joints in an osteoarthritis mouse model where the medial meniscus and the medial collateral ligament were removed. We also analyzed knee joints from human subjects who underwent total knee replacement surgery. We find that SOX11 is mainly expressed in the weight-bearing areas of knee joints, and its expression is decreased in degraded cartilage during progression of knee osteoarthritis in both mice and humans.

Conclusions

This work implicates SOX11 as a potential regulator of GDF5 expression in joint maintenance and suggests a possible role in the pathogenesis of osteoarthritis.

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.

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.

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.

Behavioral and neuromorphological characterization of a novel Tuba1 mutant mouse

As part of the RIKEN large-scale N-ethyl-N-nitrosourea (ENU) mutagenesis project, we screened mice with a dominant mutation that exhibited abnormal behavior using an open-field test and a home-cage activity test. We tested 495 male progeny of C57BL/6J males treated with ENU and untreated C3H/HeJ females using the open-field test and isolated behavioral mutant M101736, which exhibited a significant increase in spontaneous locomotor activity. We identified a missense mutation in the Tuba1 gene, which encodes the TUBA1 protein, and designated the mutant gene Tuba1(Rgsc1736). This mutation results in an aspartic acid to glycine substitution in the TUBA1 protein. Detailed analyses revealed that Tuba1(Rgsc1736) heterozygotes exhibited inattention to novel objects and aberrant patterns of home-cage activity. The results of a behavioral pharmacological analysis using methylphenidate and morphological analyses of embryonic and adult brains suggested that Tuba1(Rgsc1736) is a novel animal model for neurodevelopmental disorders.

ENU-induced missense mutation in the C-propeptide coding region of Col2a1 creates a mouse model of platyspondylic lethal skeletal dysplasia, Torrance type

The COL2A1 gene encodes the α1(II) chain of the homotrimeric type II collagen, the most abundant protein in cartilage. In humans, COL2A1 mutations create many clinical phenotypes collectively termed type II collagenopathies; however, the genetic basis of the phenotypic diversity is not well elucidated. Therefore, animal models corresponding to multiple type II collagenopathies are required. In this study we identified a novel Col2a1 missense mutation--c.44406A>C (p.D1469A)--produced by large-scale N-ethyl-N-nitrosourea (ENU) mutagenesis in a mouse line. This mutation was located in the C-propeptide coding region of Col2a1 and in the positions corresponding to a human COL2A1 mutation responsible for platyspondylic lethal skeletal dysplasia, Torrance type (PLSD-T). The phenotype was inherited as a semidominant trait. The heterozygotes were mildly but significantly smaller than wild-type mice. The homozygotes exhibited lethal skeletal dysplasias, including extremely short limbs, severe spondylar dysplasia, severe pelvic hypoplasia, and brachydactyly. As expected, these skeletal defects in the homozygotes were similar to those in PLSD-T patients. The secretion of the mutant proteins into the extracellular space was disrupted, accompanied by abnormally expanded rough endoplasmic reticulum (ER) and upregulation of ER stress-related genes, such as Grp94 and Chop, in chondrocytes. These findings suggested that the accumulation of mutant type II collagen in the ER and subsequent induction of ER stress are involved, at least in part in the PLSD-T-like phenotypes of the mutants. This mutant should serve as a good model for studying PLSD-T pathogenesis and the mechanisms that create the great diversity of type II collagenopathies.

Evx1 is required for joint formation in zebrafish fin dermoskeleton

The transcription factor Evx1 is expressed in the joints between individual lepidotrichia (bony ray) segments and at the distal tips of the lepidotrichia in developing zebrafish fins. It is also expressed in the apical growth zone in regenerating fins. However, so far there is no functional evidence that addresses whether Evx1 is required for any aspect of fin development or regeneration. In this study, we use a novel mutation in evx1 to address this. We find that Evx1 is not required for either fin outgrowth or regeneration. All of the fins form normally in evx1 mutants, and there are no significant changes in fin length. In contrast, Evx1 is required for lepidotrichia joint formation during both fin development and regeneration. This is a very specific phenotype as both lepidotrichia hemisegment separations and lepidotrichia bifurcations still form normally in evx1 mutant fins, as do joints in the more proximal endoskeletal radials.

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

OBJECTIVE

Congenital dislocation of the hip (CDH) is a multifactorial disease which involves genetic factors that are still unidentified. Recently, a functional polymorphism (rs143383) of the 5'-untranslated region of GDF5 (Growth/Differentiation Factor 5) - previously reported to be associated with osteoarthritis - has been associated with CDH in a Chinese population. The aim of our study was to determine whether GDF5, known to be involved in bone, joint and cartilage morphogenesis, is also associated with CDH in Caucasians.

DESIGN

We genotyped three tagSNPs (rs224334, rs143384, rs143383) in 239 cases and 239 controls from western Brittany (France) where CDH is frequent, and tested the association using both single-locus and haplotype-based approaches.

RESULTS

The most significant association was observed with rs143384. The T allele of this SNP was overrepresented in cases (65.9% vs 55.9%, P=0.002). Under a recessive model, carriers of the TT genotype had a 1.71-fold higher risk of developing CDH than carriers of the other genotypes (OR(TT vs CT+CC)=1.71, 95% CI: [1.18-2.48], P=0.005). At a nominal level, the association was also significant with rs143383 (OR(TT vs CT+CC)=1.52, 95% CI: [1.05-2.19], P=0.026). The haplotype carrying the susceptibility alleles of these SNPs was also more frequent in cases (65.9% vs 55.9%, OR=1.53, 95% CI: [1.18-1.98], P=0.002).

CONCLUSION

This study reports, for the first time, the association between GDF5 polymorphisms and CDH in Caucasians, and points out another polymorphism of interest that requires further investigation. Reduction in GDF5 expression might lead to developmental deficiency of ligaments and capsule in hip joint, and therefore contribute to CDH pathogenesis.

A recessive screen for genes regulating hematopoietic stem cells

Identification of genes that regulate the development, self-renewal, and differentiation of stem cells is of vital importance for understanding normal organogenesis and cancer; such knowledge also underpins regenerative medicine. Here we demonstrate that chemical mutagenesis of mice combined with advances in hematopoietic stem cell reagents and genome resources can efficiently recover recessive mutations and identify genes essential for generation and proliferation of definitive hematopoietic stem cells and/or their progeny. We used high-throughput fluorescence-activated cell sorter to analyze 9 subsets of blood stem cells, progenitor cells, circulating red cells, and platelets in more than 1300 mouse embryos at embryonic day (E) 14.5. From 45 pedigrees, we recovered 6 strains with defects in definitive hematopoiesis. We demonstrate rapid identification of a novel mutation in the c-Myb transcription factor that results in thrombocythemia and myelofibrosis as proof of principal of the utility of our fluorescence-activated cell sorter-based screen. Such phenotype-driven approaches will provide new knowledge of the genes, protein interactions, and regulatory networks that underpin stem cell biology.

The effect of two point mutations in GDF-5 on ectopic bone formation in a beta-tricalciumphosphate scaffold

The osteoinductivity of human growth-and-differentiation factor-5 (GDF-5) is well established, but a reduced amount of ectopic bone is formed compared to other members of the bone morphogenetic protein (BMP) family like BMP-2. We hypothesized that swap of two BMP-receptor-interacting residues of GDF-5 to amino acids present in BMP-2 (methionine to valine at the sites 453 and 456) may improve the bone formation capacity of the mutant GDF-5. Heterotopic bone formation of a mutant GDF-5 coated beta-TCP carrier was compared to carriers coated with similar amounts (10 microg) of GDF-5 and BMP-2 in SCID mice. Four week explants revealed 6-fold higher ALP activity in the mutant GDF-5 versus the wild type GDF-5 group (p < 0.0001) and 1.4-fold higher levels compared to BMP-2 (p < 0.006). Bone area in histology was significantly higher in mutant GDF-5 versus all other groups at 4 weeks; however, at 8 weeks BMP-2 reached a similar neo-bone formation like mutant GDF-5. Micro-CT evaluation confirmed higher values in the mutant GDF-5 and BMP-2 groups compared to wild type GDF-5. In conclusion, the mutant GDF-5 showed superior bone formation capacity than GDF-5, and a faster induction at similar final outcome as BMP-2. Mutant GDF-5 thus represents a promising new GDF-5 variant for bone regeneration possibly acting via an increased binding affinity to the BMP-type I receptor.

Large-scale analysis of association between GDF5 and FRZB variants and osteoarthritis of the hip, knee, and hand

OBJECTIVE

GDF5 and FRZB have been proposed as genetic loci conferring susceptibility to osteoarthritis (OA); however, the results of several studies investigating the association of OA with the rs143383 polymorphism of the GDF5 gene or the rs7775 and rs288326 polymorphisms of the FRZB gene have been conflicting or inconclusive. To examine these associations, we performed a large-scale meta-analysis of individual-level data.

METHODS

Fourteen teams contributed data on polymorphisms and knee, hip, and hand OA. For rs143383, the total number of cases and controls, respectively, was 5,789 and 7,850 for hip OA, 5,085 and 8,135 for knee OA, and 4,040 and 4,792 for hand OA. For rs7775, the respective sample sizes were 4,352 and 10,843 for hip OA, 3,545 and 6,085 for knee OA, and 4,010 and 5,151 for hand OA, and for rs288326, they were 4,346 and 8,034 for hip OA, 3,595 and 6,106 for knee OA, and 3,982 and 5,152 for hand OA. For each individual study, sex-specific odds ratios (ORs) were calculated for each OA phenotype that had been investigated. The ORs for each phenotype were synthesized using both fixed-effects and random-effects models for allele-based effects, and also for haplotype effects for FRZB.

RESULTS

A significant random-effects summary OR for knee OA was demonstrated for rs143383 (1.15 [95% confidence interval 1.09-1.22]) (P=9.4x10(-7)), with no significant between-study heterogeneity. Estimates of effect sizes for hip and hand OA were similar, but a large between-study heterogeneity was observed, and statistical significance was borderline (for OA of the hip [P=0.016]) or absent (for OA of the hand [P=0.19]). Analyses for FRZB polymorphisms and haplotypes did not reveal any statistically significant signals, except for a borderline association of rs288326 with hip OA (P=0.019).

CONCLUSION

Evidence of an association between the GDF5 rs143383 polymorphism and OA is substantially strong, but the genetic effects are consistent across different populations only for knee OA. Findings of this collaborative analysis do not support the notion that FRZB rs7775 or rs288326 has any sizable genetic effect on OA phenotypes.

The mouse resources at the RIKEN BioResource center

Mice are one of the most important model organisms for studying biological phenomena and diseases processes in life sciences. The biomedical research community has succeeded in launching large scale strategic knockout mouse projects around the world. RIKEN BRC, a comprehensive government funded biological resource center was established in 2001. RIKEN BRC has been acting as the core facility for the mouse resources of the National BioResource Project (NBRP) of the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan since 2002. RIKEN BRC is a founding member of the Federation of International Mouse Resources (FIMRe) together with the Jackson Laboratory, the European Mouse Mutant Archive, and other centers, and has participated in the International Mouse Strain Resource (IMSR) to distribute mouse strains worldwide. With the support of the scientific community, RIKEN BRC has collected over 3,800 strains including inbred, transgenic, knockout, wild-derived, and ENU-induced mutant strains. Excellent mouse models for human diseases and gene functions from academic organizations and private companies are distributed through RIKEN BRC. To meet research and social needs, our mice will be rederived to a specific pathogen-free state, strictly monitored for their health, and accurately tested for their genetic modifications and backgrounds. Users can easily access our mouse resources through the internet and obtain the mouse strains for a minimal fee. Cryopreservation of embryos and sperm is used for efficient preservation of the increasing number of mouse resources. RIKEN BRC collaborates with FIMRe members to support Japanese scientists in the use of valuable mouse resources from around the world.

A novel polymorphism of GDF5 gene and its association with body measurement traits in Bos taurus and Bos indicus breeds

Body measurement traits, influenced by genes and environmental factors, play numerous important roles in the value assessment of productivity and economy. Growth differentiate factor 5 (GDF5), involved in the development and maintenance of bone and cartilage, is an important candidate gene for body measurement traits selection through marker-assisted selection (MAS). In this study, based on the PCR-RFLP technology, we discovered and evaluated the potential association of the single nucleotide polymorphism (SNP) (T586C in exon 1) of the bovine GDF5 gene with body measurement traits in 985 Bos taurus breed, 42 Bos indicus breed and 76 Bos indicus x Bos taurus individuals. As the SNP marker, there were the significant effects on the Body length (BL) in the Bos taurus (BT) and Bos indicus x Bos taurus (BMY) populations (P < 0.05). In BT population, animals with the genotype TT had lower mean values for BL and Hip width (HW) than these with the TC and CC genotype (P < 0.01). In BMY population, animals with the genotype TC had lower mean values for BL than these with the genotype CC (P < 0.05). These results suggest that the SNP of the GDF5 gene could be a very useful genetic marker for body measurement traits in the bovine reproduction and breeding.

A high-speed congenic strategy using first-wave male germ cells

Background

In laboratory mice and rats, congenic breeding is essential for analyzing the genes of interest on specific genetic backgrounds and for analyzing quantitative trait loci. However, in theory it takes about 3–4 years to achieve a strain carrying about 99% of the recipient genome at the tenth backcrossing (N10). Even with marker-assisted selection, the so-called ‘speed congenic strategy’, it takes more than a year at N4 or N5.

Methodology/Principal Findings

Here we describe a new high-speed congenic system using round spermatids retrieved from immature males (22–25 days of age). We applied the technique to three genetically modified strains of mice: transgenic (TG), knockin (KI) and N-ethyl-N-nitrosourea (ENU)-induced mutants. The donor mice had mixed genetic backgrounds of C57BL/6 (B6)∶DBA/2 or B6∶129 strains. At each generation, males used for backcrossing were selected based on polymorphic marker analysis and their round spermatids were injected into B6 strain oocytes. Backcrossing was repeated until N4 or N5. For the TG and ENU-mutant strains, the N5 generation was achieved on days 188 and 190 and the proportion of B6-homozygous loci was 100% (74 markers) and 97.7% (172/176 markers), respectively. For the KI strain, N4 was achieved on day 151, all the 86 markers being B6-homozygous as early as on day 106 at N3. The carrier males at the final generation were all fertile and propagated the modified genes. Thus, three congenic strains were established through rapid generation turnover between 41 and 44 days.

Conclusions/Significance

This new high-speed breeding strategy enables us to produce congenic strains within about half a year. It should provide the fastest protocol for precise definition of the phenotypic effects of genes of interest on desired genetic backgrounds.

ENU mutagenesis, a way forward to understand gene function

Arguably, the main challenge for contemporary genetics is to understand the function of every gene in a mammalian genome. The mouse has emerged as a model for this task because its genome can be manipulated in a number of ways to study gene function or mimic disease states. Two complementary genetic approaches can be used to generate mouse models. A reverse genetics or gene-driven approach (gene to phenotype) starts from a known gene and manipulates the genome to create genetically modified mice, such as knockouts. Alternatively, a forward genetics or phenotype-driven approach (phenotype to gene) involves screening mice for mutant phenotypes without previous knowledge of the genetic basis of the mutation. N-ethyl-N-nitrosourea (ENU) mutagenesis has been widely used for both approaches to generate mouse mutants. Here we review progress in ENU mutagenesis screening, with an emphasis on creating mouse models for human disorders.

Association of a single nucleotide polymorphism in growth differentiate factor 5 with congenital dysplasia of the hip: a case-control study

Introduction

Congenital dysplasia of the hip is an abnormal seating of the femoral head in the acetabulum, mainly caused by shallow acetabulum and lax joint capsule. Genetic factors play a considerable role in the pathogenesis of congenital dysplasia of the hip. The gene growth differentiate factor 5 (GDF5) has been implicated in skeletal development and joint morphogenesis in humans and mice. A functional single nucleotide polymorphism (SNP) in the 5'-untranslated region of GDF5 (rs143383) was reported to be associated with osteoarthritis susceptibility. As a key regulator in morphogenesis of skeletal components and soft tissues in and around the joints, GDF5 may be involved in the aetiology and pathogenesis of congenital dysplasia of the hip. Our objective is to evaluate if the GDF5 SNP is associated with congenital dysplasia of the hip in people of Han Chinese origin.

Methods

The GDF5 SNP was genotyped in 338 children with congenital dysplasia of the hip and 622 control subjects.

Results

The SNP was significantly associated with congenital dysplasia of the hip (p = 0.0037; odds ration (OR) = 1.40; 95% confidence interval (CI) = 1.11 to 1.75). A significant difference was detected in female samples when stratified by gender (p = 0.0053; OR = 1.46; 95% CI = 1.21 to 1.91), and in hip dislocation when stratified by severity (p = 0.0078; OR = 1.43; 95% CI = 1.11 to 1.85).

Conclusions

Our results indicate that GDF5 is important in the aetiology of congenital dysplasia of the hip. To the authors' knowledge this is the first time that a definite association with the congenital dysplasia of the hip susceptibility has been detected.