A missense mutation in the aggrecan C-type lectin domain disrupts extracellular matrix interactions and causes dominant familial osteochondritis dissecans

A rare ACAN non-canonical splicing-site intron variant results in familial short stature

OBJECTIVE

ACAN gene variants, prevalent monogenic defects linked to short stature, are characterized by impaired cartilage generation in growth plates. We aimed to unravel the genetic basis of short stature in a specific pedigree by investigating the role of a novel non-canonical splicing-site variant, c.630-13G > A, within the ACAN gene.

METHOD

Sanger sequencing was used for pedigree verification, and the effects of this variant on mRNA splicing were analyzed through minigene assay.

RESULTS

The study revealed that this variant led to the creation of a previously unreported splice site in the fourth intron, resulting in the incorporation of an 11 bp sequence from the intron into the final transcript. This alteration led to a frameshift and formation of a premature termination codon, impacting the structure of the aggrecan protein.

CONCLUSIONS

We document the pathogenicity of an ACAN non-canonical splicing-site variant, emphasizing the significance of considering intronic variants during genetic testing.

Osteochondritis Dissecans Lesions of the Knee: Evidence-Based Treatment

Osteochondritis dissecans (OCD) of the knee is a potentially disabling condition in adolescent and young adults, which is likely multifactorial in origin. In recent years, there have been notable improvements in identification and treatment. Clinical presentation varies based mostly on OCD lesion stability. Patients with stable lesions generally present with vague knee pain and altered gait while mechanical symptoms and effusion are more common with unstable lesions. Lesions most commonly occur on the lateral aspect of the medial femoral condyle in patients aged 10 to 20 years. Magnetic resonance imaging is vital to diagnose and predict clinical treatment, which is largely based on stability of the fragment. Conservative treatment of stable lesions in patients with open physis is recommended with protected weight-bearing and gradual progression of activities over the course of 3 to 6 months. Stable OCD lesions which failed a nonsurgical course can be treated with transarticular or retrograde drilling while unstable lesions usually require fixation, autologous chondrocyte implantation (ACI), osteochondral autograft transfer (OATS), or osteochondral allograft transplantation. This review highlights the most current understanding of knee OCD lesions and treatment options with the goal of optimizing outcomes in this difficult pathology.

Revision of Failed Osteochondritis dissecans Surgical Treatment: Case Report

BACKGROUND

Osteochondritis dissecans (OD) is one of the most common cartilage lesions of the knee. Conservative treatment is recommended if the lesions are stable with no loose bodies or there are open physes. Surgical intervention is recommended as the primary treatment in symptomatic adults with unstable chondral lesions or with concomitant loose bodies.

METHODS

We describe a case of a patient suffering from OD with a bone lesion in the weight-bearing area of medial femoral condyle. Arthroscopy was performed and an osteochondral fragment from the medial femoral condyle was observed and two articular loose bodies were removed. After months, the patient returned with pain and a locked knee. magnetic resonance imaging (MRI) presented a new unstable chondral flap at the posterior border of the previous lesion. Surgery was performed again, and at open examination, the previous OD lesions were covered by regenerative tissue, with a lesion of 3 cm2 at the inferior medial part of the chondral flap. The peripheral margins were cleaned, and a subchondral crater was curetted. The subchondral lesion was debrided, and the flap was fixed with pins and a central bioresorbable screws.

RESULTS

Revision surgery with fixation of the chondral flap using bioresorbable pins and screws led to satisfactory results.

CONCLUSION

Open revision surgery allowed us a more accurate assessment of the OD area to provide an effective fixation of the chondral flap and in this circumstance, this should have been done after seeing the first MRI.

Regeneration: Bone-Marrow Stimulation of the Talus-Limits and Goals

Bone Marrow Stimulation of osteochondral lesions of the talus has been shown to be a successful way to treat cartilage injuries. Newer data suggest that Bone Marrow Stimulation is best reserved for osteochondral lesions of the talus Sizes Less Than 107.4 mm2 in area. Additionally, newer smaller and deeper techniques to perform bone marrow stimulation have resulted in less subchondral bone damage, less cancellous compaction, and superior bone marrow access with multiple trabecular access channels. Biologic adjuvants such as platelet-rich plasma (PRP), hyaluronic acid (HA), and bone marrow aspirate concentrate (BMAC) may lead to better functional outcomes when used concomitant to bone marrow stimulation.

Bilateral juvenile osteochondrosis dissecans in monozygotic twins: a case report

INTRODUCTION

The etiology of osteochondrosis dissecans (OCD), a chondropathy associated with detachment of the subchondral bone and the overlaying cartilage, is not yet fully understood. While repetitive physical exercise-related stress is usually assumed to be the main risk factor for the occurrence of OCD, genetic predisposition could have an underestimated influence on the development of the disease.

CASE REPORT

We report a case of monozygotic twins with almost identical stages of bilateral osteochondrosis dissecans of the knee joint. In both patients, initially, a unilateral lesion occurred; despite restricted physical exercise, in the further course of the disease a lesion also developed on the contralateral side. While the lesion found most recently demonstrated an ongoing healing process at a 6-month follow-up, the other three lesions showed a natural course of healing under conservative treatment with significant clinical as well as radiological improvements after one year and complete consolidation in magnetic resonance imaging (MRI) after 2 years.

CONCLUSION

There could be a genetic component to the development of OCD, although this has not yet been proven. Based on a two-year MRI follow-up, we were able to show the self-limiting characteristics of juvenile osteochondrosis dissecans.

Genotype and phenotype in patients with ACAN gene variants: Three cases and literature review

OBJECTIVE

To characterize the phenotype spectrum, diagnosis, and response to growth-promoting therapy in patients with ACAN variants causing familial short stature.

METHODS

Three families with ACAN variants causing short stature were reported. Similar cases in the literature were summarized, and the genotype and phenotype were analyzed.

RESULTS

Three novel heterozygous variants, c.757+1G>A, (splicing), c.6229delG, p.(Asp2078Tfs*1), and c.6679C>T, p.(Gln2227*) in the ACAN gene were identified. A total of 314 individuals with heterozygous variants from 105 families and 8 individuals with homozygous variants from 4 families were confirmed to have ACAN variants from literature and our 3 cases. Including our 3 cases, the variants reported comprised 33 frameshift, 39 missense, 23 nonsense, 5 splicing, 4 deletion, and 1 translocation variants. Variation points are scattered throughout the gene, while exons 12, 15, and 10 were most common (25/105, 11/105, and 10/105, respectively). Some identical variants existing in different families could be hot variants, c.532A>T, p.(Asn178Tyr), c.1411C>T, p.(Gln471*), c.1608C>A, p.(Tyr536*), c.2026+1G>A, (splicing), and c.7276G>T, p.(Glu2426*). Short stature, early-onset osteoarthritis, brachydactyly, midfacial hypoplasia, and early growth cessation were the common phenotypic features. The 48 children who received rhGH (and GnRHa) treatment had a significant height improvement compared with before (-2.18 ± 1.06 SD vs. -2.69 ± 0.95 SD, p < 0.001). The heights of children who received rhGH (and GnRHa) treatment were significantly improved compared with those of untreated adults (-2.20 ± 1.10 SD vs. -3.24 ± 1.14 SD, p < 0.001).

CONCLUSION

Our study achieves a new understanding of the phenotypic spectrum, diagnosis, and management of individuals with ACAN variants. No clear genotype-phenotype relationship of patients with ACAN variants was found. Gene sequencing is necessary to diagnose ACAN variants that cause short stature. In general, appropriate rhGH and/or GnRHa therapy can improve the adult height of affected pediatric patients caused by ACAN variants.

Induced Pluripotent Stem Cells in Disease Biology and the Evidence for Their In Vitro Utility

Many human phenotypes are impossible to recapitulate in model organisms or immortalized human cell lines. Induced pluripotent stem cells (iPSCs) offer a way to study disease mechanisms in a variety of differentiated cell types while circumventing ethical and practical issues associated with finite tissue sources and postmortem states. Here, we discuss the broad utility of iPSCs in genetic medicine and describe how they are being used to study musculoskeletal, pulmonary, neurologic, and cardiac phenotypes. We summarize the particular challenges presented by each organ system and describe how iPSC models are being used to address them. Finally, we discuss emerging iPSC-derived organoid models and the potential value that they can bring to studies of human disease.

From "ACAN" to "I CAN": Restoring wellness in a boy with severe osteochondritis dissecans through diagnostic precision combined with optimal medical, surgical and rehabilitation management

Osteochondritis dissecans (OCD) is a disease of the joints characterized by idiopathic focal subchondral lesions. Aggrecan, a proteoglycan encoded by the ACAN gene, is important for cartilage structure and function. We describe the clinical evolution of a patient with short stature, multi-focal OCD, and subchondral osteopenia that appeared linked to a novel pathogenic ACAN variant. A multi-disciplinary approach including medical (bisphosphonate) therapy, surgical intervention and rehabilitation were successful in restoring wellness and physical function.

A Case of Short Stature Caused by a Mutation in the ACAN Gene

Introduction

Aggrecanopathies are rare disorders associated with idiopathic short stature. They are caused by pathogenic changes in the ACAN gene located on chromosome 15q26. In this study, we present a case of short stature caused by mutations in the ACAN gene.

Case Presentation

A 3-year-3-month-old male patient was referred to us because of his short stature. Physical examination revealed proportional short stature, frontal bossing, macrocephaly, midface hypoplasia, ptosis in the right eye, and wide toes. When the patient was 6 years and 3 months old, his bone age was compatible with 7 years of age. The patient underwent clinical exome sequencing and a heterozygous nonsense c.1243G>T, p.(Glu415*) pathogenic variant was detected in the ACAN gene. The same variant was found in his phenotypically similar father. Our patient is the second case with ptosis.

Discussion

ACAN gene mutation should be considered in the differential diagnosis of patients with idiopathic short stature. The development and widespread use of next-generation sequencing technology has increased the diagnostic and treatment possibilities.

Osteochondritis dissecans of the knee: Epidemiology, etiology, and natural history

Osteochondritis dissecans of the knee is a disease that typically affects skeletally immature patients. Clinically manifested with knee pain, limping, and joint disfunction, this condition has remained misunderstood and undervalued for a long period. Although being a rare condition, its awareness is of utmost clinical interest because of the possible severe consequences it can bring when misrecognized or inadequately treated. Its etiology remains unclear and is still debated. Many theories have been proposed, including inflammation, local ischemia, subchondral ossification abnormalities, genetic factors, and repetitive mechanical microtrauma, with a likely interplay of the same. This review article aims to deliver and discuss current and up-to-date concepts on epidemiology, etiology, and natural history of this pediatric condition. Level of evidence: level V.

Knee osteochondritis dissecans-treatment technical aspects

Purpose and objective

Current treatments of different stages of knee osteochondritis Dissecans (OCD) are depending on the age of the patients and the stability of the diseased osteochondral area. The purpose of this paper was to summarize the treatment alternatives in order to simplify the choice for the treating surgeon.

Background and principle results

Osteochondritis dissecans (OCD) of the knee is an idiopathic and local osteochondral abnormality that affects mainly children and adolescents with risk of loosening of osteochondral fragments. A good clinical result can be expected when the physes are still open, when the osteochondritis is small and when the osteochondritis can be assessed as stable by MRI. Unstable OCD lesions most often need to be treated operatively by different fixation methods and when the osteochondral cannot be refixated, different local chondral and osteochondral repairs are available to fill up the defect area to congruity.

Summary and major conclusions

The final choice of which treatment to use is depending on fragment viability and forms. Viable fragments are refixated while poor quality fragments are removed followed by a local biological osteochondral repair. Such osteochondral resurfacing may be single bone marrow stimulation with or without scaffold augmentation or different cell seeded grafts.

The Spectrum of ACAN Gene Mutations in a Selected Chinese Cohort of Short Stature: Genotype-Phenotype Correlation

Objective: Mutations in the ACAN gene have been reported to cause short stature. However, the prevalence estimates of pathogenic ACAN variants in individuals with short stature vary, and the correlation between ACAN genotype and clinical phenotype remain to be evaluated. To determine the prevalence of ACAN variants among Chinese people with short stature and analyze the relationship between genotype and main clinical manifestations of short stature and advanced bone age among patients with ACAN variants.

Methods: We performed next-generation sequencing-based genetic analyses on 442 individuals with short stature. ACAN variants were summarized, previously reported cases were retrospectively analyzed, and an association analysis between genotype and phenotype was conducted.

Result: We identified 15 novel and two recurrent ACAN gene variants in 16 different pedigrees that included index patients with short stature. Among the patients with ACAN variants, 12 of 18 had advanced bone age and 7 of 18 received growth hormone therapy, 5 (71.4%) of whom exhibited variable levels of height standard deviation score improvement. Further analysis showed that patients with ACAN truncating variants had shorter height standard deviation scores (p = 0.0001) and larger bone age–chronological age values (p = 0.0464). Moreover, patients in this Asian population had a smaller mean bone age–chronological age value than those that have been determined in European and American populations (p = 0.0033).

Conclusion: Our data suggest that ACAN mutation is a common cause of short stature in China, especially among patients with a family history of short stature but also among those who were born short for their gestational age without a family history. Patients with truncating variants were shorter in height and had more obvious advanced bone age, and the proportion of patients with advanced bone age was lower in this Asian population than in Europe and America.

Identification of variants in ACAN and PAPSS2 leading to spondyloepi(meta)physeal dysplasias in four Chinese families

Background

Spondyloepi(meta)physeal dysplasias (SE[M]D) are a group of inherited skeletal disorders that mainly affect bone and cartilage, and next‐generation sequencing has aided the detection of genetic defects of such diseases. In this study, we aimed to identify causative variants in four Chinese families associated with SE(M)D.

Methods

We recruited four unrelated Chinese families all displaying short stature and growth retardation. Clinical manifestations and X‐ray imaging were recorded for all patients. Candidate variants were identified by whole‐exome sequencing (WES) and verified by Sanger sequencing. Pathogenicity was assessed by conservation analysis, 3D protein modeling and in silico prediction, and was confirmed according to American College of Medical Genetics and Genomics.

Results

Three novel SE(M)D‐related variants c.1090dupG, c.7168 T > G, and c.2947G > C in ACAN, and one reported variant c.712C > T in PAPSS2 were identified. Among them, c.1090dupG in ACAN and c.712C > T in PAPSS2 caused truncated protein and the other two variants led to amino acid alterations. Conservation analysis revealed sites of the two missense variants were highly conserved, and bioinformatic findings confirmed their pathogenicity. 3D modeling of mutant protein encoded by c.7168 T > G(p.Trp2390Gly) in ACAN proved the structural alteration in protein level.

Conclusion

Our data suggested ACAN is a common pathogenic gene of SE(M)D. This study enriched the genetic background of skeletal dysplasias, and expanded the mutation spectra of ACAN and PAPSS2.

Roles of Chondroitin Sulfate Proteoglycans as Regulators of Skeletal Development

The extracellular matrix (ECM) is critically important for most cellular processes including differentiation, morphogenesis, growth, survival and regeneration. The interplay between cells and the ECM often involves bidirectional signaling between ECM components and small molecules, i.e., growth factors, morphogens, hormones, etc., that regulate critical life processes. The ECM provides biochemical and contextual information by binding, storing, and releasing the bioactive signaling molecules, and/or mechanical information that signals from the cell membrane integrins through the cytoskeleton to the nucleus, thereby influencing cell phenotypes. Using these dynamic, reciprocal processes, cells can also remodel and reshape the ECM by degrading and re-assembling it, thereby sculpting their environments. In this review, we summarize the role of chondroitin sulfate proteoglycans as regulators of cell and tissue development using the skeletal growth plate model, with an emphasis on use of naturally occurring, or created mutants to decipher the role of proteoglycan components in signaling paradigms.

Aggrecan and versican: two brothers close or apart

Aggrecan (Acan) and versican (Vcan) are large chondroitin sulfate proteoglycans of the extracellular matrix. They share the same structural domains at both N and C-termini. The N-terminal G1 domain binds hyaluronan (HA), forms an HA-rich matrix, and regulates HA-mediated signaling. The C-terminal G3 domain binds other extracellular matrix molecules and forms a supramolecular structure that stores TGFb and BMPs and regulates their signaling. EGF-like motifs in the G3 domain may directly act like an EGF ligand. Both Acan and Vcan are present in cartilage, intervertebral disc, brain, heart, and aorta. Their localizations are essentially reciprocal. This review describes their structural domains, expression patterns and functions, and regulation of their expression.

Short stature associated with a novel mutation in the aggrecan gene: A case report and literature review

BACKGROUND

Mutations in the aggrecan (ACAN) gene are identified in patients with: spondyloepiphyseal dysplasia, Kimberley type; short stature with advanced bone age (BA); in the presence or absence of heterozygous ACAN mutation-induced early-onset osteoarthritis and/or osteochondritis dissecans; and spondyloepimetaphyseal dysplasia, ACAN type. Heterozygous mutations contribute to spondyloepiphyseal dysplasia, Kimberley type (MIM#608361), which is a milder skeletal dysplasia. In contrast, homozygous mutations cause a critical skeletal dysplasia, which is called spondyloepimetaphyseal dysplasia, ACAN type (MIM#612813). Lately, investigations on exome and genome sequencing have shown that ACAN mutations can also lead to idiopathic short stature with or without an advanced BA, in the presence or absence of early-onset osteoarthritis and/or osteochondritis dissecans (MIM#165800). We herein reported a heterozygous defect of ACAN in a family with autosomal dominant short stature, BA acceleration, and premature growth cessation.

CASE SUMMARY

A 2-year-old male patient visited us due to growth retardation. The patient presented symmetrical short stature (height 79 cm, < -2 SD) without facial features and other congenital abnormalities. Whole-exome sequencing revealed a heterozygous pathogenic variant c. 871C>T (p. Gln291*) of ACAN, which was not yet reported in cases of short stature. This mutation was also detected in his father and paternal grandmother. According to the Human Gene Mutation Database, 67 ACAN mutations are registered. Most of these mutations are genetically inheritable, and very few children with short stature are associated with ACAN mutations. To date, heterozygous ACAN mutations have been reported in approximately 40 families worldwide, including a few individuals with a decelerated BA.

CONCLUSION

Heterozygous c. 871C>T (p. Gln291*) variation of the ACAN gene was the disease-causing variant in this family. Collectively, our newly discovered mutation expanded the spectrum of ACAN gene mutations.

Novel missense ACAN gene variants linked to familial osteochondritis dissecans cluster in the C-terminal globular domain of aggrecan

The cartilage aggrecan proteoglycan is crucial for both skeletal growth and articular cartilage function. A number of aggrecan (ACAN) gene variants have been linked to skeletal disorders, ranging from short stature to severe chondrodyplasias. Osteochondritis dissecans is a disorder where articular cartilage and subchondral bone fragments come loose from the articular surface. We previously reported a missense ACAN variant linked to familial osteochondritis dissecans, with short stature and early onset osteoarthritis, and now describe three novel ACAN gene variants from additional families with this disorder. Like the previously described variant, these are autosomal dominant missense variants, resulting in single amino acid residue substitutions in the C-type lectin repeat of the aggrecan G3 domain. Functional studies showed that neither recombinant variant proteins, nor full-length variant aggrecan proteoglycan from heterozygous patient cartilage, were secreted to the same level as wild-type aggrecan. The variant proteins also showed decreased binding to known cartilage extracellular matrix ligands. Mapping these and other ACAN variants linked to hereditary skeletal disorders showed a clustering of osteochondritis dissecans-linked variants to the G3 domain. Taken together, this supports a link between missense ACAN variants affecting the aggrecan G3 domain and hereditary osteochondritis dissecans.

Clinical phenotype and musculoskeletal characteristics of patients with aggrecan deficiency

Aggrecan is a proteoglycan within the physeal and articular cartilage. Aggrecan deficiency, due to heterozygous mutations in the ACAN gene, causes dominantly inherited short stature and, in many patients, early-onset osteoarthritis and degenerative disc disease. We aimed to further characterize this phenotypic spectrum with an emphasis on musculoskeletal health. Twenty-two individuals from nine families were enrolled. Histories and examinations focused on joint health, gait analysis, joint specific patient reported outcomes, and imaging studies were performed. All patients had dominantly inherited short stature, with the exception of a de novo mutation. Short stature was worse in adults versus children (median height -3.05 SD vs. -2.25 SD). ACAN mutations were not always associated with bone age advancement (median advancement +1.1 years, range 0 to +2 years). Children had subtle disproportionality and clinically silent joint disease-25% with osteochondritis dissecans (OD). Adults had a high prevalence of joint symptomatology-decline in knee function, disability from spinal complaints, and lower physical activity on outcome measures. Osteoarthritis (OA) and OD was detected in 90% of adults, and orthopedic surgeries were reported in 60%. Aggrecan deficiency leads to short stature with progressive decline in height SD, mild skeletal dysplasia, and increasing prevalence of joint pathology over time. Optimal musculoskeletal health and quality of life can be attained with timely identification of pathology and intervention.

Description of the molecular and phenotypic spectrum in Chinese patients with aggrecan deficiency: Novel ACAN heterozygous variants in eight Chinese children and a review of the literature

OBJECTIVE

This study analyzed eight Chinese short stature children with aggrecan deficiency, and aimed to investigate potential genotype-phenotype correlations, differences in clinical characteristics between the Chinese and the Western populations, and effectiveness of recombinant human growth hormone therapy in patients with ACAN variants through a review of the literature.

METHODS

Pediatric short stature patients with ACAN heterozygous variants were identified using whole-exome sequencing. Subsequently, a literature review was carried out to summarize the clinical features, genetic findings, and efficacy of growth-promoting therapy in patients with ACAN variants.

RESULTS

We identified seven novel ACAN mutations and one recurrent variant. Patients in our center manifested with short stature (average height SDS: -3.30 ± 0.85) with slight dysmorphic characteristics. The prevalence of dysmorphic features in the Chinese populations is significantly lower than that in the Western populations. Meanwhile, only 24.24% of aggrecan-deficient Chinese children showed significantly advanced bone age (BA). Promising therapeutic benefits were seen in the patients who received growth-promoting treatment, with an increase in growth velocity from 4.52 ± 1.00 cm/year to 8.03 ± 1.16 cm/year.

CONCLUSION

This study further expanded the variation spectrum of the ACAN gene and demonstrated that Chinese children with short stature who carried ACAN heterozygous variants exhibited early growth cessation, which may remain unnoticed by clinicians as most of these children had very mild dysmorphic characteristics and showed BA that was consistent with the chronological age. Genetic testing may help in the diagnosis.

Variable expressivity in a family with an aggrecanopathy

Background

Osteochondritis dissecans is a condition wherein there is a subchondral bone lesion that causes pain, inflammation, and cartilage damage. Dominant Familial Osteochondritis Dissecans is a rare and severe form of osteochondritis dissecans (OCD). It is caused by heterozygous pathogenic variants in the gene encoding Aggrecan; ACAN. Aggrecan, a proteoglycan, is an essential component of the articular and growth plate cartilage.

Methods

Herein, we report three individuals from one family; the proband who presented with short stature, a lower limb bone exostosis, and bilateral knee and elbow OCD at the age of 13 years old. His twin brother presented with isolated short stature and his father with short stature and lumbar disc herniation.

Results

Next‐generation sequencing of the ACAN gene in the proband identified a frameshift variant which is also present in the brother and father with short stature. The proband was treated surgically with bilateral elbow microfracture, after the failure of conservative therapy.

Conclusion

To the best of our knowledge, this is the first patient with an aggrecanopathy who presents with osteochondritis dissecans due to a frameshift variant. This family presents with variable expressivity which might be attributed to modifier genes.

Altered Expression of Aggrecan, FAM20B, B3GALT6, and EXTL2 in Patients with Osteoarthritis and Kashin-Beck Disease

OBJECTIVE

The objective of this study was to investigate the expression of enzymes involved in synthesis and modification of chondroitin sulfate (CS) in knee cartilage tissue of patients with osteoarthritis (OA) and Kashin-Beck disease (KBD).

METHODS

The knee articular cartilage samples were obtained from 18 age- and gender-matched donors with 6 each in KBD, OA, and control groups. Hematoxylin and eosin (HE) staining, toluidine blue (TB) staining, and immunohistochemical (IHC) staining were performed to estimate the expression level and localization of aggrecan, along with FAM20B, GalT-II, and EXTL2, which are associated with CS synthesis and modification. Rank-based analyses of variance test was used for the multiple comparisons of discrepancy in the positive staining rate among the 3 groups.

RESULTS

In HE and TB staining results, damaged morphology, decreased chondrocyte numbers and proteoglycans were observed in OA and KBD groups compared with the control group. In line with these trends, the positive staining rates of aggrecan were lower in KBD and OA groups than in the control group. Meanwhile, the positive staining rates of CS chain modifying enzymes FAM20B, GalT-II, and EXTL2 decreased in OA and KBD groups.

CONCLUSIONS

In conclusion, it was demonstrated that altered expression of CS chain modifying enzymes in OA and KBD groups influenced the synthesis procession of CS and could contribute to the damage of cartilage. Further investigation of these enzymes can provide new theoretical and experimental targets for OA and KBD pathogenesis studies.

Chondral and Osteochondritis Dissecans Lesions Treated by Autologous Chondrocytes Implantation: A Mid- to Long-Term Nonrandomized Comparison

OBJECTIVE

The aim of this study was to compare the clinical outcome of cartilage repair with autologous chondrocyte implantation (ACI) in patients with osteochondritis dissecans (OCD) lesions and full-thickness cartilage lesions.

DESIGN

This study included a cohort of 115 consecutive patients with a cartilage lesion of the knee treated with ACI. Of the patients, 35 had an OCD lesion and 80 a full-thickness cartilage lesion. During a follow-up period from 2 to 13 years all treatment failures were identified. The failure rate between OCD lesions and full-thickness cartilage lesions was compared with Kaplan-Meier analysis. Patient-reported outcome was evaluated 2 years postoperatively with the Lysholm score.

RESULTS

During the follow-up 21 out of 115 patients encountered a treatment failure. The failure rate for full-thickness cartilage lesions was 19.1% and for OCD lesions 43.3% over the 10-year follow-up. Patient-reported outcome improved from baseline to 2 years postoperatively. The improvement from baseline was statistically significant, and the Lysholm score improved more than the minimal clinically important difference. The patient-reported outcome showed no difference between lesion types at 2 years.

CONCLUSIONS

In the presented retrospective study, the failure rate of first-generation ACI was higher in OCD lesions than in large full-thickness cartilage lesions, suggesting that OCD lesions may associate with properties that affect the durability of repair tissue. Future prospective studies are needed to tell us how to best repair OCD lesions with biological tissue engineering.

Proteoglycans and Diseases of Soft Tissues

Proteoglycans consist of protein cores to which at least one glycosaminoglycan chain is attached. They play important roles in the physiology and biomechanical function of tendons, ligaments, cardiovascular system, and other systems through their involvement in regulation of assembly and maintenance of extracellular matrix, and through their participation in cell proliferation together with growth factors. They can be divided into two main groups, small and large proteoglycans. The small proteoglycans are also known as small leucine-rich proteoglycans (SLRPs) which are encoded by 18 genes and are further subclassified into Classes I-V. Several members of Class I and II, such as decorin and biglycan from Class I, and Class II fibromodulin and lumican, are known to regulate collagen fibrillogenesis. Decorin limits the diameter of collagen fibrils during fibrillogenesis. The function of biglycan in fibrillogenesis is similar to that of decorin. Though biomechanical function of tendon is compromised in decorin-deficient mice, decorin can substitute for lack of biglycan in biglycan-deficient mice. New data also indicate an important role for biglycan in disorders of the cardiovascular system, including aortic valve stenosis and aortic dissection. Two members of the Class II of SLRPs, fibromodulin and lumican bind to the same site within the collagen molecule and can substitute for each other in fibromodulin- or lumican-deficient mice.Aggrecan and versican are the major representatives of the large proteoglycans. Though they are mainly found in the cartilage where they provide resilience and toughness, they are present also in tensile portions of tendons and, in slightly different biochemical form in fibrocartilage. Degradation by aggrecanase is responsible for the appearance of different forms of aggrecan and versican in different parts of the tendon where these cleaved forms play different roles. In addition, they are important components of the ventricularis of cardiac valves. Mutations in the gene for versican or in the gene for elastin (which binds to versican ) lead to severe disruptions of normal developmental of the heart at least in mice.

Identification of novel ACAN mutations in two Chinese families and genotype-phenotype correlation in patients with 74 pathogenic ACAN variations

Background

ACAN (OMIM 155760) is located on chromosome 15q26 and encodes the production of aggrecan. Aggrecan is a large chondroitin sulfate proteoglycan with a molecular weight of 254 kDa and contains 2530 amino acids. It is a critical structural component of the extracellular matrix of cartilage, including growth plate, articular, and intervertebral disk cartilage. It plays a key role in bone development.

Methods

Here, we describe two pedigrees with loss‐of‐function variants in ACAN. Whole exome sequencing was performed for the probands from each family. We illustrate the clinical variability associated with ACAN variants.

Results

The proband of pedigree A manifested short stature, relative macrocephaly, mild flat nasal bridge, low‐set ears, short neck, and short thumbs. The proband of pedigree B had short height, abnormal vertebral development, and central precocious puberty. By trio‐based whole exome sequencing and in silico analyses, we identified two de novo heterozygous variants of ACAN: NM_013227.4: c.116dupT, p.Arg40Glufs*51 and NM_013227.4: c.2367delC, p.Ser790Glnfs*20 (accession number: AC103982.10).

Conclusion

The clinical manifestations of ACAN gene variants are diverse. ACAN gene variants are important genetic factors for short stature and should be considered as the differential diagnosis of children with idiopathic short stature (ISS).

Congenital Disorders of Deficiency in Glycosaminoglycan Biosynthesis

Glycosaminoglycans (GAGs) including chondroitin sulfate, dermatan sulfate, and heparan sulfate are covalently attached to specific core proteins to form proteoglycans, which are distributed at the cell surface as well as in the extracellular matrix. Proteoglycans and GAGs have been demonstrated to exhibit a variety of physiological functions such as construction of the extracellular matrix, tissue development, and cell signaling through interactions with extracellular matrix components, morphogens, cytokines, and growth factors. Not only connective tissue disorders including skeletal dysplasia, chondrodysplasia, multiple exostoses, and Ehlers-Danlos syndrome, but also heart and kidney defects, immune deficiencies, and neurological abnormalities have been shown to be caused by defects in GAGs as well as core proteins of proteoglycans. These findings indicate that GAGs and proteoglycans are essential for human development in major organs. The glycobiological aspects of congenital disorders caused by defects in GAG-biosynthetic enzymes including specific glysocyltransferases, epimerases, and sulfotransferases, in addition to core proteins of proteoglycans will be comprehensively discussed based on the literature to date.

Retrospective Diagnosis of a Novel ACAN Pathogenic Variant in a Family With Short Stature: A Case Report and Review of the Literature

Short stature is a frequent disorder in the pediatric population and can be caused by multiple factors. In the last few years, the introduction of Next Generation Sequencing (NGS) in the molecular diagnostic workflow led to the discovery of mutations in novel genes causing short stature including heterozygous mutations in ACAN gene. It encodes for aggrecan, a primary proteoglycan component specific for the structure of the cartilage growth plate, articular and intervertebral disc. We report a novel ACAN heterozygous pathogenic variant in a family with idiopathic short stature, early-onset osteoarthritis and osteoarthritis dissecans (SSOAOD). We also performed a literature review summarizing the clinical characteristic of ACAN's patients. The probands are two Caucasian sisters with a family history of short stature and osteoarthritis dissecans. They showed dysmorphic features such as mild midface hypoplasia, brachydactyly and broad thumbs, especially the great toes. The same phenotype was presented in the mother who had had short stature and suffered from intervertebral disc disease. DNA sequencing identified a heterozygous pathogenic variation (c.4390delG p.Val1464Ter) in the sisters, with a maternal inheritance. The nonsense mutation, located on exon 12, results in premature truncation and presumed loss of protein function. In terms of treatment, our patients underwent recombinant human growth hormone replacement therapy, associated with gonadotropin releasing hormone therapy, in order to block early growth cessation and therefore reach a better final height. Our case suggests that SSOAOD ACAN related should be considered in the differential diagnosis of children with autosomal dominant short stature and family history of joints disease.

A wide range of protective and predisposing variants in aggrecan influence the susceptibility for otosclerosis

In this study, we investigated the association of ACAN variants with otosclerosis, a frequent cause of hearing loss among young adults. We sequenced the coding, 5'-UTR and 3'-UTR regions of ACAN in 1497 unrelated otosclerosis cases and 1437 matched controls from six different subpopulations. The association between variants in ACAN and the disease risk was tested through single variant and gene-based association tests. After correction for multiple testing, 14 variants were significantly associated with otosclerosis, ten of which represented independent association signals. Eight variants showed a consistent association across all subpopulations. Allelic odds ratios of the variants identified four predisposing and ten protective variants. Gene-based tests showed an association of very rare variants in the 3'-UTR with the phenotype. The associated exonic variants are all located in the CS domain of ACAN and include both protective and predisposing variants with a broad spectrum of effect sizes and population frequencies. This includes variants with strong effect size and low frequency, typical for monogenic diseases, to low effect size variants with high frequency, characteristic for common complex traits. This single-gene allelic spectrum with both protective and predisposing alleles is unique in the field of complex diseases. In conclusion, these findings are a significant advancement to the understanding of the etiology of otosclerosis.

Germline Saturation Mutagenesis Induces Skeletal Phenotypes in Mice

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

Osteochondritis Dissecans: Current Understanding of Epidemiology, Etiology, Management, and Outcomes

➤

Osteochondritis dissecans occurs most frequently in the active pediatric and young adult populations, commonly affecting the knee, elbow, or ankle, and may lead to premature osteoarthritis.

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While generally considered an idiopathic phenomenon, various etiopathogenetic theories are being investigated, including local ischemia, aberrant endochondral ossification of the secondary subarticular physis, repetitive microtrauma, and genetic predisposition.

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Diagnosis is based on the history, physical examination, radiography, and advanced imaging, with elbow ultrasonography and novel magnetic resonance imaging protocols potentially enabling early detection and in-depth staging.

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Treatment largely depends on skeletal maturity and lesion stability, defined by the presence or absence of articular cartilage fracture and subchondral bone separation, as determined by imaging and arthroscopy, and is typically nonoperative for stable lesions in skeletally immature patients and operative for those who have had failure of conservative management or have unstable lesions.

➤

Clinical practice guidelines have been limited by a paucity of high-level evidence, but a multicenter effort is ongoing to develop accurate and reliable classification systems and multimodal decision-making algorithms with prognostic value.

A High Proportion of Novel ACAN Mutations and Their Prevalence in a Large Cohort of Chinese Short Stature Children

CONTEXT

Aggrecan, encoded by the ACAN gene, is the main proteoglycan component in the extracellular cartilage matrix. Heterozygous mutations in ACAN have been reported to cause idiopathic short stature. However, the prevalence of ACAN pathogenic variants in Chinese short stature patients and clinical phenotypes remain to be evaluated.

OBJECTIVE

We sought to determine the prevalence of ACAN pathogenic variants among Chinese short stature children and characterize the phenotypic spectrum and their responses to growth hormone therapies.

PATIENTS AND METHODS

Over 1000 unrelated short stature patients ascertained across China were genetically evaluated by next-generation sequencing-based test.

RESULT

We identified 10 novel likely pathogenic variants and 2 recurrent pathogenic variants in this cohort. None of ACAN mutation carriers exhibited significant dysmorphic features or skeletal abnormities. The prevalence of ACAN defect is estimated to be 1.2% in the whole cohort; it increased to 14.3% among those with advanced bone age and to 35.7% among those with both advanced bone age and family history of short stature. Nonetheless, 5 of 11 ACAN mutation carries had no advanced bone age. Two individuals received growth hormone therapy with variable levels of height SD score improvement.

CONCLUSION

Our data suggest that ACAN mutation is 1 of the common causes of Chinese pediatric short stature. Although it has a higher detection rate among short stature patients with advanced bone age and family history, part of affected probands presented with delayed bone age in Chinese short stature population. The growth hormone treatment was moderately effective for both individuals.

The Link between Aggrecan and Familial Osteochondritis Dissecans

Osteochondritis dissecans (OCD) is a chronic disease of the articular cartilage characterized by focal lesions of subchondral bone and overlaying cartilage. Through the growing number of reports describing the high prevalence of OCD in some families, the subcategory termed familial OCD (FOCD) was established. With the development of genetic approaches such as genome-wide association studies and sequencing, aggrecan (ACAN) has been identified as one of the genes of interest associated with FOCD. Aggrecan is a crucial protein for the preservation and function of cartilage. However, due to FOCD being characterized relatively recently, there is a paucity of literature on the subject. The purpose of this review is to explore the relationship between ACAN mutations and familial OCD as well as to explore current treatment options and avenues for future research. In vitro and animal studies have shown the importance of ACAN in the preservation of cartilage. However, the only human ACAN mutation related to OCD ever identified is a V2303M mutation in the G3 domain. Multiple treatments have been superficially explored, and some options such as growth hormone (GH) and gonadotrophin-releasing hormone agonists (GnRHa) show potential. Thus, further research on FOCD in needed to identify other ACAN mutations and determine optimal treatment modalities for this patient population.

LAMA: automated image analysis for the developmental phenotyping of mouse embryos

Advanced 3D imaging modalities, such as micro-computed tomography (micro-CT), have been incorporated into the high-throughput embryo pipeline of the International Mouse Phenotyping Consortium (IMPC). This project generates large volumes of raw data that cannot be immediately exploited without significant resources of personnel and expertise. Thus, rapid automated annotation is crucial to ensure that 3D imaging data can be integrated with other multi-dimensional phenotyping data. We present an automated computational mouse embryo phenotyping pipeline that harnesses the large amount of wild-type control data available in the IMPC embryo pipeline in order to address issues of low mutant sample number as well as incomplete penetrance and variable expressivity. We also investigate the effect of developmental substage on automated phenotyping results. Designed primarily for developmental biologists, our software performs image pre-processing, registration, statistical analysis and segmentation of embryo images. We also present a novel anatomical E14.5 embryo atlas average and, using it with LAMA, show that we can uncover known and novel dysmorphology from two IMPC knockout lines.

Athletic Performance in the National Basketball Association After Arthroscopic Debridement of Osteochondral Lesions of the Talus

Background:

Use of marrow-stimulating techniques to treat osteochondral lesions of the talus (OLTs) in National Basketball Association (NBA) players is controversial.

Hypothesis:

NBA players will be able to return to preinjury playing status after treatment of OLTs by arthroscopic debridement alone without marrow-stimulating techniques.

Study Design:

Cohort study; Level of evidence, 3.

Methods:

Between the 2000 and 2015 seasons, 10 NBA players were treated with arthroscopic debridement of an OLT. The following performance outcomes were compared pre- and postoperatively: seasons played, games played, games started, minutes per game, points per game, field goals, 3-point shots, rebounds, assists, double doubles, triple doubles, steals, blocks, turnovers, personal fouls, assists per turnovers, steals per turnovers, NBA rating, scoring efficiency, and shooting efficiency. In addition, the players were compared with a matched control group using mixed effects regression and Fisher least significant difference modeling.

Results:

All 10 players returned to play in the NBA after arthroscopic debridement without microfracture or drilling of an OLT. When compared with preoperative performance, postoperative mean points scored, assists made, and steals made increased by 2.86 (P = .042), 0.61 (P = .049), and 0.15 (P = .027), respectively. Only field goal percentage decreased postoperatively when compared with matched controls; however, this normalized by the end of the second season after surgery. There was no statistically significant change in any of the other performance factors when compared with matched controls. All patients returned to basketball during the same season (n = 1) or the following season (n = 9) if the operation was performed off-season. The mean length of career after surgery was 4.1 years, with 5 players still playing in the league at the time of this study.

Conclusion:

After arthroscopic debridement of an OLT without drilling or microfracture, there was a high rate of return to the NBA, with improved points scored, assists, and steals made after surgery when compared with preoperative performance. There was no statistically significant change in any performance factors when compared with uninjured matched controls. Lesion size did not affect player career length. These data should be used to manage patients’ and teams’ expectations regarding players’ ability to return to elite levels of athletic performance after surgery of an OLT.

A novel mutation in the ACAN gene in a family with autosomal dominant short stature and intervertebral disc disease

Heterozygous mutations in the ACAN gene have been reported in individuals with short stature and advanced bone age, with or without early-onset osteoarthritis and/or osteochondritis dissecans. We report a family with a phenotypic constellation carrying a novel mutation in the ACAN gene. The proband was a 7-year-old Japanese girl with short stature. Her mother and maternal grandmother also had short stature and intervertebral disc disease. We analyzed the ACAN gene in the family and identified a novel heterozygous mutation: c.4634delT, Leu1545Profs*11.

Growth-Promoting Therapies May Be Useful In Short Stature Patients With Nonspecific Skeletal Abnormalities Caused By Acan Heterozygous Mutations: Six Chinese Cases And Literature Review

OBJECTIVE

There are numerous reasons for short stature, including mutations in osteochondral development genes. ACAN, one such osteochondral development gene in which heterozygous mutations can cause short stature, has attracted attention from researchers in recent years. Therefore, we analyzed six cases of short stature with heterozygous ACAN mutations and performed a literature review.

METHODS

Clinical information and blood samples from 6 probands and their family members were collected after consent forms were signed. Gene mutations in the probands were detected by whole-exome sequencing. Then, we searched the literature, performed statistical analyses, and summarized the characteristics of all reported cases.

RESULTS

We identified six novel mutations in ACAN: c.1411C>T, c.1817C>A, c.1762C>T, c.2266G>C, c.7469G>A, and c.1733-1G>A. In the literature, more than 200 affected individuals have been diagnosed genetically with a similar condition (height standard deviation score [SDS] -3.14 ± 1.15). Among affected individuals receiving growth-promoting treatment, their height before and after treatment was SDS -2.92±1.07 versus SDS -2.14±1.23 (P<.001). As of July 1, 2019, a total of 57 heterozygous ACAN mutations causing nonsyndromic short stature had been reported, including the six novel mutations found in our study. Approximately half of these mutations can lead to protein truncation.

CONCLUSIONS

This study used clinical and genetic means to examine the relationship between the ACAN gene and short stature. To some extent, clear diagnosis is difficult, since most of these affected individuals' characteristics are not prominent. Growth-promoting therapies may be beneficial for increasing the height of affected patients.

ABBREVIATIONS

AI = aromatase inhibitor; ECM = extracellular matrix; GnRHa = gonadotropin-releasing hormone analogue; IQR = interquartile range; MIM = Mendelian Inheritance in Man; PGHD = partial growth hormone deficiency; rhGH = recombinant human growth hormone; SDS = standard deviation score; SGA = small for gestational age; SGHD = severe growth hormone deficiency.

Evaluation of a new variant in the aggrecan gene potentially associated with chondrodysplastic dwarfism in Miniature horses

Chondrodysplastic dwarfism in Miniature horses is an autosomal recessive disorder previously associated with four mutations (D1, D2, D3*, and D4) in the aggrecan (ACAN) gene. The aim of this study was to identify additional variants in the candidate ACAN gene associated with chondrodysplastic dwarfism in Miniature horses. Fifteen dwarf Miniature horses were found to possess only one of the dwarfism-causing variants, and two possessed none of the variants. The ACAN exons (EquCab3.0) of seven dwarf Miniature horses were sequenced. A missense SNP in coding exon 11 (g.95271115A > T, c.6465A > T-RefSeq XM_005602799.2), which resulted in the amino acid substitution p.Leu2155Phe (RefSeq XP_005602856.2), was initially associated with the dwarf phenotype. The variant was tested and found present in 14 dwarf foals as well as one parent of each, and both parents of a dwarf possessing two copies. Genetic testing of 347 phenotypically normal Miniature horses demonstrated that none had more than one of the dwarf alleles or c.6465A > T. However, a study of large breeds revealed the presence of c.6465A > T, which was present in homozygosis in two Mangalarga Marchador horses. We suggest that c.6465A > T as a marker of disequilibrium or complex interactions in the Miniature horse genome could contribute to the associated dwarfism.

Aggrecan, the Primary Weight-Bearing Cartilage Proteoglycan, Has Context-Dependent, Cell-Directive Properties in Embryonic Development and Neurogenesis: Aggrecan Glycan Side Chain Modifications Convey Interactive Biodiversity

This review examines aggrecan's roles in developmental embryonic tissues, in tissues undergoing morphogenetic transition and in mature weight-bearing tissues. Aggrecan is a remarkably versatile and capable proteoglycan (PG) with diverse tissue context-dependent functional attributes beyond its established role as a weight-bearing PG. The aggrecan core protein provides a template which can be variably decorated with a number of glycosaminoglycan (GAG) side chains including keratan sulphate (KS), human natural killer trisaccharide (HNK-1) and chondroitin sulphate (CS). These convey unique tissue-specific functional properties in water imbibition, space-filling, matrix stabilisation or embryonic cellular regulation. Aggrecan also interacts with morphogens and growth factors directing tissue morphogenesis, remodelling and metaplasia. HNK-1 aggrecan glycoforms direct neural crest cell migration in embryonic development and is neuroprotective in perineuronal nets in the brain. The ability of the aggrecan core protein to assemble CS and KS chains at high density equips cartilage aggrecan with its well-known water-imbibing and weight-bearing properties. The importance of specific arrangements of GAG chains on aggrecan in all its forms is also a primary morphogenetic functional determinant providing aggrecan with unique tissue context dependent regulatory properties. The versatility displayed by aggrecan in biodiverse contexts is a function of its GAG side chains.

Hydroxytyrosol as a Promising Ally in the Treatment of Fibromyalgia

Fibromyalgia (FM) is a chronic and highly disabling syndrome, which is still underdiagnosed, with controversial treatment. Although its aetiology is unknown, a number of studies have pointed to the involvement of altered mitochondrial metabolism, increased oxidative stress and inflammation. The intake of extra virgin olive oil, and particularly of one of its phenolic compounds, hydroxytyrosol (HT), has proven to be protective in terms of redox homeostatic balance and the reduction of inflammation. In this context, using a proteomic approach with nanoscale liquid chromatography coupled to tandem mass spectrometry, the present study analysed: (i) Changes in the proteome of dermal fibroblasts from a patient with FM versus a healthy control, and (ii) the effect of the treatment with a nutritional relevant dose of HT. Our results unveiled that fibroblast from FM show a differential expression in proteins involved in the turnover of extracellular matrix and oxidative metabolism that could explain the inflammatory status of these patients. Moreover, a number of these proteins results normalized by the treatment with HT. In conclusion, our results support that an HT-enriched diet could be highly beneficial in the management of FM.

Clinical relevance of biochemical and metabolic changes in osteoarthritis

Osteoarthritis (OA) is a multifactorial disease with huge phenotypic heterogeneity. The disease affects all tissues in the joint, and the loss of articular cartilage is its hallmark. The main biochemical components of the articular cartilage are type II collagen, aggrecan, and water. Transforming growth factor-beta (TGF-β) signaling is one of the signaling pathways that maintains the healthy cartilage. However, the two subpathways of the TGF-β signaling-TGF-β and bone morphogenetic proteins (BMP) subpathways, lose their balance in OA, resulting an increased expression of cartilage degradation enzymes including matrix metallopeptidase 13 (MMP13), cathepsin B (CTSB), and cathepsin K (CTSK) and a decreased expression of aggrecan (ACAN). Thus, restoring the balance of two subpathways might provide a new avenue for treating OA patients. Further, metabolic changes are seen in OA and can be used to distinguish different subtypes of OA patients. Metabolomics studies showed that at least three endotypes of OA can be distinguished: 11% of OA patients are characterized by an elevated blood butyryl carnitine, 33% of OA patients have significant reduced arginine concentration, and 56% with metabolic alteration in phospholipid metabolism. While these findings need to be confirmed, they are promising personalized medicine tools for OA management.

Osteochondritis Dissecans of the Knee: Etiology and Pathogenetic Mechanisms. A Systematic Review

OBJECTIVE

The purpose of this manuscript is to analyze the evidence regarding etiopathogenesis of knee osteochondritis dissecans (OCD) lesions through a systematic review, so to summate the current understanding of the origin and progression of this pathologic articular processes.

DESIGN

A systematic review of the literature was performed on the PubMed and Cochrane databases on October 2017 by 2 independent authors and included all levels of evidence. This included all English language literature, pertaining specifically to etiopathology of knee OCD with exclusions for review articles and expert opinion. Of 965 identified records, 154 full-text articles were assessed for eligibility and 86 studies met the inclusion criteria.

RESULTS

According to these studies, the etiology of OCD can be of a biological or mechanical origin: 40 articles proposed a biological hypothesis, including genetic causes (27), ossification center deficit (12), and endocrine disorders (9); conversely, 52 articles supported a mechanical hypothesis, including injury/overuse (18), tibial spine impingement (5), discoid meniscus (16), and biomechanical alterations (20) as the cause of the onset of OCD. The pathogenic processes were investigated by 36 of these articles, with a focus on subchondral bone fracture and ischemia as the ultimate events leading to OCD.

CONCLUSIONS

Biological and mechanical factors are found to result in subchondral bone remodeling alterations, acting independently or more likely synergically in the progression of knee OCD. The former includes genetic causes, deficit of ossification centers and endocrine disorders; the latter, tibial spine impingement, discoid meniscus, and biomechanical alterations, together with injuries and overuse. The resultant subchondral bone ischemia and/or fracturing appears to determine the onset and progression of OCD.

LEVEL OF EVIDENCE

Systematic review of level II-IV studies, level IV.

RNA-seq reveals downregulated osteochondral genes potentially related to tibia bacterial chondronecrosis with osteomyelitis in broilers

Background

Bacterial chondronecrosis with osteomyelitis (BCO) develops in the growth plate (GP) of the proximal femur and tibia and is initiated by damage to the less mineralized chondrocytes followed by colonization of opportunistic bacteria. This condition affects approximately 1% of all birds housed, being considered one of the major causes of lameness in fast growing broilers. Although several studies have been previously performed aiming to understand its pathogenesis, the molecular mechanisms involved with BCO remains to be elucidated. Therefore, this study aimed to generate a profile of global differential gene expression involved with BCO in the tibia of commercial broilers, through RNA sequencing analysis to identity genes and molecular pathways involved with BCO in chickens.

Results

Our data showed 192 differentially expressed (DE) genes: 63 upregulated and 129 downregulated in the GP of the tibia proximal epiphysis of BCO-affected broilers. Using all DE genes, six Biological Processes (BP) were associated with bone development (connective tissue development, cartilage development, skeletal system development, organ morphogenesis, system development and skeletal system morphogenesis). The analyses of the upregulated genes did not indicate any significant BP (FDR < 0.05). However, with the downregulated genes, the same BP were identified when using all DE genes in the analysis, with a total of 26 coding genes explaining BCO in the tibia: ACAN, ALDH1A2, CDH7, CHAD, CHADL, COL11A1, COMP, CSGALNACT1, CYR61, FRZB, GAL3ST1, HAPLN1, IHH, KIF26B, LECT1, LPPR1, PDE6B, RBP4A, SERINC5, SFRP1, SOX8, SOX9, TENM2, THBS1, UCHL1 and WFIKKN2. In addition, seven transcription factors were also associated to BCO: NFATC2, MAFB, HIF1A-ARNT, EWSR1-FLI1, NFIC, TCF3 and NF-KAPPAB.

Conclusions

Our data show that osteochondral downregulated genes are potential molecular causes of BCO in broilers, and the bacterial process seems to be, in fact, a secondary condition. Sixteen genes responsible for bone and cartilage formation were downregulated in BCO-affected broilers being strong candidate genes to trigger this disorder.

Osteochondritis Dissecans Lesion Location Is Highly Concordant With Mechanical Axis Deviation

BACKGROUND

The cause of osteochondritis dissecans (OCD) is unknown.

PURPOSE

To determine if mechanical axis deviation correlates with OCD lesion location in the knee, if degree of mechanical axis deviation correlates with size of OCD lesion, and if the deformity was primarily in the distal femur or proximal tibia.

STUDY DESIGN

Cross-sectional study; Level of evidence, 3.

METHODS

We identified 61 knees that underwent osteochondral allograft (OCA) transplantation for femoral condyle OCD lesions and used preoperative lower extremity alignment radiographs to measure lower extremity mechanical axis, mechanical lateral distal femoral angle (mLDFA), mechanical medial proximal tibial angle (mMPTA), and hip-knee-ankle angle. Lesion location and area were retrieved from operative records.

RESULTS

The location of the OCD lesion was the medial femoral condyle (MFC) for 37 knees and lateral femoral condyle (LFC) for 24 knees. Among knees with MFC lesions, alignment was varus in 25 (68%). Conversely, knees with LFC lesions had valgus alignment in 16 (67%). The mLFDA was significantly more valgus in the LFC group. mMPTA was not different between MFC and LFC groups. There was no significant correlation between degree of mechanical axis deviation and lesion size.

CONCLUSION

In this cohort, two-thirds of patients with symptomatic OCD lesions had associated mechanical axis deviation. Lesion location correlated with mechanical axis deviation (LFC lesions were associated with a deformity in the distal femur). Degree of deformity was not correlated with lesion size. Mechanical axis deviation may play a role in OCD pathogenesis. These data do not allow analysis of the role of mechanical axis deviation in causation or prognosis of OCD lesions, but surgeons treating OCD should be aware of this common association.

CSGALNACT1-congenital disorder of glycosylation: A mild skeletal dysplasia with advanced bone age

Congenital disorders of glycosylation (CDGs) comprise a large number of inherited metabolic defects that affect the biosynthesis and attachment of glycans. CDGs manifest as a broad spectrum of disease, most often including neurodevelopmental and skeletal abnormalities and skin laxity. Two patients with biallelic CSGALNACT1 variants and a mild skeletal dysplasia have been described previously. We investigated two unrelated patients presenting with short stature with advanced bone age, facial dysmorphism, and mild language delay, in whom trio-exome sequencing identified novel biallelic CSGALNACT1 variants: compound heterozygosity for c.1294G>T (p.Asp432Tyr) and the deletion of exon 4 that includes the start codon in one patient, and homozygosity for c.791A>G (p.Asn264Ser) in the other patient. CSGALNACT1 encodes CSGalNAcT-1, a key enzyme in the biosynthesis of sulfated glycosaminoglycans chondroitin and dermatan sulfate. Biochemical studies demonstrated significantly reduced CSGalNAcT-1 activity of the novel missense variants, as reported previously for the p.Pro384Arg variant. Altered levels of chondroitin, dermatan, and heparan sulfate moieties were observed in patients' fibroblasts compared to controls. Our data indicate that biallelic loss-of-function mutations in CSGALNACT1 disturb glycosaminoglycan synthesis and cause a mild skeletal dysplasia with advanced bone age, CSGALNACT1-CDG.

Abnormal expression of chondroitin sulfate sulfotransferases in the articular cartilage of pediatric patients with Kashin-Beck disease

The objective of this study is to investigate the expression of enzymes involved in the sulfation of articular cartilage from proximal metacarpophalangeal (PMC) joint cartilage and distal metacarpophalangeal (DMC) joint cartilage in children with Kashin-Beck disease (KBD). The finger cartilage samples of PMC and DMC were collected from KBD and normal children aged 5-14 years old. Hematoxylin and eosin staining as well as immunohistochemical staining were used to observe the morphology and quantitate the expression of carbohydrate sulfotransferase 3 (CHST-3), carbohydrate sulfotransferase 12 (CHST-12), carbohydrate sulfotransferase 13 (CHST-13), uronyl 2-O-sulfotransferase (UST), and aggrecan. In the results, the numbers of chondrocyte decreased in all three zones of PMC and DMC in the KBD group. Less positive staining cells for CHST-3, CHST-12, CHST-13, UST, and aggrecan were observed in almost all three zones of PMC and DMC in KBD. The positive staining cell rates of CHST-12 were higher in superficial and middle zones of PMC and DMC in KBD, and a significantly higher rate of CHST-13 was observed only in superficial zone of PMC in KBD. In conclusion, the abnormal expression of chondroitin sulfate sulfotransferases in chondrocytes of KBD children may provide an explanation for the cartilage damage, and provide therapeutic targets for the treatment.

High frequency of pathogenic ACAN variants including an intragenic deletion in selected individuals with short stature

CONTEXT

Defining the underlying etiology of idiopathic short stature (ISS) improves the overall management of an individual.

OBJECTIVE

To assess the frequency of pathogenic ACAN variants in selected individuals.

DESIGN

The single-center cohort study was conducted at a tertiary university children's hospital. From 51 unrelated patients with ISS, the 16 probands aged between 3 and 18 years (12 females) with advanced bone age and/or autosomal dominant inheritance pattern of short stature were selected for the study. Fifteen family members of ACAN-positive probands were included. Exome sequencing was performed in all probands, and additional copy number variation (CNV) detection was applied in selected probands with a distinct ACAN-associated phenotype.

RESULTS

Systematic phenotyping of the study cohort yielded 37.5% (6/16) ACAN-positive probands, with all novel pathogenic variants, including a 6.082 kb large intragenic deletion, detected by array comparative genomic hybridization (array CGH) and exome data analysis. All variants were co-segregated with short stature phenotype, except in one family member with the intragenic deletion who had an unexpected growth pattern within the normal range (-0.5 SDS). One patient presented with otosclerosis, a sign not previously associated with aggrecanopathy.

CONCLUSIONS

ACAN pathogenic variants presented a common cause of familial ISS. The selection criteria used in our study were suggested for a personalized approach to genetic testing of the ACAN gene in clinical practice. Our results expanded the number of pathogenic ACAN variants, including the first intragenic deletion, and suggested CNV evaluation in patients with typical clinical features of aggrecanopathy as reasonable. Intra-familial phenotypic variability in growth patterns should be considered.

GHR gene transcript heterogeneity may explain phenotypic variability in GHR pseudoexon (6Ψ) patients

OBJECTIVES

The homozygous GH receptor (GHR) pseudoexon (6Ψ) mutation leads to growth hormone insensitivity (GHI) with clinical and biochemical heterogeneity. We investigated whether transcript heterogeneity (6Ψ-GHR to WT-GHR transcript ratio) and/or concurrent defects in other short stature (SS) genes contribute to this.

METHODS

6Ψ-GHR and WT-GHR mRNA transcripts of 4 6Ψ patient (height SDS -4.2 to -3.1) and 1 control fibroblasts were investigated by RT-PCR. Transcripts were quantified by qRT-PCR and delta delta CT analysis and compared using ANOVA with Bonferroni correction. In eleven 6Ψ patients, 40 genes known to cause GHI/SS were analysed by targeted next generation sequencing.

RESULTS

RT-PCR confirmed 6Ψ-GHR transcript in the 6Ψ patients but not control. 6Ψ-GHR transcript levels were comparable in patients 1 and 3 but significantly different among all other patients. The mean 6Ψ:WT transcript ratios ranged from 29-71:1 for patients 1-4 and correlated negatively with height SDS (R=-0.85; p<0.001). Eight deleterious variants in 6 genes were detected but the number of gene hits did not correlate with the degree of SS in individual 6Ψ patients.

CONCLUSION

Variable amounts of 6Ψ- and WT-GHR transcripts were identified in 6Ψ patients but no 6Ψ transcript was present in the control. Higher 6Ψ:WT GHR transcript ratio correlated with SS severity and may explain the phenotypic variability. Analysis of known SS genes suggested that phenotypic variation is independent of the genetic background. This is the first report of transcript heterogeneity producing a spectrum of clinical phenotypes in different individuals harbouring an identical homozygous genetic mutation.

A child with a novel ACAN missense variant mimicking a septic arthritis

Heterozygous mutations of the ACAN gene have been associated with a broad spectrum of non-lethal skeletal dysplasias, called Aggrecanopathies. We report a case of a child with severe inflammatory elbow involvement mimicking septic arthritis who carried the new ACAN missense variant c.6970 T > C, p.Trp2324Arg. The comprehensive clinical evaluation of the patient and his family, focused on the associated clinical features (facial dysmorphisms, short stature, brachydactily), led us to suspect a hereditary condition. Our findings suggest that Aggrecanopathies should be considered in children with familial short stature, poor growth spurt and joint involvement.