Genetic mapping of ossification of the posterior longitudinal ligament of the spine

Genetics of Diffuse Idiopathic Skeletal Hyperostosis and Ossification of the Spinal Ligaments

PURPOSE OF REVIEW

The study aims to provide updated information on the genetic factors associated with the diagnoses 'Diffuse Idiopathic Skeletal Hyperostosis' (DISH), 'Ossification of the Posterior Longitudinal Ligament' (OPLL), and in patients with spinal ligament ossification.

RECENT FINDINGS

Recent studies have advanced our knowledge of genetic factors associated with DISH, OPLL, and other spinal ossification (ossification of the anterior longitudinal ligament [OALL] and the yellow ligament [OYL]). Several case studies of individuals afflicted with monogenic disorders, such as X-linked hypophosphatemia (XLH), demonstrate the strong association of fibroblast growth factor 23-related hypophosphatemia with OPLL, suggesting that pathogenic variants in PHEX, ENPP1, and DMP1 are associated with FGF23-phosphate wasting phenotype and strong genetic factors placing patients at risk for OPLL. Moreover, emerging evidence demonstrates that heterozygous and compound heterozygous ENPP1 pathogenic variants inducing 'Autosomal Recessive Hypophosphatemic Rickets Type 2' (ARHR2) also place patients at risk for DISH and OPLL, possibly due to the loss of inhibitory plasma pyrophosphate (PPi) which suppresses ectopic calcification and enthesis mineralization. Our findings emphasize the importance of genetic and plasma biomarker screening in the clinical evaluation of DISH and OPLL patients, with plasma PPi constituting an important new biomarker for the identification of DISH and OPLL patients whose disease course may be responsive to ENPP1 enzyme therapy, now in clinical trials for rare calcification disorders.

Evidence for a genetic contribution to the ossification of spinal ligaments in Ossification of Posterior Longitudinal Ligament and Diffuse idiopathic skeletal hyperostosis: A narrative review

Diffuse Idiopathic Skeletal Hyperostosis (DISH) and Ossification of the Posterior Longitudinal Ligament (OPLL) are common disorders characterized by the ossification of spinal ligaments. The cause for this ossification is currently unknown but a genetic contribution has been hypothesized. Over the last decade, many studies on the genetics of ectopic calcification disorders have been performed, mainly on OPLL. Most of these studies were based on linkage analysis and case control association studies. Animal models have provided some clues but so far, the involvement of the identified genes has not been confirmed in human cases. In the last few years, many common variants in several genes have been associated with OPLL. However, these associations have not been at definitive levels of significance and evidence of functional significance is generally modest. The current evidence suggests a multifactorial aetiopathogenesis for DISH and OPLL with a subset of cases showing a stronger genetic component.

The Effect of the NFκB-USP9X-Cx43 Axis on the Dynamic Balance of Bone Formation/Degradation during Ossification of the Posterior Longitudinal Ligament of the Cervical Spine

Connexin 43- (Cx43-) mediated nuclear factor kappa-light-chain-enhancer of activated B cell (NF-κB) signaling has been found involved in the ossification of the posterior longitudinal ligament (OPLL). However, the underlying mechanism how OPLL is regulated has not been elucidated. In the present study, primary ligament fibroblast were isolated; immunoprecipitation (IP) and liquid chromatography-mass spectrometry (LC-MS) assays were applied to identify potential binding proteins of Cx43. Protein interaction was then confirmed by co-IP assay. Alkaline phosphatase (ALP) activity and alizarin red staining were used to evaluate ossification. Luciferase reporter assay and chromatin immunoprecipitation (ChIP) assay were employed to assess the binding between NF-κB p65 and target gene. Lipoxygenase inhibitor (5,8,11-eicosatriynoic acid, EPA) was applied to induce endoplasmic reticulum (ER) stress, and 4-phenylbutyrate (4-PBA) was used as an ER-stress inhibitor. Expression of USP9X, Cx43, and nuclei p65 in ligaments from patients and controls was detected by Western blotting. The results showed that ubiquitin-specific protease 9 X-chromosome (USP9X), a deubiquitylating enzyme, was a candidate of Cx43 binding proteins, and USP9X inhibited Cx43 ubiquitination. In vitro experiments showed that USP9X promoted ossification of primary ligament fibroblasts and nuclear translocation of NF-κB p65 by regulating Cx43 expression. Moreover, NF-κB can bind to the USP9X promoter to promote its transcription. When ER stress was inhibited by 4-PBA, USP9X levels, NF-κB nuclei translocation, and ALP activity were decreased. Reverse results were obtained when ER stress was induced by EPA. PDTC, an NF-κB inhibitor, could abolish the effects of EPA. Furthermore, USP9X, Cx43, and nuclei p65 were significantly upregulated in ligaments from OPLL patients than non-OPLL controls. USP9X was positively correlated with CX43 and nuclei p65 in OPLL samples. Overall, the findings suggest that the ER stress–NFκB-USP9X-Cx43 signaling pathway plays an important role in OPLL progression.

Unveiling the genetic variation of severe continuous/mixed-type ossification of the posterior longitudinal ligament by whole-exome sequencing and bioinformatic analysis

BACKGROUND CONTEXT

Ossification of the posterior longitudinal ligament (OPLL) in the cervical spine is known as a rare, complex genetic disease, its complexity being partly because OPLL is diagnosed by radiological findings regardless of clinical or genetic evaluations. Although many genes associated with susceptibility have been reported, the exact causative genes are still unknown.

PURPOSE

We performed an analysis using next-generation sequencing and including only patients with a clear involved phenotype.

STUDY DESIGN/SETTING

This was a case control study.

PATIENT SAMPLE

A total of 74 patients with severe OPLL and 26 healthy controls were included.

OUTCOME MEASURES

Causal single-nucleotide variant (SNV), gene-wise variant burden (GVB), and related pathway METHOD: We consecutively included the severe OPLL patients with continuous-/mixed-type and an occupying ratio of ≥ 40%, and performed whole-exome sequencing (WES) and bioinformatic analysis. Then, a validation test was performed for candidate variations. Participants were divided into 4 groups (rapidly-growing OPLL, growing rate ≥ 2.5%/y; slow-growing, < 2.5%/y; uncertain; and control).

RESULTS

WES was performed on samples from 74 patients with OPLL (rapidly-growing, 33 patients; slow-growing, 37; and uncertain, 4) with 26 healthy controls. Analysis of 100 participants identified a newly implicated SNV and 4candidate genes based on GVB. The GVB of CYP4B1 showed a more deleterious score in the OPLL than the control group. Comparison between the rapidly growing OPLL and control groups revealed seven newly identified SNVs. We found significant association for 2 rare missense variants; rs121502220 (odds ratio [OR] = infinite; minor allele frequency [MAF] = 0.034) in NLRP1 and rs13980628 (OR= infinite; MAF = 0.032) in SSH2. The 3 genes are associated with inflammation control and arthritis, and SSH2 and NLRP1 are also related to vitamin D modulation.

CONCLUSIONS

Identification of unique variants in novel genes such as CYP4B1 gene may induce the development of OPLL. In subgroup analysis, NLRP1 and SSH2 genes coding inflammation molecules may related with rapidly-growing OPLL.

MicroRNA-181 regulates the development of Ossification of Posterior longitudinal ligament via Epigenetic Modulation by targeting PBX1

Objectives: Ossification of the posterior longitudinal ligament (OPLL) presents as the development of heterotopic ossification in the posterior longitudinal ligament of the spine. The etiology of OPLL is genetically linked, as shown by its high prevalence in Asian populations. However, the molecular mechanism of the disease remains obscure. In this study, we explored the function and mechanism of OPLL-specific microRNAs. Methods: The expression levels of the ossification-related OPLL-specific miR-181 family were measured in normal or OPLL ligament tissues. The effect of miR-181a on the ossification of normal or pathogenic ligament cells was tested using real-time polymerase chain reaction (PCR), Western blot, alizarin red staining and alkaline phosphatase (ALP) staining. The candidate targets of miR-181 were screened using a dual luciferase reporter assay and functional analysis. The link between miR-181a and its target PBX1 was investigated using chromatin immunoprecipitation, followed by real-time PCR detection. Histological and immunohistochemical analysis as well as micro-CT scanning were used to evaluate the effects of miR-181 and its antagonist using both tip-toe-walking OPLL mice and in vivo bone formation assays. Results: Using bioinformatic analysis, we found that miR-181a-5p is predicted to play important roles in the development of OPLL. Overexpression of miR-181a-5p significantly increased the expression of ossification-related genes, staining level of alizarin red and ALP activity, while the inhibition of miR-181a-5p by treatment with an antagomir had the opposite effects. Functional analysis identified PBX1 as a direct target of miR-181a-5p, and we determined that PBX1 was responsible for miR-181a-5p's osteogenic phenotype. By chromatin immunoprecipitation assay, we found that miR-181a-5p controls ligament cell ossification by regulating PBX1-mediated modulation of histone methylation and acetylation levels in the promoter region of osteogenesis-related genes. Additionally, using an in vivo model, we confirmed that miR-181a-5p can substantially increase the bone formation ability of posterior ligament cells and cause increased osteophyte formation in the cervical spine of tip-toe-walking mice. Conclusions: Our data unveiled the mechanism by which the miR-181a-5p/PBX1 axis functions in the development of OPLL, and it revealed the therapeutic effects of the miR-181a-5p antagomir in preventing OPLL development both in vivo and in vitro. Our work is the first to demonstrate that microRNA perturbation could modulate the development of OPLL through epigenetic regulation.

Degenerative cervical myelopathy - update and future directions

Degenerative cervical myelopathy (DCM) is the leading cause of spinal cord dysfunction in adults worldwide. DCM encompasses various acquired (age-related) and congenital pathologies related to degeneration of the cervical spinal column, including hypertrophy and/or calcification of the ligaments, intervertebral discs and osseous tissues. These pathologies narrow the spinal canal, leading to chronic spinal cord compression and disability. Owing to the ageing population, rates of DCM are increasing. Expeditious diagnosis and treatment of DCM are needed to avoid permanent disability. Over the past 10 years, advances in basic science and in translational and clinical research have improved our understanding of the pathophysiology of DCM and helped delineate evidence-based practices for diagnosis and treatment. Surgical decompression is recommended for moderate and severe DCM; the best strategy for mild myelopathy remains unclear. Next-generation quantitative microstructural MRI and neurophysiological recordings promise to enable quantification of spinal cord tissue damage and help predict clinical outcomes. Here, we provide a comprehensive, evidence-based review of DCM, including its definition, epidemiology, pathophysiology, clinical presentation, diagnosis and differential diagnosis, and non-operative and operative management. With this Review, we aim to equip physicians across broad disciplines with the knowledge necessary to make a timely diagnosis of DCM, recognize the clinical features that influence management and identify when urgent surgical intervention is warranted.

Genetics of Degenerative Cervical Myelopathy: A Systematic Review and Meta-Analysis of Candidate Gene Studies

Degenerative cervical myelopathy (DCM) is estimated to be the most common cause of adult spinal cord impairment. Evidence that is suggestive of a genetic basis to DCM has been increasing over the last decade. A systematic search was conducted in MEDLINE, EMBASE, Cochrane, and HuGENet databases from their origin up to 14th December 2019 to evaluate the role of single genes in DCM in its onset, clinical phenotype, and response to surgical intervention. The initial search yielded 914 articles, with 39 articles being identified as eligible after screening. We distinguish between those contributing to spinal column deterioration and those contributing to spinal cord deterioration in assessing the evidence of genetic contributions to DCM. Evidence regarding a total of 28 candidate genes was identified. Of these, 22 were found to have an effect on the radiological onset of spinal column disease, while 12 genes had an effect on clinical onset of spinal cord disease. Polymorphisms of eight genes were found to have an effect on the radiological severity of DCM, while three genes had an effect on clinical severity. Polymorphisms of six genes were found to have an effect on clinical response to surgery in spinal cord disease. There are clear genetic effects on the development of spinal pathology, the central nervous system (CNS) response to bony pathology, the severity of both bony and cord pathology, and the subsequent response to surgical intervention. Work to disentangle the mechanisms by which the genes that are reviewed here exert their effects, as well as improved quality of evidence across diverse populations is required for further investigating the genetic contribution to DCM.

Surgical management of ossification of the posterior longitudinal ligament in the cervical spine

OPLL is a progressive process that can result in spinal cord compression and myelopathy. Various surgical approaches for the management of OPLL in the cervical spine exist. Our goal is to present our institution's experience in the management of OPLL over the last 20 years. Sixty-eight patients underwent surgery for cervical OPLL. Mean age at surgery was 56.9 years. No differences between demographic characteristics and surgical approach were identified. There were no significant differences between the approaches regarding the mean estimated blood loss, occurrence of durotomy, reoperation rate, positive K-line and preoperative cervical spine sagittal balance. Number of levels operated on was significantly different (anterior approach 2 ± 0.8 levels, posterior approach 4.3 ± 1.3 levels, combined approach 3.3 ± 0.9 levels, p-value <0.01), but postoperative sagittal balance was not (anterior approach Cobb angle 11.9 ± 5.8 degrees, posterior approach Cobb angle 7 ± 3.5 degrees, combined approach Cobb angle 16.7 ± 7.3 degrees, p-value = 0.09). Functional outcomes were good for 70% of patients and did not significantly differ across approaches (anterior approach 28%, posterior approach 33%, combined approach 9%, p-value = 0.46). Good functional outcomes were more commonly observed in patients with a positive K-line (OR 0.2, 95% CI 0.04-0.9, p-value 0.05) while poor outcomes were most commonly observed in patients with an occupational ratio >0.6 (OR 6.9, 95% CI 1.35-42.7, p-value 0.02). OPLL is a rare disease for which prompt referral for surgical decompression may lead to good clinical outcomes.

Does Ossification of the Posterior Longitudinal Ligament Progress After Fusion?

Starting in the 1960s, ossification of the posterior longitudinal ligament (OPLL) became more commonly diagnosed in Japan. The disease is characterized by a gradual increase in calcification of the posterior longitudinal ligament with the eventual sequelae of cervical canal stenosis and myelopathy. Surgical interventions to relieve stenosis and neurologic symptoms are performed to decompress the cervical canal. Studies demonstrate continued ossification of the OPLL in both nonsurgical and surgically treated patients. In this review, the authors evaluate the epidemiology, pathophysiology, and literature regarding disease progression in OPLL after cervical fusion.

Ossification of Posterior Longitudinal Ligament of Cervical Spine Among Omani Patients Referred for CT Scan at a Tertiary Care Hospital in Oman

Objectives

We sought to evaluate the proportion of ossification of the posterior longitudinal ligament (OPLL) of the cervical spine and associated factors among Omani patients.

Methods

We reviewed the cervical spine computed tomography (CT) scans of all patients referred to the Radiology Department, Sultan Qaboos University Hospital, from 2011 to 2017. Descriptive statistics were employed to determine the proportion of OPLL. We used the chi-square test to determine the association of age, gender, and diabetes mellitus with OPLL.

Results

A total of 843 patients aged ≥ 20 years were included in the study. The proportion of OPLL was 2.7% and was more frequent in men (3.2%) than women (1.9%). The male to female ratio of OPLL was 1.7:1.0. OPLL occurrence was significantly more in non-diabetic patients (p < 0.001). No significant association was found between OPLL with gender (p = 0.281) and age (p = 0.878).

Conclusions

The observed proportion of OPLL in this single-center study is relatively low, but the finding is important as the condition can eventually lead to debilitating neurologic outcomes affecting the patient's quality of life. OPLL occurrence was significantly more in non-diabetic patients, which necessitate further research on OPLL in a larger sample across Oman.

Molecular Pathophysiology of Ossification of the Posterior Longitudinal Ligament (OPLL)

Ossification of the posterior longitudinal ligament (OPLL) can be defined as an ectopic ossification in the tissues of spinal ligament showing a hyperostotic condition. OPLL is developed mostly in the cervical spine and clinical presentations of OPLL are majorly myelopathy and/or radiculopathy, with serious neurological pathology resulting in paralysis of extremities and disturbances of motility lowering the quality of life. OPLL is known to be an idiopathic and multifactorial disease, which genetic factors and non-genetic factors including diet, obesity, physical strain on the posterior longitudinal ligament, age, and diabetes mellitus, are involved into the pathogenesis. Up to now, surgical management by decompressing the spinal cord is regarded as standard treatment for OPLL, although there might be the risk of development of reprogression of ossification. The molecular pathogenesis and efficient therapeutic strategy, especially pharmacotherapy and/or preventive intervention, of OPLL has not been clearly elucidated and suggested. Therefore, in this review, we tried to give an overview to the present research results on OPLL, in order to shed light on the potential pharmacotherapy based on molecular pathophysiologic aspect of OPLL, especially on the genetic/genomic factors involved into the etiology of OPLL.

Whole-genome sequencing reveals novel genes in ossification of the posterior longitudinal ligament of the thoracic spine in the Chinese population

BACKGROUND

Ossification of the posterior longitudinal ligament (OPLL) of the spine is a complex, multifactorial disease. Although several genes that are linked to cervical OPLL susceptibility have been reported, specific genetic studies regarding thoracic OPLL are lacking. Whole-genome sequencing has been considered as an efficient strategy to search for disease-causing genes.

METHODS

We analysed whole-genome sequences in a cohort of 25 unrelated patients with thoracic OPLL. Bioinformatics analysis and various algorithms were used to predict deleterious variants. Sanger sequencing was used to confirm the variants.

RESULTS

Four deleterious mutations in three genes (c.2716C>T (p.Arg906Cys) in collagen type VI α6 (COL6A6); c.1946G>C (p.Gly649Ala) in collagen type IX α1 (COL9A1); and c.301T>C (p.Ser101Pro) and c.171A>G (p.Ile57Met) in toll-like receptor 1 (TLR1)) were successfully identified. All the variants were confirmed by Sanger sequencing.

CONCLUSION

The novel deleterious mutations of the three genes may contribute to the development of thoracic OPLL.

Abdominal fat distribution in diffuse idiopathic skeletal hyperostosis and ankylosing spondylitis patients compared to controls

AIM

To evaluate abdominal fat distribution (subcutaneous adipose tissue [SAT] and visceral adipose tissue [VAT]) in two enthesopathy-related diseases with known correlation to metabolic syndrome (MS): diffuse idiopathic skeletal hyperostosis (DISH) and ankylosing spondylitis (AS) compared with controls.

MATERIALS AND METHODS

Abdominal computed tomography (CT) examinations of 43 DISH (Resnick radiographic criteria) patients, 31 AS (Modified New York Criteria) patients and 42 age- and gender-matched (to DISH) controls (males: 29; 29; 27 and mean age: 71.7±7; 56.1±16; 72.7±8 years, respectively) were evaluated and compared for VAT and SAT surface areas on mid L3, L4, L5 levels.

RESULTS

AS patients were significantly younger compared to DISH patients and controls. No significant differences were observed between VAT and SAT of DISH and AS patients or between SAT values in all groups even after correction for age. VAT was higher in DISH and AS patients compared to controls on all three levels, but reached significance (p<0.05) only for DISH patients (L3: 24.34/23.6/18.43; L4: 23.85/22.21/18.05; L5: 19.09/18.94/14.24 mm², respectively). This did not change after correction for age. The VAT/SAT ratio was significantly larger in DISH and AS patients on all levels compared to controls.

CONCLUSION

The higher VAT surface area, a known marker for MS, which by itself is associated with bone proliferation, in DISH and AS patients compared to controls substantiates its role as a potential surrogate marker for MS as well as suggests a potential shared pathogenic pathway for enthesopathic excessive bone production in DISH and AS.

Combined use of leptin and mechanical stress has osteogenic effects on ossification of the posterior longitudinal ligament

PURPOSE

To evaluate the effects of leptin/leptin receptor (LepR) combined with mechanical stress on the development of ossification of the posterior longitudinal ligament (OPLL), which is a disease characterized by ectopic bone formation of the posterior longitudinal ligament (PLL) and can lead to radiculopathy and myelopathy.

METHODS

Six human samples of the PLL were analyzed for the expression of leptin and LepR by RT-PCR and western blotting. PLL cells were stimulated with leptin and mechanical stress delivered via a Flexcell tension system, and osteogenic differentiation was evaluated by RT-PCR and western blotting analysis of osteogenic marker expression as well as by alkaline phosphatase (ALP) staining and alizarin red S staining. Activation of mitogen-activated protein kinase (MAPK), Janus kinase (JAK) 2-signal transducer, activator of transcription (STAT) 3 and phosphatidylinositol 3-kinase (PI3K)-Akt was evaluated by western blotting.

RESULTS

Samples from the OPLL group had higher LepR mRNA and protein levels and lower leptin levels than those from healthy controls. Exposure to leptin and Flexcell increased the number of ALP-positive cells and calcium nodules in a dose-dependent manner; this effect was accompanied by upregulation of the osteogenic markers osteocalcin, runt-related transcription factor 2 (RUNX2) and osteopontin. Extracellular signal-regulated kinase, P38 MAPK, JAK2, STAT3, PI3K and Akt signaling, was also activated by the combined effects of leptin and mechanical stress.

CONCLUSIONS

Leptin and LepR are differentially expressed in OPLL tissues, and the combined use of leptin/LepR and mechanical stress promotes osteogenic differentiation of PLL cells via MAPK, JAK2-STAT3 and PI3K/Akt signaling. These slides can be retrieved under Electronic Supplementary Material.

Association of IL17RC and COL6A1 genetic polymorphisms with susceptibility to ossification of the thoracic posterior longitudinal ligament in Chinese patients

Background

In our previous whole-genome sequencing study of 30 unrelated northern Chinese Han patients, we identified six single nucleotide polymorphisms (SNPs) in the interleukin 17 receptor C (IL17RC) and collagen type VI α1 chain (COL6A1) genes that were potentially associated with thoracic ossification of the posterior longitudinal ligament (T-OPLL). To determine whether these six SNPs are associated with susceptibility to T-OPLL in the northern Chinese Han population, we performed a case-control association study to confirm specific susceptible loci in the expanded samples.

Methods

The six SNPs in the IL17RC and COL6A1 genes were analyzed in 200 northern Chinese individuals (100 patients and 100 control subjects) using the Sequenom system.

Results

The genotype distributions and allele frequencies of each SNP in the control and patient groups were compared. rs201153092, rs13051496, rs199772854, rs76999397, and rs189013166 showed potential pathogenic loci for T-OPLL in the northern Chinese Han population, whereas rs151158105 did not. At the genotype level, the differences in the genotype frequencies of rs201153092, rs13051496, rs199772854, rs76999397, and rs189013166 between T-OPLL cases and controls reached statistical significance.

Conclusions

To the best of our knowledge, this is the first association study of susceptibility genes in Han Chinese patients with T-OPLL. The results revealed five SNPs in the IL17RC and COL6A1 genes that represented potentially pathogenic mutations in patients with T-OPLL.

Role of Cx43-Mediated NFкB Signaling Pathway in Ossification of Posterior Longitudinal Ligament: An In Vivo and In Vitro Study

STUDY DESIGN

In vivo and in vitro experiments.

OBJECTIVE

To illustrate the further molecular mechanism of Cx43-mediated osteoblastic differentiation of ligament cells.

SUMMARY OF BACKGROUND DATA

Ossification of the posterior longitudinal ligament (OPLL) is one of the main causes of myelopathy in Asians, but its etiology has not been clarified. We have previously found the mechanical stress can upregulate Cx43 expression in ligament cells, which transduces mechanical signal to promote osteoblastic differentiation.

METHODS

The posterior longitudinal ligaments were collected intraoperatively. Ligament fibroblasts were isolated and cultured, and an in vitro mechanical loading model was established. In vivo and in vitro expression levels of Cx43 protein were compared between OPLL and non-OPLL patients. The activation of nuclear factor (NF)-κB (p65) signal and related inflammatory responses were detected in ligament cells under mechanical loading. The mechanical stress-induced inflammatory response and osteoblastic differentiation of OPLL cells were investigated after the treatment with Cx43 siRNA or NFкB (p65) inhibitor.

RESULTS

We first confirmed higher Cx43 levels in both in vivo ligament tissue from OPLL patients and in vitro cultured OPLL cells. We also found NFκB (p65) signal and related inflammatory response were activated by mechanical stimulation. The activation of NFκB (p65) signal was dependent upon Cx43, as its knockdown reduced signal. Moreover, treatment with Cx43 siRNA or NFкB (p65) inhibitor significantly decreased the mechanical-induced inflammation response, but partly attenuated mechanical-stimulated osteoblastic differentiation of OPLL cells.

CONCLUSION

Cx43-mediated NFкB (p65) signal played an important role in mechanical stress-induced OPLL by transduction of mechanical signal, while giving rise to the activation of inflammatory response in ligament fibroblastsLevel of Evidence: N/A.

Identification of susceptibility loci for thoracic ossification of the posterior longitudinal ligament by whole-genome sequencing

Ossification of the posterior longitudinal ligament (OPLL) is a myelopathy commonly observed in the cervical spine. By contrast, thoracic OPLL (T‑OPLL) is rare but more severe. Previous studies have identified several polymorphisms in osteogenic genes that are associated with the occurrence and development of cervical OPLL. However, few genetic studies have evaluated T‑OPLL. The present study aimed to identify the genetic factors for OPLL by performing whole‑genome sequencing (WGS) in 30 unrelated northern Chinese Han patients with T‑OPLL. Using bioinformatics analyses and damaging‑variant prediction algorithms, two deleterious variants [c.1534G>A(p.Gly512Ser)/collagen, type VI, α1 (COL6A1)] and [c.2275C>A(p.Leu759Ile)/inteleukin-17 receptor C (IL17RC)] were identified in seven unrelated patients. These two mutations resulted in markedly increased gene expression levels in peripheral blood samples. To the best of our knowledge, this is the first report to describe the use of WGS analysis of T‑OPLL in the northern Chinese Han population. The results revealed two novel potentially pathogenic mutations in patients with T‑OPLL.

The Pathogenesis of Ossification of the Posterior Longitudinal Ligament

Ossification of the posterior longitudinal ligament (OPLL) is a multi-factorial disease involving an ectopic bone formation of spinal ligaments. It affects 0.8-3.0% aging Asian and 0.1-1.7% aging European Caucasian. The ossified ligament compresses nerve roots in the spinal cord and causes serious neurological problems such as myelopathy and radiculopathy. Research in understanding pathogenesis of OPLL over the past several decades have revealed many genetic and non-genetic factors contributing to the development and progress of OPLL. The characterizations of aberrant signaling of bone morphogenetic protein (BMP) and mitogen-activated protein kinases (MAPK), and the pathological phenotypes of OPLL-derived mesenchymal stem cells (MSCs) have provided new insights on the molecular mechanisms underlying OPLL. This paper reviews the recent progress in understanding the pathophysiology of OPLL and proposes future research directions on OPLL.

Genetics Underlying an Individualized Approach to Adult Spinal Disorders

Adult spinal disorders are a significant cause of morbidity across the world and carry significant health and economic burdens. Genetic predispositions are increasingly considered for these conditions and are becoming understood. Advances in molecular technologies since the mid-1990s have made possible genetic characterizations of these diseases in many populations, and recent findings have provided insight into the underlying pathophysiologic mechanisms. These studies have made clear the genetic heterogeneity producing clinical phenotypes and suggest that individualized treatments are possible in the future. We review the genetics and heritability of cervical spondylotic myelopathy and ossification of the posterior longitudinal ligament and perform a systematic review of the genetics of adult lumbar degenerative scoliotic deformity, highlighting recent discoveries and the potential for personalized future therapeutics for these patients.

Prevalence and Distribution of Ossified Lesions in the Whole Spine of Patients with Cervical Ossification of the Posterior Longitudinal Ligament A Multicenter Study (JOSL CT study)

Ossification of the posterior longitudinal ligament (OPLL) can cause severe and irreversible paralysis in not only the cervical spine but also the thoracolumbar spine. To date, however, the prevalence and distribution of OPLL in the whole spine has not been precisely evaluated in patients with cervical OPLL. Therefore, we conducted a multi-center study to comprehensively evaluate the prevalence and distribution of OPLL using multi-detector computed tomography (CT) images in the whole spine and to analyze what factors predict the presence of ossified lesions in the thoracolumbar spine in patients who were diagnosed with cervical OPLL by plain X-ray. Three hundred and twenty-two patients with a diagnosis of cervical OPLL underwent CT imaging of the whole spine. The sum of the levels in which OPLL was present in the whole spine was defined as the OP-index and used to evaluate the extent of ossification. The distribution of OPLL in the whole spine was compared between male and female subjects. In addition, a multiple regression model was used to ascertain related factors that affected the OP-index. Among patients with cervical OPLL, women tended to have more ossified lesions in the thoracolumbar spine than did men. A multiple regression model revealed that the OP-index was significantly correlated with the cervical OP-index, sex (female), and body mass index. Furthermore, the prevalence of thoracolumbar OPLL in patients with a cervical OP-index ≥ 10 was 7.8 times greater than that in patients with a cervical OP-index ≤ 5. The results of this study reveal that the extent of OPLL in the whole spine is significantly associated with the extent of cervical OPLL, female sex, and obesity.

Targeted next-generation sequencing reveals multiple deleterious variants in OPLL-associated genes

Ossification of the posterior longitudinal ligament of the spine (OPLL), which is characterized by ectopic bone formation in the spinal ligaments, can cause spinal-cord compression. To date, at least 11 susceptibility genes have been genetically linked to OPLL. In order to identify potential deleterious alleles in these OPLL-associated genes, we designed a capture array encompassing all coding regions of the target genes for next-generation sequencing (NGS) in a cohort of 55 unrelated patients with OPLL. By bioinformatics analyses, we successfully identified three novel and five extremely rare variants (MAF < 0.005). These variants were predicted to be deleterious by commonly used various algorithms, thereby resulting in missense mutations in four OPLL-associated genes (i.e., COL6A1, COL11A2, FGFR1, and BMP2). Furthermore, potential effects of the patient with p.Q89E of BMP2 were confirmed by a markedly increased BMP2 level in peripheral blood samples. Notably, seven of the variants were found to be associated with the patients with continuous subtype changes by cervical spinal radiological analyses. Taken together, our findings revealed for the first time that deleterious coding variants of the four OPLL-associated genes are potentially pathogenic in the patients with OPLL.

Ossification of the Posterior Longitudinal Ligament: Imaging Findings in the Era of Cross-Sectional Imaging

Imaging appearance and classification systems of ossification of the posterior longitudinal ligament (OPLL) on computed tomography and magnetic resonance imaging will be reviewed. Computed tomography evaluation most accurately demonstrates OPLL length and thickness, whereas magnetic resonance imaging has the advantage of demonstrating abnormal signal in the cord. Neurologic symptoms are most common in the cervical spine and are related to the degree of spinal stenosis and presence of cord edema. Surgical treatment usually involves cases of cervical OPLL and includes anterior or posterior decompression.

Uniaxial cyclic stretch promotes osteogenic differentiation and synthesis of BMP2 in the C3H10T1/2 cells with BMP2 gene variant of rs2273073 (T/G)

Ossification of the posterior longitudinal ligament of the cervical spine (OPLL) is characterized by the replacement of ligament tissues with ectopic bone formation, and this result is strongly affected by genetic and local factors. Two single nucleotide polymorphisms (SNPs) of rs2273073 (T/G) and rs235768 (A/T) of bone morphogenetic protein 2 (BMP2) gene which are associated with OPLL have been reported in our previous report. In this study, we confirmed the connection in 18 case samples analysis of BMP2 gene in OPLL patients; additionally, it was also shown from the OPLL patients with ligament tissues that enchondral ossification and expression of BMP2 were significantly higher compared with the non-OPLL patients by histological examination, immunohistochemistry and Western blotting analysis. To investigate the underlying mechanism, we studied the effect of SNPs in cell model. The C3H10T1/2 cells with different BMP2 gene variants were constructed and then subjected to uniaxial cyclic stretch (0.5 Hz, 10% stretch). In the presence of mechanical stress, the expression of BMP2 protein in C3H10T1/2 cells transfected by BMP2 (rs2273073 (T/G)) and BMP2 (rs2273073 (T/G), rs235768 (A/T)) were significantly higher than the corresponding static groups (P<0.05). In conclusion, these results suggested that BMP2 gene variant of rs2273073 (T/G) could not only increase cell susceptibility to bone transformation similar to pre-OPLL change, but also increase the sensibility to mechanical stress which might play an important role during the progression of OPLL.

Surgical treatment for ossification of the posterior longitudinal ligament in the cervical spine

Although classically associated with patients of East Asian origin, ossification of the posterior longitudinal ligament (OPLL) may cause myelopathy in patients of any ethnic origin. Degeneration of the PLL is followed by endochondral ossification, resulting in spinal cord compression. Specific genetic polymorphisms and medical comorbidities have been implicated in the development of OPLL. Patients should be evaluated with a full history and neurologic examination, along with cervical radiographs. Advanced imaging with CT and MRI allows three-dimensional evaluation of OPLL. Minimally symptomatic patients can be treated nonsurgically, but patients with myelopathy or severe stenosis are best treated with surgical decompression. OPLL can be treated via an anterior (ie, corpectomy and fusion) or posterior (ie, laminectomy and fusion or laminoplasty) approach, or both. The optimal approach is dictated by the classification and extent of OPLL, cervical spine sagittal alignment, severity of stenosis, and history of previous surgery. Anterior surgery is associated with superior outcomes when OPLL occupies >50% to 60% of the canal, despite increased technical difficulty and higher complication rates. Posterior surgery is technically easier and allows decompression of the entire cervical spine, but patients may experience late deterioration because of disease progression.

Genetics of ossification of the posterior longitudinal ligament of the spine: a mini review

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common disease in aging populations and sometimes results in serious neurological problems due to compression of the spinal cord and nerve roots. OPLL is a multi-factorial (polygenic) disease controlled by genetic and environmental factors. Studies searching for the genetic component of OPLL, using linkage and association analyses, are in progress and several susceptibility genes have been reported. This paper reviews the recent progress in the genetic study of OPLL and comments on its future task.

The Insertion/Deletion Polymorphism of Angiotensin I Converting Enzyme Gene is Associated With Ossification of the Posterior Longitudinal Ligament in the Korean Population

OBJECTIVE

To determine whether ACE insertion/deletion (I/D) polymorphism is associated with the ossification of the posterior longitudinal ligament (OPLL) of the spine in the Korean population.

METHODS

A case-control study was conducted to investigate the association between I/D polymorphism of the angiotensin I converting enzyme (peptidyl-dipeptidase A) 1 (ACE) gene and OPLL. The 95 OPLL patients and 274 control subjects were recruited. Polymerase chain reaction for the genotyping of ACE I/D polymorphism was performed. The difference between the OPLL patients and the control subjects was compared using the contingency χ(2) test and the logistic regression analysis. For statistical analysis, SPSS, SNPStats, SNPAnalyzer, and Helixtree programs were used.

RESULTS

The genotype and allele frequencies of ACE I/D polymorphism showed significant differences between the OPLL patients and the control subjects (genotype, p<0.001; allele, p=0.009). The frequencies of D/D genotype and D allele in the OPLL group were higher than those in the control group. In logistic regression analysis, ACE I/D polymorphism was associated with OPLL (dominant model; p=0.002; odd ratio, 2.20; 95% confidence interval, 1.33-3.65).

CONCLUSION

These results suggest that the deletion polymorphism of the ACE gene may be a risk factor for the development of OPLL in the Korean population.

Genomic study of ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common disease after the middle age. OPLL frequently causes serious neurological problems due to compression of the spinal cord and/or nerve roots. OPLL occurs in patients with monogenic metabolic diseases including rickets/osteomalacia and hypoparathyroidism; however most of OPLL is idiopathic and is considered as a multi-factorial (polygenic) disease influenced by genetic and environmental factors. Genomic studies for the genetic factors of OPLL have been conducted, mainly in Japan, including linkage and association studies. This paper reviews the recent progress in the genomic study of OPLL and comments on its future direction.

Genetics and heritability of cervical spondylotic myelopathy and ossification of the posterior longitudinal ligament: results of a systematic review

STUDY DESIGN

Systematic review.

OBJECTIVE

To answer the following 3 clinical questions: (1) What is the evidence supporting a heritable predisposition for cervical spondylotic myelopathy (CSM) and ossification of the posterior longitudinal ligament (OPLL)? (2) What specific genetic polymorphisms have been associated with CSM and OPLL? (3) What is the evidence supporting a genetic basis for predicting postoperative outcomes for patients with CSM and OPLL?

SUMMARY OF BACKGROUND DATA

OPLL and CSM are thought to be multifactorial conditions resulting from a combination of environmental and genetic factors.

METHODS

A systematic review of the English language literature was undertaken for articles published between 1980 and November 7, 2012. The strength of evidence was determined by 2 independent reviewers using the Grading of Recommendation Assessment, Development and Evaluation (GRADE) criteria for studies addressing the first question of heritability and using the criteria set forth by the HuGENet Working Group in the Venice Interim Guidelines to address the last 2 questions of genetic association.

RESULTS

Of the 118 citations identified through the initial literature search, a total of 23 articles remained after application of inclusion/exclusion criteria. The 3 family association studies related to question 1 supported the principle of an inherited predisposition to CSM and OPLL; however, the strength of evidence supporting these findings was low. Within the 19 case-control studies related to question 2, 2 single nucleotide polymorphisms (COL6A1/Intron 32(-29) and COL11A2/Intron 6(-4)) were observed at higher frequencies in OPLL cases than in controls in more than 1 study and may be associated with its development. There was insufficient evidence to support an association between CSM and any specific single nucleotide polymorphism or haplotype or to support the association of specific gene alleles with postoperative CSM outcomes.

CONCLUSION

Existing family studies provide support for the principle of an inherited predisposition to CSM and OPLL. Multiple studies support the association of 2 collagen gene related single nucleotide polymorphisms with OPLL; however, there is insufficient evidence to support the association between CSM and any genetic polymorphism or to support a genetic predictor of surgical outcome. SUMMARY STATEMENTS: STATEMENT 1: Existing family studies provide support for the principle of an inherited predisposition to CSM and OPLL. STATEMENT 2: Two SNPs related to the collagen 6A1 gene (COL6A1/Intron 32(-29)) and the collagen 11A2 gene (COL11A2/Intron 6(-4)) have been associated with OPLL in multiple studies and may be associated with its development. STATEMENT 3: No statement can be made from the literature regarding the association of specific SNPs or haplotypes with CSM. STATEMENT 4: No statement can be made from the literature regarding genetic predictors of surgical outcome in the context of OPLL or CSM.

Inflammatory cytokines induce fibrosis and ossification of human ligamentum flavum cells

STUDY DESIGN

In vitro experiment using degenerated human ligamentum flavum (LF) and various inflammatory cytokines.

OBJECTIVES

To examine the effect of inflammatory cytokines on LF cells and to identify their roles in the pathogenesis of LF hypertrophy and ossification.

SUMMARY OF BACKGROUND DATA

Spinal stenosis is caused, in part, by hypertrophy and ossification of the LF, which are induced by the degenerative processes (ie, increased collagen synthesis and chondroid metaplasia) of ligament fibroblasts. Degenerated intervertebral disk spontaneously produces inflammatory cytokines, which might affect the adjacent LF through local milieu of the spinal canal.

METHODS

The interlaminar portion of the LF was collected during surgical spinal procedures in 15 patients (age range, 49-78 y) with lumbar spinal stenosis. LF fibroblasts were isolated by enzymatic digestion of LF tissue. LF cell cultures were treated with various inflammatory cytokines: interleukin (IL)-1α, IL-6, tumor necrosis factor-α (TNF-α), prostaglandin E2 (PGE2), and nitric oxide (NO). Cytotoxicity was analyzed by MTT assays. DNA synthesis was measured with H-thymidine incorporation, and mRNA expression of types I, III, V, and XI collagen and osteocalcin were performed by reverse transcription-polymerase chain reaction. Histochemical stains such as Von Kossa were also performed to detect bone nodule formation.

RESULTS

There was no cytotoxicity in the LF cells treated with each cytokine. There were significant increases in DNA synthesis and upregulated mRNA expression of types I, V, XI collagen and osteocalcin in LF cultures treated with various cytokines. LF cultures treated with IL-6, TNF-α, PGE2, and NO showed positive Von Kossa staining, indicating bone nodule formation from LF cells.

CONCLUSIONS

Inflammatory cytokines (IL-6, TNF-α, PGE2, and NO) seem to play a crucial role in hypertrophy and ossification of LF. Degenerated, herniated intervertebral disks, and facet arthrosis may influence LF through inflammatory cytokines and cause hypertrophy and ossification of LF.

Progression of lumbar spinal stenosis is influenced by polymorphism of thrombospondin 2 gene in the Korean population

PURPOSE

The aim of this study is to determine the contribution of thrombospondin 2 (THBS2) polymorphisms to the development and progression of lumbar spinal stenosis (LSS) in the Korean population.

METHODS

We studied 148 symptomatic patients with radiographically proven LSS and 157 volunteers with no history of back problems from our institution. Magnetic resonance images were obtained for all the patients and controls. Quantitative image evaluation for LSS was performed to evaluate the severity of LSS. All patients and controls were genotyped for THBS2 allele variations using a polymerase chain reaction-based technique.

RESULTS

We found no causal single nucleotide polymorphism (SNPs) in THBS2 that were significantly associated with LSS. Two SNPs (rs6422747, rs6422748) were over-represented in controls [P = 0.042, odds ratio [OR] = 0.55 and P = 0.042, OR = 0.55, respectively]. Haplotype analysis showed that the ''AGAGACG'' haplotype (HAP4) and ''AAGGACG'' haplotype (HAP5) were over-represented in severe LSS patients (P = 0.0147, OR = 2.02 and P = 0.0137, OR = 2.48, respectively). In addition, the ''AAAGGGG'' haplotype (HAP1) was over-represented in controls (P = 0.0068, OR = 0.30).

CONCLUSIONS

Although no SNPs in THBS2 were associated with LSS, haplotypes (HAP4 and HAP5) were significantly associated with progression of LSS in the Korean population, whereas another haplotype (HAP1) may play a protective role against LSS development.

Risk factors for development of myelopathy in patients with cervical spondylotic cord compression

PURPOSE

To clarify risk factors for the development of myelopathy in patients with cervical spondylotic cord compression.

METHOD

The authors reviewed articles in which risk factors for the development of myelopathy in patients with cervical spondylotic cord compression were discussed. Ossification of the posterior longitudinal ligament (OPLL) was also reviewed as a disease which causes cervical cord compression to clarify pathomechanism of the development of myelopathy.

RESULTS

Cervical motion segment disorders are considered to be multifactorial, and developmental size of the canal and foramina, pathological encroachment, biomechanical effects, and circulatory deficiencies are always present to some degree. Static and dynamic factors should be considered for the development of myelopathy. To clarify the pathomechanism of the development of myelopathy in patients with cervical spondylotic spinal cord compression, the exact natural history of CSM should be understood.

CONCLUSION

Several predictable risk factors for the development of myelopathy have been proposed in CSM or OPLL studies, but they were not definitive. Further prospective population-based study is needed to clarify the mechanism.

Association of type XI collagen genes with chronic Achilles tendinopathy in independent populations from South Africa and Australia

BACKGROUND

Type XI collagen, which is expressed in developing tendons and is encoded by the COL11A1, COL11A2 and COL2A1 genes, shares structural and functional homology with type V collagen, which plays an important role in collagen fibril assembly. We investigated the association of these three polymorphisms with Achilles tendinopathy (AT) and whether these polymorphisms interact with COL5A1 to modulate the risk of AT.

METHODS

184 participants diagnosed with chronic AT (TEN) and 338 appropriately matched asymptomatic controls (CON) were genotyped for the three polymorphisms.

RESULTS

Although there were no independent associations with AT, the TCT pseudohaplotype constructed from rs3753841 (T/C), rs1676486 (C/T) and rs1799907 (T/A) was significantly over-represented (p=0.006) in the TEN (25.9%) compared with the CON (17.1%) group. The TCT(AGGG) pseudohaplotypes constructed using these type XI collagen polymorphisms and the functional COL5A1 rs71746744 (-/AGGG) polymorphism were also significantly over-represented (p<0.001) in the TEN (25.2%) compared with the CON (9.1%) group.

DISCUSSION

The genes encoding structural and functionally related type XI (COL11A1 and COL11A2) and type V (COL5A1) collagens interact with one another to collectively modulate the risk for AT. Although there are no immediate clinical applications, the results of this study provide additional evidence that interindividual variations in collagen fibril assembly might be an important molecular mechanism in the aetiology of chronic AT.

Thoracic radiculopathy caused by ossification of the ligamentum flavum

Thoracic ossification of the ligamentum flavum (OLF) has been widely recognized as a main cause of thoracic myelopathy in Asia, particularly in Japan. However, thoracic OLF rarely causes radiculopathy. We report a rare case of thoracic radiculopathy caused by OLF. A 67-year-old male presented with a chief complaint of back pain radiating to the right of the abdomen. Neurological examination revealed mild sensory deficit at the right side of the abdomen at the T9-10 level. Magnetic resonance imaging and computed tomography demonstrated OLF at the right T9-10 level. Thoracic radiculopathy caused by OLF was suspected. Because conservative treatment was not effective to this lesion, surgical intervention was performed, and the pain disappeared immediately after the operation. Thoracic OLF rarely causes radiculopathy, but it should be considered as a differential diagnosis of thoracic radicular pain. When conservative treatment is not effective in this lesion, surgical treatment should be considered.

A genome-wide sib-pair linkage analysis of ossification of the posterior longitudinal ligament of the spine

Ossification of the posterior longitudinal ligament of the spine (OPLL) is a common musculoskeletal disease among people after middle age. The OPLL presents with serious neurological abnormalities due to compression of the spinal cord and nerve roots. The OPLL is caused by genetic and environment factors; however, its etiology and pathogenesis still remain to be elucidated. To determine the susceptibility loci for OPLL, we performed a genome-wide linkage study using 214 affected sib-pairs of Japanese. In stratification analyses for definite cervical OPLL, we found loci with suggestive linkage on 1p21, 2p22-2p24, 7q22, 16q24 and 20p12. Fine mapping using additional markers detected the highest non-parametric linkage score (3.43, P = 0.00027) at D20S894 on chromosome 20p12 in a subgroup that had no complication of diabetes mellitus. Our result would shed a new light on genetic aspects of OPLL.

Interobserver and intraobserver reliability of the classification and diagnosis for ossification of the posterior longitudinal ligament of the cervical spine

PURPOSE

Ossification of the posterior longitudinal ligament (OPLL) of the cervical spine has been classified into four types by lateral plain radiographs, but the reliability of the classification and of the diagnosis of either cervical OPLL or cervical spondylotic myelopathy (CSM) was unknown. We investigated the interobserver and intraobserver reliability of the classification and diagnosis for OPLL by radiographs and computed tomography (CT) images.

METHODS

A total of 16 observers classified each patient's images into five groups; OPLL continuous, segmental, mixed, circumscribed type, or CSM. To evaluate interobserver reliability, the observers first classified only radiograph images, and next both radiographs and CT images. On another day they followed the same procedure to evaluate intraobserver reliability. We also evaluated interobserver and intraobserver reliability of the diagnosis of either cervical OPLL or CSM.

RESULTS

Interobserver reliability of the classification with radiographs only showed moderate agreement, but interobserver reliability with both radiographs and CT images showed substantial agreement. Intraobserver of reliability the classification was also improved by additional CT images. Interobserver reliability of the diagnosis with both radiographs and CT images was almost similar to with radiographs only. Intraobserver reliability of the diagnosis was improved by additional CT images.

CONCLUSIONS

This study suggested that the reliability of the classification and diagnosis for cervical OPLL was improved by additional CT images. We propose that diagnostic criteria for OPLL include both radiographs and CT images.

Does ossification of the posterior longitudinal ligament progress after laminoplasty? Radiographic and clinical evidence of ossification of the posterior longitudinal ligament lesion growth and the risk factors for late neurologic deterioration

Ossification of the posterior longitudinal ligament (OPLL) is a disease process characterized by progressive growth and calcification resulting in spinal canal compromise and serious neurological sequelae in advanced cases. Historically, OPLL has most commonly been treated with posterior surgical decompression. Although this procedure indirectly decompresses the spinal cord, it does not address the offending pathological entity, and further growth of the lesion may result in delayed neurological deterioration. This fact is particularly relevant because a number of long-term studies have revealed both longitudinal and transverse disease progression in individuals treated both surgically and conservatively. Despite these high rates of radiographically documented progression, however, the rate of neurological decline in patients undergoing posterior surgery with laminoplasty is low. In this article, the authors review the pathophysiology of OPLL, evidence of disease progression, and outcome data addressing conservative and surgical treatments.

Ossification of the posterior longitudinal ligament of the cervical spine: etiology and natural history

STUDY DESIGN

Review article.

OBJECTIVE

To review the etiology, natural history, measurement tools, and image diagnosis of ossification of the posterior longitudinal ligament (OPLL) of the cervical spine.

SUMMARY OF BACKGROUND DATA

OPLL is a well-known disease that causes myelopathy. Genetic factors are very important for development of OPLL. However, the pathogenetic gene and natural history of OPLL have not been clarified.

METHODS

The authors reviewed studies about the etiology, natural history, measurement tools, and diagnosis of OPLL, which had been performed by the members of the Investigation Committee on the Ossification of the Spinal Ligaments of the Japanese Ministry of Health, Labour, and Welfare.

RESULTS

The prevalence of OPLL in the general Japanese population was reported to be 1.9% to 4.3% among people older than 30 years. Genetic factors are important for development of OPLL, and some candidate genes have been reported. Clinical course of OPLL has been clarified by a prospective long-term follow-up study. Some radiographic predictors for development of myelopathy were introduced. Image diagnosis of OPLL is easy by plain radiographs, but magnetic resonance imaging and computed tomography are useful to determine cord compression by OPLL.

CONCLUSION

OPLL should be managed on the basis of the consideration of its natural history. Elucidation of pathogenetic genes of OPLL will introduce a new approach for management of OPLL.

Ossification of the posterior longitudinal ligament: genetics and pathophysiology

Ossification of the posterior longitudinal ligament (OPLL) is a disease of progressive ectopic calcification of the PLL of the spine. It occurs most frequently in the cervical spine, followed by the thoracic spine. The disease was first described in the Japanese population, and the prevalence of OPLL is highest in Japan at a rate of 1.9%-4.3%. Note, however, that OPLL is also seen and is a known cause of cervical myelopathy in other Asian countries and in the white population. Research into the underlying cause of OPLL over the past few decades has shown that it is a multifactorial disease with significant genetic involvement. Genetic studies of OPLL have revealed several gene loci that may be involved in the pathogenesis of this disease. Genes encoding for proteins that process extracellular inorganic phosphate, collagen fibrils, and transcription factors involved in osteoblast and chondrocyte development and differentiation have all been implicated in the pathophysiology of OPLL. In this paper, the authors review current understanding of the genetics and pathophysiology of OPLL.

The genetics of ossification of the posterior longitudinal ligament

OBJECT

Ossification of the posterior longitudinal ligament (OPLL) is a pathological process of ectopic calcification with a preponderance for the cervical spine. Epidemiological and familial studies have both indicated predisposition; however, the genetic inheritance pattern and responsible genes for OPLL are still uncertain. The aim of this study was to evaluate and summarize the current understanding of the genetics underlying OPLL.

METHODS

The authors reviewed epidemiological and genetic studies surrounding OPLL, with a particular focus on inheritance patterns and potential genes responsible for OPLL, using a PubMed database literature search.

RESULTS

Despite an unclear inheritance pattern, there appears to be a strong familial link in patients with OPLL. Examination of these patterns using linkage analysis has shown multiple candidate genes that could be responsible for the inheritance of OPLL. Genes for collagen, nucleotide pyrophosphatase, transforming growth factors, and the vitamin D receptor have all been implicated. Additionally, multiple cytokines and growth factors, including bone morphogenetic proteins as well as other proteins and interleukins involved in bone development, have been shown to be abnormally expressed in patients with OPLL. In addition, multiple mechanical and metabolic factors such as hyperinsulinemia and obesity have been shown to be linked to OPLL.

CONCLUSIONS

Ossification of the posterior longitudinal ligament has a complex inheritance pattern. It does not appear that OPLL follows a simple, single-gene Mendelian inheritance pattern. Development of OPLL is more likely multifactorial in nature and develops in patients with a genetic predisposition from a variety of different mutations in various genes on various chromosomes. Additionally, environmental factors and interaction by other pathological disease processes, such as obesity and diabetes mellitus, may play a role in the development of OPLL in susceptible individuals.

Analysis of demographics, risk factors, clinical presentation, and surgical treatment modalities for the ossified posterior longitudinal ligament

OBJECT

Ossification of the posterior longitudinal ligament (OPLL) is a rare disease that results in progressive myeloradiculopathy related to pathological ossification of the ligament from unknown causes. Although it has long been considered a disease of Asian origin, this disorder is increasingly being recognized in European and North American populations. Herein the authors present demographic, radiographic, and comorbidity data from white patients with diagnosed OPLL as well as the outcomes of surgically treated patients.

METHODS

Between 1999 and 2010, OPLL was diagnosed in 36 white patients at Barrow Neurological Institute. Patients were divided into 2 groups: a group of 33 patients with cervical OPLL and a group of 3 patients with thoracic or lumbar OPLL. Fifteen of these patients who had received operative treatment were analyzed separately. Imaging analysis focused on signal changes in the spinal cord, mass occupying ratio, signs of dural penetration, spinal levels involved, and subtype of OPLL. Surgical techniques included anterior cervical decompression and fusion with corpectomy, posterior laminectomy with fusion, posterior open-door laminoplasty, and anterior corpectomy combined with posterior laminectomy and fusion. Comorbidities, cigarette smoking, and previous spine surgeries were considered. Neurological function was assessed using a modified Japanese Orthopaedic Association Scale (mJOAS).

RESULTS

A high-intensity signal on T2-weighted MR imaging and a history of cervical spine surgery correlated with worse mJOAS scores. Furthermore, mJOAS scores decreased as the occupying rate of the OPLL mass in the spinal canal increased. On radiographic analysis, the proportion of signs of dural penetration correlated with the OPLL subtype. A high mass occupying ratio of the OPLL was directly associated with the presence of dural penetration and high-intensity signal. In the surgical group, the rate of neurological improvement associated with an anterior approach was 58% compared with 31% for a posterior laminectomy. No complications were associated with any of the 4 types of surgical procedures. In 3 cases, symptoms had worsened at the last follow-up, with only a single case of disease progression. Laminoplasty was the only technique associated with a worse clinical outcome. There were no statistical differences (p > 0.05) between the type of surgical procedure or radiographic presentation and postoperative outcome. There was also no difference between the choice of surgical procedure performed and the number of spinal levels involved with OPLL.

CONCLUSIONS

Ossification of the posterior longitudinal ligament can no longer be viewed as a disease of the Asian population exclusively. Since OPLL among white populations is being diagnosed more frequently, surgeons must be aware of the most appropriate surgical option. The outcomes of the various surgical treatments among the different populations with OPLL appear similar. Compared with other procedures, however, anterior decompression led to the best neurological outcomes.

Association between interleukin 15 receptor, alpha (IL15RA) polymorphism and Korean patients with ossification of the posterior longitudinal ligament

OBJECTIVES

Recently, a number of evidences have been reported concerning the genetic factor involved in the development of ossification of the posterior longitudinal ligament (OPLL). The purpose of this study was to investigate single nucleotide polymorphisms (SNPs) of the interleukin 15 receptor, alpha (IL15RA) gene as a risk factor in Korean patients with OPLL.

DESIGN

To investigate the genetic association, two coding SNPs (rs2296139, Thr73Thr; rs2228059, Asn182Thr) in IL15RA were genotyped in 166 OPLL patients and 230 control subjects. SNPStats, SNPAnalyzer, and Helixtree programs were used for association analysis.

RESULTS

In the present study, we found the association between a missense SNP (rs2228059) and the risk of OPLL in codominant (p = 0.0028, OR = 1.58, 95% CI = 1.17-2.14), dominant (p = 0.0071, OR = 1.82, 95% CI = 1.17-2.82), and recessive models (p = 0.036, OR = 1.79, 95% CI = 1.04-3.09). The frequency of rs2228059 allele was significantly associated with the susceptibility of OPLL (p = 0.0043, OR = 1.52, 95% CI = 1.14-2.02). After Bonferroni correction, the missense SNP (rs2228059, Asn182Thr) still had significant correlations (p = 0.0056 in codominant model; p = 0.0142 in dominant model; p = 0.0086 in allele analysis). Haplotype variation in IL15RA was associated with OPLL (global haplotype test, p = 0.025).

CONCLUSIONS

These results suggest that IL15RA polymorphism may be associated with the susceptibility of OPLL in Korean population.