A promoter polymorphism of tissue inhibitor of metalloproteinase-2 gene is associated with severity of thoracic adolescent idiopathic scoliosis

Genetics and pathogenesis of scoliosis

Background

Scoliosis is defined as a lateral spine curvature of at least 10° with vertebral rotation, as seen on a posterior-anterior radiograph, often accompanied by reduced thoracic kyphosis. Scoliosis affects all age groups: idiopathic scoliosis is the most common spinal disorder in children and adolescents, while adult degenerative scoliosis typically affects individuals over fifty. In the United States, approximately 3 million new cases of scoliosis are diagnosed annually, with a predicted increase in part due to global aging. Despite its prevalence, the etiopathogenesis of scoliosis remains unclear.

Methods

This comprehensive review analyzes the literature on the etiopathogenetic evidence for both idiopathic and adult degenerative scoliosis. PubMed and Google Scholar databases were searched for studies on the genetic factors and etiopathogenetic mechanisms of scoliosis development and progression, with the search limited to articles in English.

Results

For idiopathic scoliosis, genetic factors are categorized into three groups: genes associated with susceptibility, disease progression, and both. We identify gene groups related to different biological processes and explore multifaceted pathogenesis of idiopathic scoliosis, including evolutionary adaptations to bipedalism and developmental and homeostatic spinal aberrations. For adult degenerative scoliosis, we segregate genetic and pathogenic evidence into categories of angiogenesis and inflammation, extracellular matrix degradation, neural associations, and hormonal influences. Finally, we compare findings in idiopathic scoliosis and adult degenerative scoliosis, discuss current limitations in scoliosis research, propose a new model for scoliosis etiopathogenesis, and highlight promising areas for future studies.

Conclusions

Scoliosis is a complex, multifaceted disease with largely enigmatic origins and mechanisms of progression, keeping it under continuous scientific scrutiny.

Single Nucleotide Polymorphisms and Adolescent Idiopathic Scoliosis: A Systematic Review and Meta-Analysis of the Literature

STUDY DESIGN

Meta-analysis.

OBJECTIVE

To determine the single nucleotide polymorphisms (SNPs) that are related to adult idiopathic scoliosis.

SUMMARY AND BACKGROUND DATA

Adolescent idiopathic scoliosis (AIS) is considered one of the most prevalent spinal diseases. Even though the cause of AIS is yet to be determined, family history and sex have shown conclusive associations. Multiple studies have indicated that AIS is more prevalent in families where at least one other first-degree relative is similarly affected, indicating a possible genetic etiology to AIS.

MATERIALS AND METHODS

Articles were collected from 3 different search engines and then processed in 2 stages for final article selection for quantitative analysis. Five different genetic models were represented to show the association between the different SNPs and AIS. The Hardy-Weinberg equilibrium was examined using Fisher exact test, with significance set at P <0.05. The final analysis paper's quality was evaluated using the Newcastle Ottawa Scale. Kappa interrater agreement was calculated to evaluate the agreement between authors.

RESULTS

The final analysis comprised 43 publications, 19412 cases, 22005 controls, and 25 distinct genes. LBX1 rs11190870 T>C and MATN-1 SNPs were associated with an increased risk of AIS in one or all of the 5 genetic models. IGF-1 , estrogen receptor alfa, and MTNR1B , SNPs were not associated with AIS in all 5 genetic models. Newcastle Ottawa Scale showed good quality for the selected articles. Cohen k = 0.741 and Kappa interrater agreement of 84% showed that the writers were in strong agreement.

CONCLUSIONS

There seem to be associations between AIS and genetic SNP. Further larger studies should be conducted to validate the results.

Predictive value of single-nucleotide polymorphisms in curve progression of adolescent idiopathic scoliosis

PURPOSE

Genetic diagnosis is a promising approach because several single-nucleotide polymorphisms (SNPs) associated with adolescent idiopathic scoliosis (AIS) progression have been reported. We review the predictive value of SNPs in curve progression of adolescent idiopathic scoliosis.

METHODS

We reviewed DNA-based prognostic testing to predict curve progression. Then, the multiple polymorphisms in loci related to AIS progression were also reviewed, and we elucidated the predictive value of SNPs from four functional perspectives, including endocrine metabolism, neuromuscular system, cartilage and extracellular matrix, enzymes, and cytokines.

RESULTS

The ScoliScores were less successful predictors than expected, and the weak power of predictive SNPs might account for its failure. Susceptibility loci in ESR1, ESR2, GPER, and IGF1, which related to endocrine metabolism, have been reported to predict AIS progression. Neuromuscular imbalance might be a potential mechanism of scoliosis, and SNPs in LBX1, NTF3, and SOCS3 have been reported to predict the curve progression of AIS. Susceptibility loci in SOX9, MATN1, AJAP1, MMP9, and TIMP2, which are related to cartilage and extracellular matrix, are also potentially related to AIS progression. Enzymes and cytokines play essential roles in regulating bone metabolism and embryonic development. SNPs in BNC2, SLC39A8, TGFB1, IL-6, IL-17RC, and CHD7 were suggested as predictive loci for AIS curve progression.

CONCLUSIONS

Many promising SNPs have been identified to predict the curve progression of AIS. However, conflicting results from replication studies and different ethnic groups hamper their reliability. Convincing SNPs from multiethnic populations and functional verification are needed.

Genetic variants of tissue inhibitors of matrix metalloproteinase 1 (rs4898) and 2 (rs8179090) in diverticulosis

INTRODUCTION

Diverticulosis affects approximately 60% of population after 60th year of age. Diverticular disease is symptomatic diverticulosis characterized by abdominal pain, flatulence and bloating, and bowel habits change. Age and lifestyle are risk factors for diverticulosis, additionally genetic predisposition is postulated. The aim of the study was to assess whether tissue inhibitors of matrix metalloproteinase (TIMP) 1 rs4898 and TIMP2 rs8179090 genetic variants are related to colonic diverticulosis.

METHODS

The study included 220 patients, 100 with colon diverticulosis diagnosed on colonoscopy and 120 controls. TIMP1 rs4898 and TIMP2 rs8179090 variants were examined using PCR-restriction fragments length polymorphism from a blood sample.

RESULTS

Allele T of TIMP1 rs4898 was more frequent in male patients with diverticulosis than in controls (P < 0.01), whereas in women there were no differences in its distribution, both in heterozygotes and homozygotes or in homozygotes separately, proving a recessive effect. TIMP2 s8179090 allele G frequency was 0.95 in cases and controls, there were no CC homozygotes identified, and no associations with diverticulosis showed.

CONCLUSION

TIMP1 rs4898 allele T may be a genetic determinant of the risk of diverticulosis in men.

Idiopathic scoliosis: general characteristics and analysis of etiological theories (literature review)

Idiopathic scoliosis is a severe pathology of the musculoskeletal system that affects children and adolescents all over the world. The disease occurs in approximately 0.2-0.6% of the general population, and is the largest subgroup of spinal curvature in humans (70-90% of all known scoliosis cases). In idiopathic scoliosis, a threedimensional deformation of the vertebral column is formed, leading to the formation of a rib hump, curvature of the ribs and chest, asymmetry of the pelvis and impaired development of internal organs. The main feature of the disease is the spontaneous development of deformity during the growth of the child and the tendency to progress. Scoliosis is not only an orthopedic disease, but also a ignificant cosmetic, and, consequently, a psychological and social problem. The standard of treatment for scoliotic disease remains unchanged for a long time: observation, corset treatment and surgical correction. The prognosis for the development of pathology varies depending on the degree of deformation. The corset-therapy, hospitalization, surgery and treatment of chronic back pain have a negative impact on the psychoemotional state of children and adolescents. Despite significant advances in the methods of diagnosis of deformity, improvement of surgical treatment methods and in the study of pathogenesis, the etiological factor of pathology is still unknown. The search for the causes of idiopathic scoliosis covers almost all aspects of its possible origin: genetic, environmental, hormonal, metabolic, biochemical, neurological, and others. In recent decades, relevant theories of the development of scoliosis have been formulated, but none of the theories reveals the essence of the pathological process and has no clear justification. The greatest number of supporters is the genetic theory: genetic factors play a key role in the occurrence and development of idiopathic scoliosis. Understanding the underlying factors of the disease will enable prevention, early diagnosis, and identification of the risk groups of the patients in question.

Etiopathogenesis of adolescent idiopathic scoliosis: Review of the literature and new epigenetic hypothesis on altered neural crest cells migration in early embryogenesis as the key event

Adolescent idiopathic scoliosis (AIS) affects 2-3% of children. Numerous hypotheses on etiologic/causal factors of AIS were investigated, but all failed to identify therapeutic targets and hence failed to offer a cure. Therefore, currently there are only two options to minimize morbidity of the patients suffering AIS: bracing and spinal surgery. From the beginning of 1960th, spinal surgery, both fusion and rod placement, became the standard of management for progressive adolescent idiopathic spine deformity. However, spinal surgery is often associated with complications. These circumstances motivate AIS scientific community to continue the search for new etiologic and causal factors of AIS. While the role of the genetic factors in AIS pathogenesis was investigated intensively and universally recognized, these studies failed to nominate mutation of a particular gene or genes combination responsible for AIS development. More recently epigenetic factors were suggested to play causal role in AIS pathogenesis. Sharing this new approach, we investigated scoliotic vertebral growth plates removed during vertebral fusion (anterior surgery) for AIS correction. In recent publications we showed that cells from the convex side of human scoliotic deformities undergo normal chondrogenic/osteogenic differentiation, while cells from the concave side acquire a neuronal phenotype. Based on these facts we hypothesized that altered neural crest cell migration in early embryogenesis can be the etiological factor of AIS. In particular, we suggested that neural crest cells failed to migrate through the anterior half of somites and became deposited in sclerotome, which in turn produced chondrogenic/osteogenic-insufficient vertebral growth plates. To test this hypothesis we conducted experiments on chicken embryos with arrest neural crest cell migration by inhibiting expression of Paired-box 3 (Pax3) gene, a known enhancer and promoter of neural crest cells migration and differentiation. The results showed that chicken embryos treated with Pax3 siRNA (microinjection into the neural tube, 44 h post-fertilization) progressively developed scoliotic deformity during maturation. Therefore, this analysis suggests that although adolescent idiopathic scoliosis manifests in children around puberty, the real onset of the disease is of epigenetic nature and takes place in early embryogenesis and involves altered neural crest cells migration. If these results confirmed and further elaborated, the hypothesis may shed new light on the etiology and pathogenesis of AIS.

TIMP2 Polymorphisms Association With Curve Initiation and Progression of Thoracic Idiopathic Scoliosis in the Caucasian Females

Idiopathic scoliosis (IS) etiology remains unclear, but strong genetic background is suggested. Previously reported TIMP2 study indicates an association of genic rs8179090 with IS progression in a Han Chinese population. However, there has been a lack of investigation into intragenic TIMP2 polymorphisms in IS patients. We recruited 100 Caucasian females with IS and 100 controls. Patients were subdivided accordingly to: progression rate, curve severity, joint mobility, and curve pattern. Allele-specific-polymerase chain reaction based on fluorescence resonance energy transfer was applied to evaluate nine TIMP2 polymorphisms. Distribution of genotype and allele frequency in only one polymorphism (rs11658743) differed in case-control study. Four of the polymorphisms (rs2277700, rs11077401, rs2376999, and rs4789934) showed non-equal distributions either in genotype or/and allele distributions in the patients of different progression rates. The rs11077401 was related to curve severity patients distinction and the rs8179090 distinguished patients with different joint mobility level. Two polymorphisms either differed statistically in case of curve patterns subgrouping (rs8068674 and rs8179090) or showed a slight tendency toward significance in the recessive model of allele distributions (rs9916809 and rs8179090). The remaining two polymorphisms (rs2377005, rs11658743) showed no association with either clinical or radiographic IS characteristics. The influence of the G allele of the rs8179090 on the clinical course of IS has not yet been confirmed. We identified four TIMP2 polymorphisms (rs11077401, rs2376999, rs2277700, and rs4789934) that were associated with a higher risk of the progressive IS form. Further genetic association studies based on suggested clinical criteria would be necessary to validate TIMP2 polymorphisms associated with the curve progression. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:2217-2225, 2019.

Development of Novel Animal Model for Studying Scoliosis Using a Noninvasive Method and Its Validation through Gene-Expression Analysis

STUDY DESIGN

To induce scoliosis in young female Wistar rats using a noninvasive method and to validate this model.

PURPOSE

To induce scoliosis in a rat model noninvasively by bracing and to study the corresponding gene-expression profile in the spine and different organs.

OVERVIEW OF LITERATURE

Scoliosis involves abnormal lateral curvature of the spine, the causes of which remain unclear. In the literature, it is suggested that scoliosis is genetically heterogeneous, as there are multiple factors involved directly or indirectly in its pathogenesis. Clinical and experimental studies were conducted to understand the etiology of anatomical alterations in the spine and internal organs, as the findings could help clinicians to establish new treatment approaches.

METHODS

Twelve female Wistar rats aged 21 days were chosen for this study. Customized braces and real-time polymerase chain reaction (RT-PCR) primers for rats were designed using Primer 3 software. Radiological analysis (X-rays), histopathological studies, SYBR green, and RT-PCR analysis were performed.

RESULTS

The spines of six rats were braced in a deformed position, which resulted in a permanent structural deformity as confirmed by X-ray studies. The remaining rats were used as controls. Quantitative studies of the expression of various genes (osteocalcin, pleiotrophins, matrix metalloproteinase-2 [MMP2] and MMP9, TIMP, interleukins 1 and 6, tumor necrosis factor-α) showed their differential expression and significant upregulation (p<0.05) in different organs of scoliotic rats in comparison to those in control rats. Histopathological findings showed tissue necrosis and fibrosis in the brain, retina, pancreas, kidney, liver, and disc of scoliotic rats.

CONCLUSIONS

Bracing is a noninvasive method for inducing scoliosis in an animal model with 100% reliability and with corresponding changes in gene expression. Scoliosis does not just involve a spine deformity, but can be referred to as a systemic disease on the basis of the pathological changes observed in various internal organs.

Positive Association between TGFB1 Gene and Susceptibility to Idiopathic Scoliosis in Bulgarian Population

Idiopathic scoliosis (IS) is a common medical condition beginning in childhood and characterized by strong evidence for a genetic susceptibility to three-dimensional spinal deformity. The primary goal of the current case-control study is to examine the association between the TGFB1 (-509C/T) functional polymorphic variant and genetic predisposition to IS in the Bulgarian population and the genotype-phenotype correlations in distinct case-control subgroups based on age at onset, family history, and gender. A total of 127 patients with primary scoliosis and 254 gender-matched control subjects were recruited. The mean Cobb angle was 53.8 ± 21.2°. Genotyping of cases and controls was performed using the TaqMan real-time amplification technique. The results were processed statistically using Pearson's Chi-squared test and Fisher's exact test with a value of p less than 0.05 as statistically significant. The polymorphic T allele and TT genotype were associated with a greater incidence of IS and can be considered as predisposing factors with a moderate effect on deformity development. The current results suggested that there was a genetic predisposition in early and late onset IS and familial, sporadic, and female cases. Nevertheless, replication studies are needed to reveal the relationship between the TGFB1 locus and certain subtypes of IS in different populations.

Etiological Theories of Adolescent Idiopathic Scoliosis: Past and Present

Adolescent idiopathic scoliosis is one of the most common spinal deformities, yet its cause is unknown. Various theories look to biomechanical, neuromuscular, genetic, and environmental origins, yet our understanding of scoliosis etiology is still limited. Determining the cause of a disease is crucial to developing the most effective treatment. Associations made with scoliosis do not necessarily point to causality, and it is difficult to determine whether said associations are primary (playing a role in development) or secondary (develop as a result of scoliosis). Scoliosis is a complex condition with highly variable expression, even among family members, and likely has many causes. These causes could be similar among homogenous groups of AIS patients, or they could be individual. Here, we review the most prevalent theories of scoliosis etiology and recent trends in research.

Validity and reliability of photographic measures to evaluate waistline asymmetry in idiopathic scoliosis

OBJECTIVE

Evaluate the relationship between radiological, clinical and perceived waistline asymmetry (WLA) in a sample of idiopathic scoliosis (IS) patients.

METHODS

77 patients were included (mean age 20.3 years; 85 % women). We obtained a full X-ray of the spine and back clinical photography for all patients. On photographs, waist height angle (WHA), right/left waist angles (WA) and right/left waistline distance ratio were measured. SRS22, Trunk Appearance Perception Scale (TAPS) and Spinal Appearance Questinnaire (SAQ) questionnaires were also completed. The intra and inter-observer reliability of each photographic measure was assessed. A correlation analysis between all variables was done using Pearson Correlations Coefficient.

RESULTS

All measures reported have excellent intra- and inter-observer (ICC ≥0.8) reliability. A significant correlation was found between WHA and Cobb angle, mainly with Main Thoracic (MT) (r = -0.56). Right and left waist angles, and especially the difference between them (RLWAD), is related to the thoracolumbar/lumbar (TLL) curve. We have found a significant correlation between RLWAD and TLL curve magnitude (r = -0.54) and with the inclination of the lower end vertebra (LEV) (r = 0.74). Only WHA has a significant, but poor correlation (r ≅ 0.3) with trunk perception scales (TAPS and SAQ). No other significant correlations were found between WLA measures and patient related outcome scores.

CONCLUSION

WLA measures proposed in this article are reliable tools to assess WLA. We have found a significant correlation between clinical WLA and skeletal deformity (Cobb angle). WHA is related with MT curve while the RLWAD depends on the TLL curve magnitude and its LEV. We have also found a significant relation between WHA and the patient's perception of the deformity. It seems that WLA is a cosmetic concern to take into account in clinical evaluation of IS patients.

Replication of Association Between 53 Single-Nucleotide Polymorphisms in a DNA-Based Diagnostic Test and AIS Progression in Chinese Han Population

STUDY DESIGN

A case-only study.

OBJECTIVE

The aim of this study was to evaluate the association of the 53 single-nucleotide polymorphisms (SNPs) in a prognostic test with curve progression in Chinese adolescent idiopathic scoliosis (AIS) patients.

SUMMARY OF BACKGROUND DATA

"ScoliScore" was the first diagnostic kit developed for curve progression of AIS in the white population. To date, there is still a paucity of validation of ScoliScore in Chinese Han population.

METHODS

A total of 670 AIS patients were included in the study, with 313 patients assigned to the nonprogression group and the other 357 patients assigned to the progression group. A panel of 53 SNPs encompassed in ScoliScore were genotyped using the PCR-based Invader assay. The allele frequencies were compared between AIS patients with progressive curve and those with nonprogressive curve.

RESULTS

SNP rs9945359 and rs17044552 are the only 2 SNPs that had significantly different allele frequencies between the 2 groups. Allele A of rs9945359 was significantly higher in the progression group than in the nonprogression group (25.7% vs 19.5%, P = 0.01), and allele A of rs17044552 was significantly lower in the progression group (11.5% vs 16.4%, P = 0.01). The odds ratio (OR) of these 2 SNPs were 1.42 [95% confidence interval (95% CI) 1.09-1.88] and 0.65 (95% CI 0.47-0.91), respectively. As for the allele frequencies of the other 51 SNPs, no significant difference was found between the 2 groups.

CONCLUSION

ScoliScore could not be able to predict the curve progression of AIS in Chinese Han population. However, the role of this test in other populations cannot be totally excluded, and additional replication studies in other ethnic groups are warranted to evaluate the significance of these SNPs.

LEVEL OF EVIDENCE

4.

Understanding the Basis of Genetic Studies: Adolescent Idiopathic Scoliosis as an Example

STUDY DESIGN

A review of the general concepts of genetics studies with specific reference to adolescent idiopathic scoliosis (AIS).

OBJECTIVES

To equip the average spine surgeon with the vocabulary and understanding needed to understand the genetics of scoliosis and the approaches used to identify risk genes.

SUMMARY OF BACKGROUND DATA

Adolescent idiopathic scoliosis is a multifactorial disease. Increasing evidence from families and monozygotic twins suggests the involvement of genetic factors. An estimation of heritability also indicates a strong influence of genetics on the disease. Increasing focus has been placed on identifying genes and genetic variants associated with AIS.

REVIEW

This is a review of genes and genetic variations, the phenotype definition of AIS in genetics studies, concepts and approaches to identifying associated genes, and the evaluation of results. Different types of genetic variations are present in the genome. These variations may modulate the expression or function of protein products, which in turn alter individuals' susceptibility to disease. Identifying the variants related to AIS requires an objective and clearly defined phenotype, among which the Cobb angle is commonly used. The phenotype helps classify subjects into cases and controls. By selecting candidate genes of growth factors and hormonal receptors, which are speculated to be involved in the mechanism of disease, the variants within these genes were compared between cases and controls to identify any differences. Another approach was to use large families and inspect the co-segregation of variants and phenotypes. Recently, arrays covering the variants of the whole genome were developed and assist in high-throughput screening for associated genes.

CONCLUSIONS

Genetic factors have an important role in AIS. Deciphering the genes and genetic variants associated with AIS can improve our understanding of the mechanisms of the disease, as well as assist in designing treatment methods and preventive measures.

A replication study for association of 5 single nucleotide polymorphisms with curve progression of adolescent idiopathic scoliosis in Japanese patients

STUDY DESIGN

A genetic association study of single nucleotide polymorphisms (SNPs) previously reported to be associated with curve progression of adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To determine whether the association of 5 SNPs with curve progression reported in Chinese with AIS are replicated in Japanese patients with AIS.

SUMMARY OF BACKGROUND DATA

AIS is a common spinal deformity and has a strong genetic predisposition. Predicting curve progression is important in clinical practice. The progression of AIS is reported to be associated with a number of genes. Associations with neurotrophin 3, G protein-coupled estrogen receptor, and tissue inhibitor of metalloproteinase 2 have been reported in Han Chinese with AIS; however, there has been no replication study for them.

METHODS

We recruited 2117 patients with AIS with a Cobb angle of 10° or greater of scoliosis curves. They were grouped into progression and nonprogression groups according to their scoliosis curves. Patients whose scoliotic curves were 40° or greater were included in the progression group, and those whose scoliotic curves were less than 30° and had reached skeletal maturation in the nonprogression group. We evaluated the association of 5 SNPs (rs11063714 in neurotrophin 3, rs3808351, rs10269151, and rs4266553 in G protein-coupled estrogen receptor, and rs8179090 in tissue inhibitor of metalloproteinase 2 with curve progression by comparing risk allele frequencies between the 2 groups and the mean Cobb angle for each genotype.

RESULTS

We evaluated the progression (N = 880) and nonprogression (N = 492) subjects, and their risk allele frequencies were not significantly different. The mean Cobb angle for each genotype also did not have statistical difference. We found no replication of the association on AIS curve progression in any of the SNPs.

CONCLUSION

The associations of the 5 SNPs with progression of AIS curve are not definite. Large-scale association studies based on appropriate criteria for progression would be necessary to identify SNPs associated with the curve progression.

Association between common variants near LBX1 and adolescent idiopathic scoliosis replicated in the Chinese Han population

Background

Adolescent idiopathic scoliosis (AIS) is one of the most common spinal deformities found in adolescent populations. Recently, a genome-wide association study (GWAS) in a Japanese population indicated that three single nucleotide polymorphisms (SNPs), rs11190870, rs625039 and rs11598564, all located near the LBX1 gene, may be associated with AIS susceptibility [1]. This study suggests a novel AIS predisposition candidate gene and supports the hypothesis that somatosensory functional disorders could contribute to the pathogenesis of AIS. These findings warrant replication in other populations.

Methodology/Principal Findings

First, we conducted a case-control study consisting of 953 Chinese Han individuals from southern China (513 patients and 440 healthy controls), and the three SNPs were all found to be associated with AIS predisposition. The ORs were observed as 1.49 (95% CI 1.23–1.80, P = 5.09E-5), 1.70 (95% CI 1.42–2.04, P = 1.17E-8) and 1.52 (95% CI 1.27–1.83, P = 5.54E-6) for rs625039, rs11190870 and rs11598564, respectively. Second, a case-only study including a subgroup of AIS patients (N = 234) was performed to determine the effects of these variants on the severity of the condition. However, we did not find any association between these variants and the severity of curvature.

Conclusion

This study shows that the genetic variants near the LBX1 gene are associated with AIS susceptibility in Chinese Han population. It successfully replicates the results of the GWAS, which was performed in a Japanese population.

Genetic aspects of congenital and idiopathic scoliosis

Congenital and idiopathic scoliosis represent disabling conditions of the spine. While congenital scoliosis (CS) is caused by morphogenic abnormalities in vertebral development, the cause(s) for idiopathic scoliosis is (are) likely to be varied, representing alterations in skeletal growth, neuromuscular imbalances, disturbances involving communication between the brain and spine, and others. Both conditions are characterized by phenotypic and genetic heterogeneities, which contribute to the difficulties in understanding their genetic basis that investigators face. Despite the differences between these two conditions there is observational and experimental evidence supporting common genetic mechanisms. This paper focuses on the clinical features of both CS and IS and highlights genetic and environmental factors which contribute to their occurrence. It is anticipated that emerging genetic technologies and improvements in phenotypic stratification of both conditions will facilitate improved understanding of the genetic basis for these conditions and enable targeted prevention and treatment strategies.

The genetic epidemiology of idiopathic scoliosis

Purpose

Idiopathic scoliosis is a complex developmental syndrome defined by an abnormal structural curvature of the spine. High treatment costs, chronic pain/discomfort, and the need for monitoring at-risk individuals contribute to the global healthcare burden of this musculoskeletal disease. Although many studies have endeavored to identify underlying genes, little progress has been made in understanding the etiopathogenesis. The objective of this comprehensive review was to summarize genetic associations/linkages with idiopathic scoliosis, as well as explore the strengths and weaknesses of each study, such that it may serve as a guide for the design and interpretation of future genetic studies in scoliosis.

Methods

We searched PubMed and Human Genome Epidemiology (HuGE) Navigator using the search terms “gene and scoliosis”. Linkage or association studies published in English and available full-text were further analyzed as regards results, experimental design, and statistical approach.

Results

We identified and analyzed 50 studies matching our criteria. These consisted of 34 candidate gene studies (6 linkage, 28 association) and 16 genome-wide studies [14 pedigree-based linkage, 2 genome-wide association studies (GWAS)]. Findings involved genes related to connective tissue structure, bone formation/metabolism, melatonin signaling pathways, puberty and growth, and axon guidance pathways. Variability in results between studies suggested ethnic and/or genetic heterogeneity.

Conclusions

The major difficulty in idiopathic scoliosis research is phenotypic and genetic heterogeneity. Genetic research was overrepresented by underpowered studies. The use of biological endophenotypes, as well as restricted clinical definitions, may help to partition variation and increase the power of studies to detect or confirm an effect.