Idiopathic scoliosis in twins studied by DNA fingerprinting

Association between the GLP1R A316T Mutation and Adolescent Idiopathic Scoliosis in French Canadian and Italian Cohorts

Studies have revealed anthropometric discrepancies in girls with adolescent idiopathic scoliosis (AIS) compared to non-scoliotic subjects, such as a higher stature, lower weight, and lower body mass index. While the causes are still unknown, it was proposed that metabolic hormones could play a role in AIS pathophysiology. Our objectives were to evaluate the association of GLP1R A316T polymorphism in AIS susceptibility and to study its relationship with disease severity and progression. We performed a retrospective case-control association study with controls and AIS patients from an Italian and French Canadian cohort. The GLP1R rs10305492 polymorphism was genotyped in 1025 subjects (313 non-scoliotic controls and 712 AIS patients) using a validated TaqMan allelic discrimination assay. Associations were evaluated by odds ratio and 95% confidence intervals. In the AIS group, there was a higher frequency of the variant genotype A/G (4.2% vs. 1.3%, OR = 3.40, p = 0.016) and allele A (2.1% vs. 0.6%, OR = 3.35, p = 0.017) than controls. When the AIS group was stratified for severity (≤40° vs. >40°), progression of the disease (progressor vs. non-progressor), curve type, or body mass index, there was no statistically significant difference in the distribution of the polymorphism. Our results support that the GLP1R A316T polymorphism is associated with a higher risk of developing AIS, but without being associated with disease severity and progression.

Are the Spinal Changes in the Course of Scoliogeny Primary but Secondary?

In this opinion article, there is an analysis and discussion regarding the effects of growth on the spinal and rib cage deformities, the role of the rib cage in scoliogeny, the lateral spinal profile in adolescent idiopathic scoliosis (AIS), the genetics and epigenetics of AIS, and the interesting and novel field investigating the sleep impact at nighttime on AIS in relation to the sequence of the scoliogenetic changes in scoliotics. The expressed opinions are mainly based on the published peer-reviewed research of the author and his team of co-authors. Based on the analysis noted above, it can be postulated that the vertebral growth changes in the spine during initial idiopathic scoliosis (IS) development are not primary-intrinsic but secondary changes. The primary cause starting the deformity is not located within the vertebral bodies. Instead, the deformations seen in the vertebral bodies are the secondary effects of asymmetrical loads exerted upon them, due to muscular loads, growth, and gravity.

Evidence of causality of low body mass index on risk of adolescent idiopathic scoliosis: a Mendelian randomization study

Introduction

Adolescent idiopathic scoliosis (AIS) is a disorder with a three-dimensional spinal deformity and is a common disease affecting 1-5% of adolescents. AIS is also known as a complex disease involved in environmental and genetic factors. A relation between AIS and body mass index (BMI) has been epidemiologically and genetically suggested. However, the causal relationship between AIS and BMI remains to be elucidated.

Material and methods

Mendelian randomization (MR) analysis was performed using summary statistics from genome-wide association studies (GWASs) of AIS (Japanese cohort, 5,327 cases, 73,884 controls; US cohort: 1,468 cases, 20,158 controls) and BMI (Biobank Japan: 173430 individual; meta-analysis of genetic investigation of anthropometric traits and UK Biobank: 806334 individuals; European Children cohort: 39620 individuals; Population Architecture using Genomics and Epidemiology: 49335 individuals). In MR analyses evaluating the effect of BMI on AIS, the association between BMI and AIS summary statistics was evaluated using the inverse-variance weighted (IVW) method, weighted median method, and Egger regression (MR-Egger) methods in Japanese.

Results

Significant causality of genetically decreased BMI on risk of AIS was estimated: IVW method (Estimate (beta) [SE] = -0.56 [0.16], p = 1.8 × 10-3), weighted median method (beta = -0.56 [0.18], p = 8.5 × 10-3) and MR-Egger method (beta = -1.50 [0.43], p = 4.7 × 10-3), respectively. Consistent results were also observed when using the US AIS summary statistic in three MR methods; however, no significant causality was observed when evaluating the effect of AIS on BMI.

Conclusions

Our Mendelian randomization analysis using large studies of AIS and GWAS for BMI summary statistics revealed that genetic variants contributing to low BMI have a causal effect on the onset of AIS. This result was consistent with those of epidemiological studies and would contribute to the early detection of AIS.

Genetic animal modeling for idiopathic scoliosis research: history and considerations

PURPOSE

Idiopathic scoliosis (IS) is defined as a structural lateral spinal curvature ≥ 10° in otherwise healthy children and is the most common pediatric spinal deformity. IS is known to have a strong genetic component; however, the underlying etiology is still largely unknown. Animal models have been used historically to both understand and develop treatments for human disease, including within the context of IS. This intended audience for this review is clinicians in the fields of musculoskeletal surgery and research.

METHODS

In this review article, we synthesize current literature of genetic animal models of IS and introduce considerations for researchers.

RESULTS

Due to complex genetic and unique biomechanical factors (i.e., bipedalism) hypothesized to contribute to IS in humans, scoliosis is a difficult condition to replicate in model organisms.

CONCLUSION

We advocate careful selection of animal models based on the scientific question and introduce gaps and limitations in the current literature. We advocate future research efforts to include animal models with multiple characterized genetic or environmental perturbations to reflect current understanding of the human condition.

Genetic variants associated with the occurrence and progression of adolescent idiopathic scoliosis: a systematic review protocol

BACKGROUND

Adolescent idiopathic scoliosis (AIS) is a structural lateral spinal curvature of ≥ 10° with rotation. Approximately 2-3% of children in most populations are affected with AIS, and this condition is responsible for approximately $1.1 billion in surgical costs to the US healthcare system. Although a genetic factor for AIS has been demonstrated for decades, with multiple potentially contributory loci identified across populations, treatment options have remained limited to bracing and surgery.

METHODS

The databases MEDLINE (via PubMed), Embase, Google Scholar, and Ovid MEDLINE will be searched and limited to articles in English. We will conduct title and abstract, full-text, and data extraction screening through Covidence, followed by data transfer to a custom REDCap database. Quality assessment will be confirmed by multiple reviewers. Studies containing variant-level data (i.e., GWAS, exome sequencing) for AIS subjects and controls will be considered. Outcomes of interest will include presence/absence of AIS, scoliosis curve severity, scoliosis curve progression, and presence/absence of nucleotide-level variants. Analyses will include odds ratios and relative risk assessments, and subgroup analysis (i.e., males vs. females, age groups) may be applied. Quality assessment tools will include GRADE and Q-Genie for genetic studies.

DISCUSSION

In this systematic review, we seek to evaluate the quality of genetic evidence for AIS to better inform research efforts, to ultimately improve the quality of patient care and diagnosis.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO registration #CRD42021243253.

Idiopathic scoliosis: a systematic review and meta-analysis of heritability

Purpose

Methods

Results

Conclusion

Polygenic Risk Score of Adolescent Idiopathic Scoliosis for Potential Clinical Use

Adolescent idiopathic scoliosis (AIS) is a common disease causing three-dimensional spinal deformity in as many as 3% of adolescents. Development of a method that can accurately predict the onset and progression of AIS is an immediate need for clinical practice. Because the heritability of AIS is estimated as high as 87.5% in twin studies, prediction of its onset and progression based on genetic data is a promising option. We show the usefulness of polygenic risk score (PRS) for the prediction of onset and progression of AIS. We used AIS genomewide association study (GWAS) data comprising 79,211 subjects in three cohorts and constructed a PRS based on association statistics in a discovery set including 31,999 female subjects. After calibration using a validation data set, we applied the PRS to a test data set. By integrating functional annotations showing heritability enrichment in the selection of variants, the PRS demonstrated an association with AIS susceptibility (p = 3.5 × 10^-40 with area under the receiver-operating characteristic [AUROC] = 0.674, sensitivity = 0.644, and specificity = 0.622). The decile with the highest PRS showed an odds ratio of as high as 3.36 (p = 1.4 × 10^-10 ) to develop AIS compared with the fifth in decile. The addition of a predictive model with only a single clinical parameter (body mass index) improved predictive ability for development of AIS (AUROC = 0.722, net reclassification improvement [NRI] 0.505 ± 0.054, p = 1.6 × 10^-8 ), potentiating clinical use of the prediction model. Furthermore, we found the Cobb angle (CA), the severity measurement of AIS, to be a polygenic trait that showed a significant genetic correlation with AIS susceptibility (rg = 0.6, p = 3.0 × 10^-4 ). The AIS PRS demonstrated a significant association with CA. These results indicate a shared polygenic architecture between onset and progression of AIS and the potential usefulness of PRS in clinical settings as a predictor to promote early intervention of AIS and avoid invasive surgery. © 2021 American Society for Bone and Mineral Research (ASBMR).

A Decade in Review after Idiopathic Scoliosis Was First Called a Complex Trait-A Tribute to the Late Dr. Yves Cotrel for His Support in Studies of Etiology of Scoliosis

Adolescent Idiopathic Scoliosis (AIS) is a prevalent and important spine disorder in the pediatric age group. An increased family tendency was observed for a long time, but the underlying genetic mechanism was uncertain. In 1999, Dr. Yves Cotrel founded the Cotrel Foundation in the Institut de France, which supported collaboration of international researchers to work together to better understand the etiology of AIS. This new concept of AIS as a complex trait evolved in this setting among researchers who joined the annual Cotrel meetings. It is now over a decade since the first proposal of the complex trait genetic model for AIS. Here, we review in detail the vast information about the genetic and environmental factors in AIS pathogenesis gathered to date. More importantly, new insights into AIS etiology were brought to us through new research data under the perspective of a complex trait. Hopefully, future research directions may lead to better management of AIS, which has a tremendous impact on affected adolescents in terms of both physical growth and psychological development.

Genetic Variants of CHD7 Are Associated with Adolescent Idiopathic Scoliosis

STUDY DESIGN

A case-control association study.

OBJECTIVES

The aim of this study was to investigate whether CHD7 was associated with adolescent idiopathic scoliosis in Chinese Han population and to further explore the functional role of CHD7 in the development of adolescent idiopathic scoliosis (AIS).

SUMMARY OF BACKGROUND DATA

Several studies have explored the association of CHD7 with scoliosis in patients of European descent, while the results were inconsistent. There was a lack of study investigating the association of CHD7 with AIS in Chinese Han population.

METHODS

Variants within CHD7 were genotyped in 965 AIS patients and 976 healthy controls. Whole exome sequencing was performed in 96 AIS patients. Paraspinal muscles of 43AIS patients and 38 lumbar disc herniation patients were collected for the evaluation of the gene expression. Intergroup comparison was performed with the χ2 test for genotyping data or Student t test for tissue expression. The relationship of CHD7 expression with clinical phenotypes was determined by the Pearson correlation.

RESULT

Variant rs121434341 of CHD7 was significantly associated with AIS. AIS patients were found to have a remarkable higher frequency of allele G when compared with healthy controls (2.89% vs. 1.57%, P = 0.0018), with an odds ratio value of 1.89. A pathogenic mutation affecting normal splicing was identified in a patient. Moreover, the expression level of CHD7 in AIS patients was significantly lower than in the controls (0.0008437 ± 0.00004583 vs. 0.001129 ± 0.00003773, P < 0.001), and CHD7 expression was positively correlated with bone mineral contents (P = 0.036, r = 0.32).

CONCLUSION

Genetic variants of CHD7 were significantly associated with AIS. Moreover, the decreased expression of CHD7 may be involved in the abnormal bone mass of AIS patients. Further studies are warranted to investigate the functional role of CHD7 in the pathogenesis of AIS.Level of Evidence: 3.

Novel Mutations in UTS2R are Associated with Adolescent Idiopathic Scoliosis in the Chinese Population

STUDY DESIGN

A case-control study.

OBJECTIVES

To investigate the association of urotensin II (UTS2) signals with the susceptibility of adolescent idiopathic scoliosis (AIS) in the Chinese Han population.

SUMMARY OF BACKGROUND DATA

Dysregulated UTS2 signals induced by impaired cerebrospinal fluid flow have been implicated in the development of idiopathic scoliosis through studies on zebrafish. Furthermore, mutations in urotensin II receptor (UTS2R) were reported to cause severe scoliosis in zebrafish. In spite of the evidence presented in animal models, there is still a lack of knowledge concerning the role of UTS2 signaling related genes in AIS.

METHODS

In the discovery stage, exons of UTS2, UTS2R, and UTS2D were sequenced for 200 AIS patients and 200 healthy controls. Newly identified mutations were further genotyped in another independent cohort of 1000 AIS patients and 1000 controls by allelic-specific multiple ligase detection reactions. Gene expression analysis was performed in 36 AIS patients and 36 age-matched congenital scoliosis patients. The Chi-square test was used to compare the genotyping data between the groups. Gene expression analysis was compared with the Student t test.

RESULTS

Association between two novel mutations (rs11654140, c.51T > C; rs568196624, c.1146C > G) and the development of AIS was identified. Allele C of rs11654140 and allele G of rs568196624 were significantly associated with the risk of AIS (1.5% vs. 0.5%, odds ratio = 3.02, P = 0.01 for rs11654140; 1.41% vs. 0.58%, odds ratio = 2.29, P = 0.04 for rs568196624). The mRNA expression of UTS2R in the AIS group was significantly higher as compared with that in the control group (0.059 ± 0.015 vs. 0.035 ± 0.013, P < 0.01).

CONCLUSIONS

Rare mutations in UTS2R were significantly associated with AIS. Expression of UTS2R was significantly increased in AIS patients. The role of UTS2 signaling in the development of AIS is worthy of further investigation.Level of Evidence: N/A.

The heritability of coronal and sagittal phenotype in idiopathic scoliosis: a report of 12 monozygotic twin pairs

PURPOSE

One of the pathways through which genetics may act in the causation of idiopathic scoliosis is inheritance of a specific sagittal profile that predisposes for its development. In this study, coronal and sagittal parameters were compared in an international collection of monozygotic twins with idiopathic scoliosis.

METHODS

Twelve monozygotic twin pairs who underwent biplanar radiography for idiopathic scoliosis were systematically identified in existing scoliosis databases in The Netherlands, Sweden, and Denmark. On the first available radiographs, the coronal and sagittal curve parameters (Roussouly and Abelin types, thoracic kyphosis, lumbar lordosis and length of the posteriorly inclined segment) were determined.

RESULTS

In all 12 monozygotic twin pairs, both twins were affected by AIS. Four (33%) twin pairs had similar coronal and sagittal spinal phenotype, whereas two (17%) had different coronal phenotype and similar sagittal profiles, and six (50%) pairs had different coronal as well as sagittal phenotype.

CONCLUSIONS

Analysis of biplanar curve characteristics in monozygotic twins showed that all twin pairs were affected by idiopathic scoliosis. However, only 33% of the pairs had similar coronal and sagittal spinal phenotypes. Based on this limited dataset, the hypothesis can be formulated that besides genetic pre-disposition, the individual (inherited) sagittal profile plays a role in the development of different coronal curve type.

Dietary Habits Had No Relationship with Adolescent Idiopathic Scoliosis: Analysis Utilizing Quantitative Data about Dietary Intakes

Although several genetic and environmental factors have been identified as risk factors of adolescent idiopathic scoliosis (AIS), the influence of dietary intake has not been elucidated. We evaluated the association between AIS and dietary habits among female students. Junior high school girls aged 12 to 15 years in the Tokyo metropolitan area who underwent a second school screening for scoliosis were recruited. AIS was diagnosed by orthopedic surgeons specializing in scoliosis, using standing whole spine radiography. Students with a Cobb angle of ≥15° were classified into the AIS group, and others were considered healthy controls. Dietary assessment was performed using a validated diet history questionnaire. Dietary intakes were categorized into quintiles based on distribution, and crude and multivariable odds ratios and 95% confidence intervals for AIS for each quintile category of dietary variable were calculated, with the lowest quintile category used as a reference. In total, 2431 subjects were included in the analysis, and 47.8% of them were diagnosed with AIS. None of the selected nutrients or food groups was significantly associated with AIS. In conclusion, dietary habits may not be associated with AIS.

An N-Ethyl-N-Nitrosourea (ENU) Mutagenized Mouse Model for Autosomal Dominant Nonsyndromic Kyphoscoliosis Due to Vertebral Fusion

Kyphosis and scoliosis are common spinal disorders that occur as part of complex syndromes or as nonsyndromic, idiopathic diseases. Familial and twin studies implicate genetic involvement, although the causative genes for idiopathic kyphoscoliosis remain to be identified. To facilitate these studies, we investigated progeny of mice treated with the chemical mutagen N-ethyl-N-nitrosourea (ENU) and assessed them for morphological and radiographic abnormalities. This identified a mouse with kyphoscoliosis due to fused lumbar vertebrae, which was inherited as an autosomal dominant trait; the phenotype was designated as hereditary vertebral fusion (HVF) and the locus as Hvf. Micro-computed tomography (μCT) analysis confirmed the occurrence of nonsyndromic kyphoscoliosis due to fusion of lumbar vertebrae in HVF mice, consistent with a pattern of blocked vertebrae due to failure of segmentation. μCT scans also showed the lumbar vertebral column of HVF mice to have generalized disc narrowing, displacement with compression of the neural spine, and distorted transverse processes. Histology of lumbar vertebrae revealed HVF mice to have irregularly shaped vertebral bodies and displacement of intervertebral discs and ossification centers. Genetic mapping using a panel of single nucleotide polymorphic (SNP) loci arranged in chromosome sets and DNA samples from 23 HVF (eight males and 15 females) mice, localized Hvf to chromosome 4A3 and within a 5-megabase (Mb) region containing nine protein coding genes, two processed transcripts, three microRNAs, five small nuclear RNAs, three large intergenic noncoding RNAs, and 24 pseudogenes. However, genome sequence analysis in this interval did not identify any abnormalities in the coding exons, or exon-intron boundaries of any of these genes. Thus, our studies have established a mouse model for a monogenic form of nonsyndromic kyphoscoliosis due to fusion of lumbar vertebrae, and further identification of the underlying genetic defect will help elucidate the molecular mechanisms involved in kyphoscoliosis. © 2018 The Authors. JBMR Plus is published by Wiley Periodicals, Inc. on behalf of the American Society for Bone and Mineral Research.

Physical Activities and Lifestyle Factors Related to Adolescent Idiopathic Scoliosis

BACKGROUND

In addition to genetic factors, environmental and lifestyle factors are thought to play an important role in the onset of adolescent idiopathic scoliosis (AIS). This cross-sectional study was conducted to explore lifestyle factors related to AIS.

METHODS

This study included 2,759 Japanese female junior high school students who planned a secondary screening after an initial moiré topography screening indicated possible scoliosis. The students and their mothers, or guardians, were asked to fill out a questionnaire consisting of 38 questions about demographic factors, lifestyle-related factors, social factors, household environment, participation in sports, health status, and factors related to the mother's pregnancy and delivery. The questionnaire was completed by 2,747 students (a 99.6% response rate). After excluding students with heart disease, neurological disease, or a congenital vertebral anomaly, 2,600 students were eligible for assessment. After undergoing a secondary screening with standing radiographs of the spine, students were assigned to the normal (control) group if radiographs showed a curve of <15° or to the scoliosis group if they had a curve of ≥15°. The odds ratios (ORs) for AIS in relation to the possible risk or preventive factors were estimated by logistic regression analyses.

RESULTS

No lifestyle-related factor was significantly associated with AIS. However, AIS was associated with classical ballet training (OR, 1.38; 95% confidence interval [CI], 1.09 to 1.75); the odds of AIS developing increased as the child's frequency of training, number of years of experience, and duration of training in ballet increased. The OR for AIS was 1.5 times higher for participants whose mothers had scoliosis. AIS was also associated with a low body mass index (BMI). These associations remained even after mutual adjustment was performed.

CONCLUSIONS

No association was found between AIS and lifestyle-related factors. However, classical ballet training, a family history of scoliosis, and low BMI may be associated with AIS.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.

Concordance Rates of Adolescent Idiopathic Scoliosis in a Danish Twin Population

STUDY DESIGN

Clinical, radiological, and genetic determination of zygosity of twin pairs from the Danish Twin Registry who self-reported having adolescent idiopathic scoliosis (AIS).

OBJECTIVE

To establish concordance rates of AIS.

SUMMARY OF BACKGROUND DATA

The etiology of and the true mode of inheritance of AIS remain unclear. Studies on concordance in twin pairs provide a basis for analyzing the influence of genetic versus environmental factors. In 2007, using self-report of AIS from the Danish Twin Registry, concordance rates of 0.13 in monozygotic twins and 0.00 in dizygotic twins were reported.

METHODS

All 46,418 twins registered in the Danish Twin Registry born from 1931 to 1982 were sent a survey, which included questions about scoliosis. The survey was returned by 34,944 individuals (75.3%) representing 23,204 pairs. From the present study, 548 individuals representing 274 complete twin pairs in which at least one twin self-reported having scoliosis were invited to a clinical and radiological examination. Zygosity was established by genetic testing.

RESULTS

A total of 182 individuals (33.2%) of the original cohort agreed to participate, 128 of whom had scoliosis by self-report. There were 91 twin pairs, in which one or both twins had reported scoliosis and 36 individuals whose twin did not want to participate. Only 35 (27%) of the 128 participants with self-reported scoliosis had a clinically and radiologically confirmed curve. Calculating concordance in twins with Cobb angles greater than 10°, we found that the pairwise concordance rate was 0.4 (0.10-0.70) for monozygotic and 0.05 (-0.05-0.15) for dizygotic twins, P = 0.05, probandwise concordance was 0.45 (0.16-0.74) for monozygotic and 0.1 (-0.03-0.23) for dizygotic pairs.

CONCLUSION

Concordance rates in a Danish twin population using genetic testing for zygosity are higher than previously reported using self-report. Although not statistically significant, the differences in monozygotic and dizygotic pairs indicate that genetic factors may be of importance for scoliosis.

LEVEL OF EVIDENCE

3.

Exome sequencing identifies a rare HSPG2 variant associated with familial idiopathic scoliosis

Idiopathic scoliosis occurs in 3% of individuals and has an unknown etiology. The objective of this study was to identify rare variants that contribute to the etiology of idiopathic scoliosis by using exome sequencing in a multigenerational family with idiopathic scoliosis. Exome sequencing was completed for three members of this multigenerational family with idiopathic scoliosis, resulting in the identification of a variant in the HSPG2 gene as a potential contributor to the phenotype. The HSPG2 gene was sequenced in a separate cohort of 100 unrelated individuals affected with idiopathic scoliosis and also was examined in an independent idiopathic scoliosis population. The exome sequencing and subsequent bioinformatics filtering resulted in 16 potentially damaging and rare coding variants. One of these variants, p.Asn786Ser, is located in the HSPG2 gene. The variant p.Asn786Ser also is overrepresented in a larger cohort of idiopathic scoliosis cases compared with a control population (P = 0.024). Furthermore, we identified additional rare HSPG2 variants that are predicted to be damaging in two independent cohorts of individuals with idiopathic scoliosis. The HSPG2 gene encodes for a ubiquitous multifunctional protein within the extracellular matrix in which loss of function mutation are known to result in a musculoskeletal phenotype in both mouse and humans. Based on these results, we conclude that rare variants in the HSPG2 gene potentially contribute to the idiopathic scoliosis phenotype in a subset of patients with idiopathic scoliosis. Further studies must be completed to confirm the effect of the HSPG2 gene on the idiopathic scoliosis phenotype.

Lack of association between adolescent idiopathic scoliosis and previously reported single nucleotide polymorphisms in MATN1, MTNR1B, TPH1, and IGF1 in a Japanese population

Adolescent idiopathic scoliosis (AIS) is a spinal deformity most commonly arising in apparently healthy girls around puberty. AIS has a strong genetic predisposition. Several genetic associations between AIS and single nucleotide polymorphisms (SNPs) have been reported; common SNPs in the genes for matrilin 1 (MATN1), melatonin receptor 1B (MTNR1B), tryptophan hydroxylase 1 (TPH1), and insulin-like growth factor 1 (IGF1) are reported to be associated with AIS in Chinese. However, these associations have not been replicated so far. To confirm the associations, we compared these SNPs with AIS predisposition and curve severity in a population of Japanese females consisting of 798 AIS patients and 1,239 controls. All the subjects were genotyped using the PCR-based Invader assay. We found no association of any of the SNPs with AIS predisposition or curve severity. Considering the statistical power and sample size of the present study, we concluded that these SNPs are not associated with either AIS predisposition or curve severity in Japanese.

Genetics of scoliosis

Scoliosis is one of the oldest known deformities of humankind; however, the cause still remains ill defined. Although there is a lack of uniform agreement on the inclusion criteria for the definition of scoliosis, most investigators agree that a coronal curve must measure at least 10 degrees for the patient to be considered to have scoliosis. A broad range of articles were reviewed and the relevant publications that contributed information regarding the genetics of scoliosis were selected for inclusion in this report. Based on family pedigree and genetic studies, the proposed pattern of inheritance for markers of scoliosis are expected to be autosomal dominant, X-linked, multigene, or multifactorial. This is further complicated by locus heterogeneity, allele heterogeneity, and carrier states found in normal individuals. Although none of these modes of inheritance has been definitively proven, it appears that a multifactorial mode of inheritance with variable penetrance is the most likely method.

Familial relationships of normal spine shape

Familial correlations in the spinal shape of children are explored using statistical shape analysis. Measurements of the spine on the surface of the back were taken using an optical device, and recorded for several hundred children from the Leeds area of the U.K. A portion of the spine from the distal thoracic to proximal lumbar spine was used for the analysis, and measures of the shape of the spine line were determined using Procrustes analysis and principal components (PCs) analysis. Analysis was carried out on scans repeated in triplicate and scans taken six months apart, and good repeatability was demonstrated. Four groups of children were considered in the main study: monozygotic twins, dizygotic twins, same sex siblings and different sex siblings. Intra-familial correlations were calculated for the shape measures, and also for age and sex matched unrelated controls. The second PC score (which measures possible lordosis) had significant positive correlation in the family groups. It was observed that the familial correlations were higher for the genetically closer groups. Also, the same sex siblings had higher correlation than the different sex siblings. All sibling groups showed greater correlation of sagittal profile for the second PC score than unrelated controls. A significant correlation was observed in same sex pairings for the control data. This work suggests that some elements of spinal profile may be familial but also shows correlation with sex. Both of these observations may be important in the aetiology of idiopathic scoliosis.

Genetic association of complex traits: using idiopathic scoliosis as an example

Although the exact etiology of adolescent idiopathic scoliosis is still undefined, genetic factors play an important role. Some patients have familial genetic disease that appears to have an autosomal dominant pattern. Linkage studies of these families revealed multiple potential genetic loci that may predispose individuals to the condition. Additional genetic analysis is required to identify the disease-predisposition genes of the loci found in the linkage studies. The initial localization of potential critical loci through large family-based population studies now needs fine mapping by association studies using high-density polymorphic markers (single nucleotide polymorphisms or SNPs). These markers are now available as a result of the Human Genome Project, International HapMap Project, and other genetic diversity projects. The application of this emerging data in a large association study of affected individuals and controls is integral for the identification of putative genes. With these complementary approaches, we will be able to progress with mutational analysis of hopefully a small set of candidate genes in the near future. In this commentary, we illustrate what is possible in the genomic era, and indicate what we should expect from genetic studies in adolescent idiopathic scoliosis, a complex trait disease.