Polygenic inheritance of adolescent idiopathic scoliosis: A study of extended families in Utah

Rare variants in FBN1 and FBN2 are associated with severe adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) causes spinal deformity in 3% of children. Despite a strong genetic basis, few genes have been associated with AIS and the pathogenesis remains poorly understood. In a genome-wide rare variant burden analysis using exome sequence data, we identified fibrillin-1 (FBN1) as the most significantly associated gene with AIS. Based on these results, FBN1 and a related gene, fibrillin-2 (FBN2), were sequenced in a total of 852 AIS cases and 669 controls. In individuals of European ancestry, rare variants in FBN1 and FBN2 were enriched in severely affected AIS cases (7.6%) compared with in-house controls (2.4%) (OR = 3.5, P = 5.46 × 10(-4)) and Exome Sequencing Project controls (2.3%) (OR = 3.5, P = 1.48 × 10(-6)). Scoliosis severity in AIS cases was associated with FBN1 and FBN2 rare variants (P = 0.0012) and replicated in an independent Han Chinese cohort (P = 0.0376), suggesting that rare variants may be useful as predictors of curve progression. Clinical evaluations revealed that the majority of AIS cases with rare FBN1 variants do not meet diagnostic criteria for Marfan syndrome, though variants are associated with tall stature (P = 0.0035) and upregulation of the transforming growth factor beta pathway. Overall, these results expand our definition of fibrillin-related disorders to include AIS and open up new strategies for diagnosing and treating severe AIS.

Scoliosis and vertebral anomalies: additional abnormal phenotypes associated with chromosome 16p11.2 rearrangement

The typical chromosome 16p11.2 rearrangements are estimated to occur at a frequency of approximately 0.6% of all samples tested clinically and have been identified as a major cause of autism spectrum disorders, developmental delay, behavioral abnormalities, and seizures. Careful examination of patients with these rearrangements revealed association with abnormal head size, obesity, dysmorphism, and congenital abnormalities. In this report, we extend this list of phenotypic abnormalities to include scoliosis and vertebral anomalies. We present detailed characterization of phenotypic and radiological data of 10 new patients, nine with the 16p11.2 deletion and one with the duplication within the coordinates chr16:29,366,195 and 30,306,956 (hg19) with a minimal size of 555 kb. We discuss the phenotypical and radiological findings in our patients and review 5 previously reported patients with 16p11.2 rearrangement and similar skeletal abnormalities. Our data suggest that patients with the recurrent 16p11.2 rearrangement have increased incidence of scoliosis and vertebral anomalies. However, additional studies are required to confirm this observation and to establish the incidence of these anomalies. We discuss the potential implications of our findings on the diagnosis, surveillance and genetic counseling of patients with 16p11.2 rearrangement.

Family history and its association to curve size and treatment in 1,463 patients with idiopathic scoliosis

PURPOSE

To study family history in relation to curve severity, gender, age at diagnosis and treatment in idiopathic scoliosis.

METHODS

A self-assessment questionnaire on family history of scoliosis was administered to 1,463 untreated, brace or surgically treated idiopathic scoliosis patients.

RESULTS

Out of the 1,463 patients, 51 % had one or more relatives with scoliosis. There was no significant difference between females and males, nor between juvenile and adolescent study participants in this respect (p = 0.939 and 0.110, respectively). There was a significant difference in maximum curve size between patients with one or more relatives with scoliosis (median 35°, interquartile range 25) and patients without any relative with scoliosis (median 32°, interquartile range 23) (p = 0.022). When stratifying patients according to treatment (observation, brace treatment or surgery), we found that it was more common to have a relative with scoliosis among the treated patients (p = 0.011). The OR for being treated was 1.32 (95% CI 1.06-1.64) when the patient had a relative with scoliosis, compared to not having.

CONCLUSIONS

Larger curve sizes were found in patients with a family history of scoliosis than in the ones without. No relation between family history and gender or between family history and age at onset of idiopathic scoliosis was found. Although the presence of a family history of scoliosis may not be a strong prognostic risk factor, it indicates that these patients are at higher risk of developing a more severe curve.

Genetic variants in GPR126 are associated with adolescent idiopathic scoliosis

Adolescent idiopathic scoliosis (AIS) is the most common pediatric skeletal disease. We previously reported a locus on chromosome 10q24.31 associated with AIS susceptibility in Japanese using a genome-wide association study (GWAS) consisting of 1,033 cases and 1,473 controls. To identify additional AIS-associated loci, we expanded the study by adding X-chromosome SNPs in the GWAS and increasing the size of the replication cohorts. Through a stepwise association study including 1,819 cases and 25,939 controls, we identified a new susceptibility locus on chromosome 6q24.1 in Japanese (P = 2.25 × 10(-10); odds ratio (OR) = 1.28). The most significantly associated SNP, rs6570507, was in GPR126 (encoding G protein-coupled receptor 126). Its association was replicated in Han Chinese and European-ancestry populations (combined P = 1.27 × 10(-14); OR = 1.27). GPR126 was highly expressed in cartilage, and the knockdown of gpr126 in zebrafish caused delayed ossification of the developing spine. Our results should provide insights into the etiology and pathogenesis of AIS.

Analysis of single nucleotide polymorphism in adolescent idiopathic scoliosis in Korea: for personalized treatment

PURPOSE

The incidence of adolescent idiopathic scoliosis (AIS) has rapidly increased, and with it, physician consultations and expenditures (about one and a half times) in the last 5 years. Recent etiological studies reveal that AIS is a complex genetic disorder that results from the interaction of multiple gene loci and the environment. For personalized treatment of AIS, a tool that can accurately measure the progression of Cobb's angle would be of great use. Gene analysis utilizing single nucleotide polymorphism (SNP) has been developed as a diagnostic tool for use in Caucasians but not Koreans. Therefore, we attempted to reveal AIS-related genes and their relevance in Koreans, exploring the potential use of gene analysis as a diagnostic tool for personalized treatment of AIS therein.

MATERIALS AND METHODS

A total of 68 Korean AIS and 35 age- and sex-matched, healthy adolescents were enrolled in this study and were examined for 10 candidate scoliosis gene SNPs.

RESULTS

This study revealed that the SNPs of rs2449539 in lysosomal-associated transmembrane protein 4 beta (LAPTM4B) and rs5742612 in upstream and insulin-like growth factor 1 (IGF1) were associated with both susceptibility to and curve severity in AIS. The results suggested that both LAPTM4B and IGF1 genes were important in AIS predisposition and progression.

CONCLUSION

Thus, on the basis of this study, if more SNPs or candidate genes are studied in a larger population in Korea, personalized treatment of Korean AIS patients might become a possibility.

Vitamin D receptor gene (VDR) transcripts in bone, cartilage, muscles and blood and microarray analysis of vitamin D responsive genes expression in paravertebral muscles of juvenile and adolescent idiopathic scoliosis patients

BACKGROUND

VDR may be considered as a candidate gene potentially related to idiopathic scoliosis susceptibility and natural history. Transcriptional profile of VDR mRNA isoforms might be changed in the structural tissues of the scoliotic spine and potentially influence the expression of VDR responsive genes. The purpose of the study was to determine differences in mRNA abundance of VDR isoforms in bone, cartilage and paravertebral muscles between tissues from curve concavity and convexity, between JIS and AIS and to identify VDR responsive genes differentiating juvenile and adolescent idiopathic scoliosis in paravertebral muscles.

METHODS

In a group of 29 patients with JIS and AIS, specimens of bone, cartilage, paravertebral muscles were harvested at the both sides of the curve apex together with peripheral blood samples. Extracted total RNA served as a matrix for VDRs and VDRl mRNA quantification by QRT PCR. Subsequent microarray analysis of paravertebral muscular tissue samples was performed with HG U133A chips (Affymetrix). Quantitative data were compared by a nonparametric Mann Whitney U test. Microarray results were analyzed with GeneSpring 11GX application. Matrix plot of normalized log-intensities visualized the degree of differentiation between muscular tissue transcriptomes of JIS and AIS group. Fold Change Analysis with cutoff of Fold Change ≥2 identified differentially expressed VDR responsive genes in paravertebral muscles of JIS and AIS.

RESULTS

No significant differences in transcript abundance of VDR isoforms between tissues of the curve concavity and convexity were found. Statistically significant difference between JIS and AIS group in mRNA abundance of VDRl isoform was found in paravertebral muscles of curve concavity. Higher degree of muscular transcriptome differentiation between curve concavity and convexity was visualized in JIS group. In paravertebral muscles Tob2 and MED13 were selected as genes differentially expressed in JIS and AIS group.

CONCLUSIONS

In Idiopathic Scolioses transcriptional activity and alternative splicing of VDR mRNA in osseous, cartilaginous, and paravertebral muscular tissues are tissue specific and equal on both sides of the curve. The number of mRNA copies of VDRl izoform in concave paravertebral muscles might be one of the factors differentiating JIS and AIS. In paravertebral muscles Tob2 and Med13 genes differentiate Adolescent and Juvenile type of Idiopathic Scoliosis.

Genetic epidemiology and heritability of AIS: A study of 415 Chinese female patients

Recent familial segregation studies supported a multifactorial genetic model for the etiology of adolescent idiopathic scoliosis (AIS). However, the extent of quantitative genetic effects, such as heritability, have not been fully evaluated. This genetic epidemiology study examined the sibling recurrent risk and heritability of AIS in first-degree relatives of 415 Chinese female patients, which is up to now the largest cohort. They were first diagnosed by community screening program and compared to 203 age-matched normal controls. Out of the total 531 sibs of AIS cases, 94 sibs had scoliosis (sibling recurrence risk = 17.7%). The prevalence of AIS among male and female sibs of an index case were 11.5% (95% CI = 7.5-15.5) and 23.0% (95% CI = 18.1-27.9), respectively. Female sibs of an index case had an increased risk of 8.9-fold (95% CI = 3.2-34.4) for developing AIS. These recurrent risks were significantly higher than the risk in the control group (p < 0.0001). Overall, heritability was estimated to be 87.5 ± 11.1%. The results confirmed the prevailing impression of strong genetic influence on the risk of AIS. Here we provided a large-scale study for the genetic aggregation estimates in an Asian population for the first time. The finding also positioned AIS among other common disease or complex traits with a high heritability.

Polygenic threshold model with sex dimorphism in adolescent idiopathic scoliosis: the Carter effect

BACKGROUND

Adolescent idiopathic scoliosis occurs between two and ten times more frequently in females than in males. The exact cause of this sex discrepancy is unknown, but it may represent a difference in susceptibility to the deformity. If this difference is attributable to genetic factors, then males with adolescent idiopathic scoliosis would need to inherit a greater number of susceptibility genes compared with females to develop the deformity. Males would also be more likely to transmit the disease to their children and to have siblings with adolescent idiopathic scoliosis. Such a phenomenon is known as the Carter effect, and the presence of such an effect would support a multifactorial threshold model of inheritance.

METHODS

One hundred and forty multiplex families in which more than one individual was affected with adolescent idiopathic scoliosis were studied. These families contained 1616 individuals, including 474 individuals with adolescent idiopathic scoliosis and 1142 unaffected relatives. The rates of transmission from the 122 affected mothers and from the twenty-eight affected fathers were calculated, and the prevalence among siblings was determined in the nuclear families of affected individuals.

RESULTS

The prevalence of adolescent idiopathic scoliosis in these multiplex families was lowest in sons of affected mothers (36%, thirty-eight of 105) and highest in daughters of affected fathers (85%, twenty-two of twenty-six). Affected fathers transmitted adolescent idiopathic scoliosis to 80% (thirty-seven) of forty-six children, whereas affected mothers transmitted it to 56% (133) of 239 children (p < 0.001). Siblings of affected males also had a significantly higher prevalence of adolescent idiopathic scoliosis (55%, sixty-one of 110) compared with siblings of affected females (45%, 206 of 462) (p = 0.04).

CONCLUSIONS

This study demonstrates the presence of the Carter effect in adolescent idiopathic scoliosis. This pattern can be explained by polygenic inheritance of adolescent idiopathic scoliosis, with a greater genetic load required for males to be affected.

Heritability of scoliosis

PURPOSE

To estimate the heritability of scoliosis in the Swedish Twin Registry.

METHODS

Self-reported data on scoliosis from 64,578 twins in the Swedish Twin Registry were analysed. Prevalence, pair- and probandwise concordances and tetrachoric correlations in mono- and dizygotic same-sex twins were calculated. The relative importance of genetic variance, i.e. the heritability, and unique and shared environmental variance was estimated using structural equation modelling in Mx software. In addition, all twins in the twin registry were matched against the Swedish Inpatient Register on the primary diagnosis idiopathic scoliosis.

RESULTS

The prevalence of scoliosis was 4%. Pair- and probandwise concordance was 0.11/0.17 for mono- and 0.04/0.08 for same-sex dizygotic twins. The tetrachoric correlation (95% CI) was 0.41 (0.33-0.49) in mono- and 0.18 (0.09-0.29) in dizygotic twins. The most favourable model in the Mx analyses estimated the additive genetic effects (95% CI) to 0.38 (0.18-0.46) and the unique environmental effects to 0.62 (0.54-0.70). Shared environmental effects were not significant. The pairwise/probandwise concordance for idiopathic scoliosis in the Swedish Inpatient Register was 0.08/0.15 for monozygotic and zero/zero for same-sex dizygotic twins.

CONCLUSION

Using self-reported data on scoliosis from the Swedish Twin Registry, we estimate that 38% of the variance in the liability to develop scoliosis is due to additive genetic effects and 62% to unique environmental effects. This is the first study of sufficient size to make heritability estimates of scoliosis.

Differential proteome analysis of bone marrow mesenchymal stem cells from adolescent idiopathic scoliosis patients

Adolescent idiopathic scoliosis (AIS) is a complex three-dimensional deformity of the spine. The cause and pathogenesis of scoliosis and the accompanying generalized osteopenia remain unclear despite decades of extensive research. In this study, we utilized two-dimensional fluorescence difference gel electrophoresis (2D-DIGE) coupled with mass spectrometry (MS) to analyze the differential proteome of bone marrow mesenchymal stem cells (BM-MSCs) from AIS patients. In total, 41 significantly altered protein spots were detected, of which 34 spots were identified by MALDI-TOF/TOF analysis and found to represent 25 distinct gene products. Among these proteins, five related to bone growth and development, including pyruvate kinase M2, annexin A2, heat shock 27 kDa protein, γ-actin, and β-actin, were found to be dysregulated and therefore selected for further validation by Western blot analysis. At the protein level, our results supported the previous hypothesis that decreased osteogenic differentiation ability of MSCs is one of the mechanisms leading to osteopenia in AIS. In summary, we analyzed the differential BM-MSCs proteome of AIS patients for the first time, which may help to elucidate the underlying molecular mechanisms of bone loss in AIS and also increase understanding of the etiology and pathogenesis of AIS.

Validation of DNA-based prognostic testing to predict spinal curve progression in adolescent idiopathic scoliosis

STUDY DESIGN

Validation of a prognostic DNA marker panel.

OBJECTIVE

The goals of this study were to develop and test the negative predictive value of a prognostic DNA test for adolescent idiopathic scoliosis (AIS) and to establish clinically meaningful endpoints for the test.

SUMMARY OF BACKGROUND DATA

Clinical features do not adequately predict which children diagnosed with minimal or mild AIS will have the progressive form of the disease; genetic markers associated with curve progression might offer clinically useful prognostic insights.

METHODS

Logistic regression was used to develop an algorithm to predict spinal curve progression incorporating genotypes for 53 single nucleotide polymorphisms and the patient's presenting spinal curve (Cobb angle). Three cohorts with known AIS outcomes were selected to reflect intended-use populations with various rates of AIS progression: 277 low-risk females representing a screening cohort, 257 females representing higher risk patients followed at referral centers, and 163 high risk males. DNA was extracted from saliva, and genotypes were determined using TaqMan assays. AIS Prognostic Test scores ranging from 1 to 200 were calculated.

RESULTS

Low-risk scores (<41) had negative predictive values of 100%, 99%, and 97%, respectively, in the tested populations. In the risk model, we used cutoff scores of 50 and 180 to identify 75% of patients as low-risk (<1% risk of progressing to a surgical curve), 24% as intermediate-risk, and 1% as high-risk.

CONCLUSION

Prognostic testing for AIS has the potential to reduce psychological trauma, serial exposure to diagnostic radiation, unnecessary treatments, and direct and indirect costs-of-care related to scoliosis monitoring in low-risk patients. Further improvements in test performance are expected as the optimal markers for each locus are identified and the underlying biologic pathways are better understood. The validity of the test applies only to white AIS patients; versions of the test optimized for AIS patients of other races have yet to be developed.