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.
Drosophila Nipped-B is an essential protein that has multiple functions. It facilitates expression of homeobox genes and is also required for sister chromatid cohesion. Nipped-B is conserved from yeast to man, and its orthologs also play roles in deoxyribonucleic acid repair and meiosis. Mutation of the human ortholog, Nipped-B-Like (NIPBL), causes Cornelia de Lange syndrome (CdLS), associated with multiple developmental defects. The Nipped-B protein family is required for the cohesin complex that mediates sister chromatid cohesion to bind to chromosomes. A key question, therefore, is whether the Nipped-B family regulates gene expression, meiosis, and development by controlling cohesin. To gain insights into Nipped-B's functions, we compared the effects of several Nipped-B mutations on gene expression, sister chromatid cohesion, and meiosis. We also examined association of Nipped-B and cohesin with somatic and meiotic chromosomes by immunostaining. Missense Nipped-B alleles affecting the same HEAT repeat motifs as CdLS-causing NIPBL mutations have intermediate effects on both gene expression and mitotic chromatid cohesion, linking these two functions and the role of NIPBL in human development. Nipped-B colocalizes extensively with cohesin on chromosomes in both somatic and meiotic cells and is present in soluble complexes
Genome-wide association studies have identified common variation in the CHRNA5-CHRNA3-CHRNB4 and CHRNA6-CHRNB3 gene clusters that contribute to nicotine dependence. However, the role of rare variation in risk for nicotine dependence in these nicotinic receptor genes has not been studied. We undertook pooled sequencing of the coding regions and flanking sequence of the CHRNA5, CHRNA3, CHRNB4, CHRNA6 and CHRNB3 genes in African American and European American nicotine-dependent smokers and smokers without symptoms of dependence. Carrier status of individuals harboring rare missense variants at conserved sites in each of these genes was then compared in cases and controls to test for an association with nicotine dependence. Missense variants at conserved residues in CHRNB4 are associated with lower risk for nicotine dependence in African Americans and European Americans (AA P = 0.0025, odds-ratio (OR) = 0.31, 95% confidence-interval (CI) = 0.31-0.72; EA P = 0.023, OR = 0.69, 95% CI = 0.50-0.95). Furthermore, these individuals were found to smoke fewer cigarettes per day than non-carriers (AA P = 6.6 × 10(-5), EA P = 0.021). Given the possibility of stochastic differences in rare allele frequencies between groups replication of this association is necessary to confirm these findings. The functional effects of the two CHRNB4 variants contributing most to this association (T375I and T91I) and a missense variant in CHRNA3 (R37H) in strong linkage disequilibrium with T91I were examined in vitro. The minor allele of each polymorphism increased cellular response to nicotine (T375I P = 0.01, T91I P = 0.02, R37H P = 0.003), but the largest effect on in vitro receptor activity was seen in the presence of both CHRNB4 T91I and CHRNA3 R37H (P = 2 × 10(-6)).
Adolescent idiopathic scoliosis (AIS) is a complex inherited spinal deformity whose etiology has been elusive. While common genetic variants are associated with AIS, they explain only a small portion of disease risk. To explore the role of rare variants in AIS susceptibility, exome sequence data of 391 severe AIS cases and 843 controls of European ancestry were analyzed using a pathway burden analysis in which variants are first collapsed at the gene level then by Gene Ontology terms. Novel non-synonymous/splice-site variants in extracellular matrix genes were significantly enriched in AIS cases compared with controls (P = 6 × 10(-9), OR = 1.7, CI = 1.4-2.0). Specifically, novel variants in musculoskeletal collagen genes were present in 32% (126/391) of AIS cases compared with 17% (146/843) of in-house controls and 18% (780/4300) of EVS controls (P = 1 × 10(-9), OR = 1.9, CI = 1.6-2.4). Targeted resequencing of six collagen genes replicated this association in combined 919 AIS cases (P = 3 × 10(-12), OR = 2.2, CI = 1.8-2.7) and revealed a highly significant single-gene association with COL11A2 (P = 6 × 10(-9), OR = 3.8, CI = 2.6-7.2). Importantly, AIS cases harbor mainly non-glycine missense mutations and lack the clinical features of monogenic musculoskeletal collagenopathies. Overall, our study reveals a complex genetic architecture of AIS in which a polygenic burden of rare variants across extracellular matrix genes contributes strongly to risk.
Genetic factors predictive of severe adolescent idiopathic scoliosis (AIS) are largely unknown. To identify genetic variation associated with severe AIS, we performed an exome-wide association study of 457 severe AIS cases and 987 controls. We find a missense SNP in SLC39A8 (p.Ala391Thr, rs13107325) associated with severe AIS (P = 1.60 × 10−7, OR = 2.01, CI = 1.54–2.62). This pleiotropic SNP was previously associated with BMI, blood pressure, cholesterol, and blood manganese level. We replicate the association in a second cohort (841 cases and 1095 controls) resulting in a combined P = 7.02 × 10−14, OR = 1.94, CI = 1.63–2.34. Clinically, the minor allele of rs13107325 is associated with greater spinal curvature, decreased height, increased BMI and lower plasma manganese in our AIS cohort. Functional studies demonstrate reduced manganese influx mediated by the SLC39A8 p.Ala391Thr variant and vertebral abnormalities, impaired growth, and decreased motor activity in slc39a8 mutant zebrafish. Our results suggest the possibility that scoliosis may be amenable to dietary intervention.
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