Comprehensive In Vivo Interrogation Reveals Phenotypic Impact of Human Enhancer Variants.

Establishing causal links between non-coding variants and human phenotypes is an increasing challenge. Here, we introduce a high-throughput mouse reporter assay for assessing the pathogenic potential of human enhancer variants in vivo and examine nearly a thousand variants in an enhancer repeatedly linked to polydactyly. We show that 71% of all rare non-coding variants previously proposed as causal lead to reporter gene expression in a pattern consistent with their pathogenic role. Variants observed to alter enhancer activity were further confirmed to cause polydactyly in knockin mice. We also used combinatorial and single-nucleotide mutagenesis to evaluate the in vivo impact of mutations affecting all positions of the enhancer and identified additional functional substitutions, including potentially pathogenic variants hitherto not observed in humans. Our results uncover the functional consequences of hundreds of mutations in a phenotype-associated enhancer and establish a widely applicable strategy for systematic in vivo evaluation of human enhancer variants.

Exome sequencing of 1190 non-syndromic clubfoot cases reveals HOXD12 as a novel disease gene.

BACKGROUND: Clubfoot, presenting as a rigid inward and downward turning of the foot, is one of the most common congenital musculoskeletal anomalies. The aetiology of clubfoot is poorly understood and variants in known clubfoot disease genes account for only a small portion of the heritability. METHODS: Exome sequence data were generated from 1190 non-syndromic clubfoot cases and their family members from multiple ethnicities. Ultra-rare variant burden analysis was performed comparing 857 unrelated clubfoot cases with European ancestry with two independent ethnicity-matched control groups (1043 in-house and 56 885 gnomAD controls). Additional variants in prioritised genes were identified in a larger cohort, including probands with non-European ancestry. Segregation analysis was performed in multiplex families when available. RESULTS: Rare variants in 29 genes were enriched in clubfoot cases, including PITX1 (a known clubfoot disease gene), HOXD12, COL12A1, COL9A3 and LMX1B. In addition, rare variants in posterior HOX genes (HOX9-13) were enriched overall in clubfoot cases. In total, variants in these genes were present in 8.4% (100/1190) of clubfoot cases with both European and non-European ancestry. Among these, 3 are de novo and 22 show variable penetrance, including 4 HOXD12 variants that segregate with clubfoot. CONCLUSION: We report HOXD12 as a novel clubfoot disease gene and demonstrate a phenotypic expansion of known disease genes (myopathy gene COL12A1, Ehlers-Danlos syndrome gene COL9A3 and nail-patella syndrome gene LMX1B) to include isolated clubfoot.

Rare and de novo coding variants in chromodomain genes in Chiari I malformation.

Chiari I malformation (CM1), the displacement of the cerebellum through the foramen magnum into the spinal canal, is one of the most common pediatric neurological conditions. Individuals with CM1 can present with neurological symptoms, including severe headaches and sensory or motor deficits, often as a consequence of brainstem compression or syringomyelia (SM). We conducted whole-exome sequencing (WES) on 668 CM1 probands and 232 family members and performed gene-burden and de novo enrichment analyses. A significant enrichment of rare and de novo non-synonymous variants in chromodomain (CHD) genes was observed among individuals with CM1 (combined p = 2.4 × 10-10), including 3 de novo loss-of-function variants in CHD8 (LOF enrichment p = 1.9 × 10-10) and a significant burden of rare transmitted variants in CHD3 (p = 1.8 × 10-6). Overall, individuals with CM1 were found to have significantly increased head circumference (p = 2.6 × 10-9), with many harboring CHD rare variants having macrocephaly. Finally, haploinsufficiency for chd8 in zebrafish led to macrocephaly and posterior hindbrain displacement reminiscent of CM1. These results implicate chromodomain genes and excessive brain growth in CM1 pathogenesis.

Genetic association and characterization of FSTL5 in isolated clubfoot.

Talipes equinovarus (clubfoot, TEV) is a congenital rotational foot deformity occurring in 1 per 1000 births with increased prevalence in males compared with females. The genetic etiology of isolated clubfoot (iTEV) remains unclear. Using a genome-wide association study, we identified a locus within FSTL5, encoding follistatin-like 5, significantly associated with iTEV. FSTL5 is an uncharacterized gene whose potential role in embryonic and postnatal development was previously unstudied. Utilizing multiple model systems, we found that Fstl5 was expressed during later stages of embryonic hindlimb development, and, in mice, expression was restricted to the condensing cartilage anlage destined to form the limb skeleton. In the postnatal growth plate, Fstl5 was specifically expressed in prehypertrophic chondrocytes. As Fstl5 knockout rats displayed no gross malformations, we engineered a conditional transgenic mouse line (Fstl5LSL) to overexpress Fstl5 in skeletal osteochondroprogenitors. We observed that hindlimbs were slightly shorter and that bone mineral density was reduced in adult male, but not female, Prrx1-cre;Fstl5LSL mice compared with control. No overt clubfoot-like deformity was observed in Prrx1-cre;Fstl5LSL mice, suggesting FSTL5 may function in other cell types to contribute to iTEV pathogenesis. Interrogating published mouse embryonic single-cell expression data showed that Fstl5 was expressed in cell lineage subclusters whose transcriptomes were associated with neural system development. Moreover, our results suggest that lineage-specific expression of the Fstl genes correlates with their divergent roles as modulators of transforming growth factor beta and bone morphogenetic protein signaling. Results from this study associate FSTL5 with iTEV and suggest a potential sexually dimorphic role for Fstl5 in vivo.

Whole Exome Sequencing in Individuals with Idiopathic Clubfoot Reveals a Recurrent Filamin B (FLNB) Deletion.

BACKGROUND: Clubfoot, a congenital deformity that presents as a rigid, inward turning of the foot, affects approximately 1 in 1000 infants and occurs as an isolated birth defect in 80% of patients. Despite its high level of heritability, few causative genes have been identified, and mutations in known genes are only responsible for a small portion of clubfoot heritability. QUESTIONS/PURPOSES: (1) Are any rare gene variants enriched (that is, shared) in unrelated patients with isolated clubfoot? (2) Are there other rare variants in the identified gene (Filamin B) in these patients with clubfoot? METHODS: Whole-exome sequence data were generated from a discovery cohort of 183 unrelated probands with clubfoot and 2492 controls. Variants were filtered with minor allele frequency < 0.02 to identify rare variants as well as small insertions and deletions (indels) resulting in missense variants, nonsense or premature truncation, or in-frame deletions. A candidate deletion was then genotyped in another cohort of 974 unrelated patients with clubfoot (a replication cohort). Other rare variants in the candidate gene were also investigated. A segregation analysis was performed in multigenerational families of individuals with clubfoot to see if the genotypes segregate with phenotypes. Single-variant association analysis was performed using the Fisher two-tailed exact test (exact p values are presented to give an indication of the magnitude of the association). RESULTS: There were no recurrent variants in the known genes causing clubfoot in this study. A three-base pair in-frame codon deletion of Filamin B (FLNB) (p.E1792del, rs1470699812) was identified in 1.6% (3 of 183) of probands with clubfoot in the discovery cohort compared with 0% of controls (0 of 2492) (odds ratio infinity (inf) [95% CI 5.64 to inf]; p = 3.18 x 10-5) and 0.0016% of gnomAD controls (2 of 125,709) (OR 1.01 x 103 [95% CI 117.42 to 1.64 x 104]; p = 3.13 x 10-8). By screening a replication cohort (n = 974 patients), we found two probands with the identical FLNB deletion. In total, the deletion was identified in 0.43% (5 of 1157) of probands with clubfoot compared with 0% of controls and 0.0016% of gnomAD controls (OR 268.5 [95% CI 43.68 to 2.88 x 103]; p = 1.43 x 10-9). The recurrent FLNB p.E1792del variant segregated with clubfoot, with incomplete penetrance in two families. Affected individuals were more likely to be male and have bilateral clubfoot. Although most patients had isolated clubfoot, features consistent with Larsen syndrome, including upper extremity abnormalities such as elbow and thumb hypermobility and wide, flat thumbs, were noted in affected members of one family. We identified 19 additional rare FLNB missense variants located throughout the gene in patients with clubfoot. One of these missense variants, FLNB p.G2397D, exhibited incomplete penetrance in one family. CONCLUSION: A recurrent FLNB E1792 deletion was identified in 0.43% of 1157 isolated patients with clubfoot. Given the absence of any recurrent variants in our discovery phase (n = 183) for any of the known genes causing clubfoot, our findings support that novel and rare missense variants in FLNB in patients with clubfoot, although rare, may be among the most commonly known genetic causes of clubfoot. Patients with FLNB variants often have isolated clubfoot, but they and their family members may be at an increased risk of having additional clinical features consistent with Larsen syndrome. CLINICAL RELEVANCE: Identification of FLNB variants may be useful for determining clubfoot recurrence risk and comorbidities.

Rare and de novo duplications containing SHOX in clubfoot.

INTRODUCTION: Congenital clubfoot is a common birth defect that affects at least 0.1% of all births. Nearly 25% cases are familial and the remaining are sporadic in inheritance. Copy number variants (CNVs) involving transcriptional regulators of limb development, including PITX1 and TBX4, have previously been shown to cause familial clubfoot, but much of the heritability remains unexplained. METHODS: Exome sequence data from 816 unrelated clubfoot cases and 2645 in-house controls were analysed using coverage data to identify rare CNVs. The precise size and location of duplications were then determined using high-density Affymetrix Cytoscan chromosomal microarray (CMA). Segregation in families and de novo status were determined using qantitative PCR. RESULTS: Chromosome Xp22.33 duplications involving SHOX were identified in 1.1% of cases (9/816) compared with 0.07% of in-house controls (2/2645) (p=7.98×10-5, OR=14.57) and 0.27% (38/13592) of Atherosclerosis Risk in Communities/the Wellcome Trust Case Control Consortium 2 controls (p=0.001, OR=3.97). CMA validation confirmed an overlapping 180.28 kb duplicated region that included SHOX exons as well as downstream non-coding regions. In four of six sporadic cases where DNA was available for unaffected parents, the duplication was de novo. The probability of four de novo mutations in SHOX by chance in a cohort of 450 sporadic clubfoot cases is 5.4×10-10. CONCLUSIONS: Microduplications of the pseudoautosomal chromosome Xp22.33 region (PAR1) containing SHOX and downstream enhancer elements occur in ~1% of patients with clubfoot. SHOX and regulatory regions have previously been implicated in skeletal dysplasia as well as idiopathic short stature, but have not yet been reported in clubfoot. SHOX duplications likely contribute to clubfoot pathogenesis by altering early limb development.

Distal chromosome 16p11.2 duplications containing SH2B1 in patients with scoliosis.

INTRODUCTION: Adolescent idiopathic scoliosis (AIS) is a common musculoskeletal disorder with strong evidence for a genetic contribution. CNVs play an important role in congenital scoliosis, but their role in idiopathic scoliosis has been largely unexplored. METHODS: Exome sequence data from 1197 AIS cases and 1664 in-house controls was analysed using coverage data to identify rare CNVs. CNV calls were filtered to include only highly confident CNVs with >10 average reads per region and mean log-ratio of coverage consistent with single-copy duplication or deletion. The frequency of 55 common recurrent CNVs was determined and correlated with clinical characteristics. RESULTS: Distal chromosome 16p11.2 microduplications containing the gene SH2B1 were found in 0.7% of AIS cases (8/1197). We replicated this finding in two additional AIS cohorts (8/1097 and 2/433), resulting in 0.7% (18/2727) of all AIS cases harbouring a chromosome 16p11.2 microduplication, compared with 0.06% of local controls (1/1664) and 0.04% of published controls (8/19584) (p=2.28×10-11, OR=16.15). Furthermore, examination of electronic health records of 92 455 patients from the Geisinger health system showed scoliosis in 30% (20/66) patients with chromosome 16p11.2 microduplications containing SH2B1 compared with 7.6% (10/132) of controls (p=5.6×10-4, OR=3.9). CONCLUSIONS: Recurrent distal chromosome 16p11.2 duplications explain nearly 1% of AIS. Distal chromosome 16p11.2 duplications may contribute to scoliosis pathogenesis by directly impairing growth or by altering expression of nearby genes, such as TBX6. Individuals with distal chromosome 16p11.2 microduplications should be screened for scoliosis to facilitate early treatment.

Massively parallel single-nucleotide mutagenesis using reversibly terminated inosine.

Large-scale mutagenesis of target DNA sequences allows researchers to comprehensively assess the effects of single-nucleotide changes. Here we demonstrate the construction of a systematic allelic series (SAS) using massively parallel single-nucleotide mutagenesis with reversibly terminated deoxyinosine triphosphates (rtITP). We created a mutational library containing every possible single-nucleotide mutation surrounding the active site of the TEM-1 ß-lactamase gene. When combined with high-throughput functional assays, SAS mutational libraries can expedite the functional assessment of genetic variation.

Use of Combined Botulinum Toxin and Physical Therapy for Treatment Resistant Congenital Muscular Torticollis.

BACKGROUND: Physical therapy (PT) alone is not always effective for treatment of congenital muscular torticollis (CMT). The adjunctive use of botulinum toxin (BTX) injection into the sternocleidomastoid, followed by PT, could provide correction and avoid more invasive surgery. Aims of the study were to review clinical and caregiver-reported outcomes of children with resistant CMT treated by BTX injection combined with a guided-PT program. METHODS: Medical records of consecutive children with resistant CMT treated by our protocol between 2010 and 2015 were reviewed. A minimum 2-year follow-up was required. Demographic parameters, numbers of BTX required and pre-BTX and post-BTX head tilt and range of neck rotation were recorded. A univariate analysis test was conducted to identify variables related to the need of repeated BTX injections. A phone interview with the caregivers was done regarding their satisfaction. RESULTS: A cohort of 39 patients with treatment resistant CMT were identified that had an average age of 14 (range, 6.5 to 27.6) months at initiation of BTX treatment. Multiple BTX injections were utilized in 21/39 (54%) of patients. No patient required tendon lengthening surgery. At the final evaluation, there was improvement in both head tilt (18.7±6.8 degrees vs. 1.7±2.4 degrees, mean difference (95% CI) 16.9 (14.6-19.3); P<0.001) and range of neck motion (56.0°±11.7 degrees vs. 86.0±3.8 degrees, mean difference (95% CI) 30.0 (26.1-33.9), P<0.001). Pre-BTX parameters were not associated with the requirement of repeated BTX injections (P>0.05). Caregivers were satisfied with the treatment protocol. No untoward effect was observed during the study period. CONCLUSIONS: The proposed minimally invasive protocol provided correction of resistant CMT and obviated the need for more invasive surgical procedures. LEVEL OF EVIDENCE: Level IV.

A polygenic burden of rare variants across extracellular matrix genes among individuals with adolescent idiopathic scoliosis.

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.

What Factors Influence Union and Refracture of Congenital Pseudarthrosis of the Tibia? A Multicenter Long-term Study.

OBJECTIVE: To identify factors influencing union of congenital pseudarthrosis of the tibia (CPT), refractures, and integrity of the tibia at maturity. METHODS: Data of 119 children operated for Crawford-type IV CPT and followed-up till skeletal maturity were analyzed. Logistic regression and recursive partitioning analyses were used to test associations between several variables and the outcome. RESULTS: Primary union occurred in 86% of children. At maturity, 69% remained soundly united. The odds ratio for failure of primary union was 3.89 (95% confidence interval, 1.05-14.40; P=0.042) when bone morphogenetic protein was used, and children who had a combination of the Ilizarov technique and intramedullary nailing were at risk for unsound union at maturity (odds ratio, 6.19; 95% confidence interval, 1.24-30.83; P=0.026). No other association reached statistical significance. On recursive partitioning, use of the Ilizarov technique, transfixing the ankle and subtalar joints, use of cortical graft and not operating on the fibula were associated with a better outcome; use of bone morphogenetic protein and combining intramedullary nailing with the Ilizarov technique were associated with poor results. CONCLUSIONS: A larger sample is needed to confirm which factors truly influence the outcome of CPT. This may be feasible if data are collected prospectively through a multicenter registry.

Deletions of 5' HOXC genes are associated with lower extremity malformations, including clubfoot and vertical talus.

BACKGROUND: Deletions of the HOXC gene cluster result in variable phenotypes in mice, but have been rarely described in humans. OBJECTIVE: To report chromosome 12q13.13 microdeletions ranging from 13 to 175 kb and involving the 5' HOXC genes in four families, segregating congenital lower limb malformations, including clubfoot, vertical talus and hip dysplasia. METHODS: Probands (N=253) with clubfoot or vertical talus were screened for point mutations and copy number variants using multiplexed direct genomic selection, a pooled BAC targeted capture approach. SNP genotyping included 1178 probands with clubfoot or vertical talus and 1775 controls. RESULTS: The microdeletions share a minimal non-coding region overlap upstream of HOXC13, with variable phenotypes depending upon HOXC13, HOXC12 or the HOTAIR lncRNA inclusion. SNP analysis revealed HOXC11 p.Ser191Phe segregating with clubfoot in a small family and enrichment of HOXC12 p.Asn176Lys in patients with clubfoot or vertical talus (rs189468720, p=0.0057, OR=3.8). Defects in limb morphogenesis include shortened and overlapping toes, as well as peroneus muscle hypoplasia. Finally, HOXC and HOXD gene expression is reduced in fibroblasts from a patient with a 5' HOXC deletion, consistent with previous studies demonstrating that dosage of lncRNAs alters expression of HOXD genes in trans. CONCLUSIONS: Because HOXD10 has been implicated in the aetiology of congenital vertical talus, variation in its expression may contribute to the lower limb phenotypes occurring with 5' HOXC microdeletions. Identification of 5' HOXC microdeletions highlights the importance of transcriptional regulators in the aetiology of severe lower limb malformations and will improve their diagnosis and management.

The 2017 ABJS Nicolas Andry Award: Advancing Personalized Medicine for Clubfoot Through Translational Research.

BACKGROUND: Clubfoot is one of the most common pediatric orthopaedic disorders. While the Ponseti method has revolutionized clubfoot treatment, it is not effective for all patients. When the Ponseti method does not correct the foot, patients are at risk for lifelong disability and may require more-extensive surgery. QUESTIONS/PURPOSES: (1) What genetic and morphologic abnormalities contribute to the development of clubfoot? (2) How can this information be used to devise personalized treatment paradigms for patients with clubfoot? METHODS: Human gene sequencing, molecular genetic engineering of mouse models of clubfoot, MRI of clubfoot, and development of new treatment methods all have been used by our group to understand the biological basis and improve therapy for this group of disorders. RESULTS: We gained new insight into clubfoot pathogenesis from our discovery that mutations in the PITX1-TBX4-HOXC transcriptional pathway cause familial clubfoot and vertical talus in a small number of families, with the unique lower limb expression of these genes providing an explanation for the lack of upper extremity involvement in these disorders. MRI studies revealed corresponding morphologic abnormalities, including hypomorphic muscle, bone, and vasculature, that are not only associated with these gene mutations, but also are biomarkers for treatment-resistant clubfoot. CONCLUSIONS: Based on an understanding of the underlying biology, we improved treatment methods for neglected and syndromic clubfoot, developed new treatment for congenital vertical talus based on the principles of the Ponseti method, and designed a new dynamic clubfoot brace to improve strength and compliance.

Erratum to: Editorial: Do Orthopaedic Surgeons Belong on the Sidelines at American Football Games?

In the November Editorial, "Editorial: Do Orthopaedic Surgeons Belong on the Sidelines at American Football Games?" a statistic was attributed to a JAMA study (Ref. 10) that should have been attributed to an article from the New York Times (Ref. 16). The sentence in question should read: "We accept that critique, provided that the skeptics acknowledge that the best-case estimate in support of the safety of football would result in a CTE prevalence estimate of 9%, since only another 1200 ex-NFL players have died [16] since this research group [10] began studying football players' brains."

Fat Graft and Bone Wax Interposition Provides Better Functional Outcomes and Lower Reossification Rates Than Extensor Digitorum Brevis After Calcaneonavicular Coalition Resection.

BACKGROUND: Calcaneonavicular coalitions are the most common form of tarsal coalitions. The prefered treatment for symptomatic coalitions is surgical resection; however, there are no published studies that directly compare different interposition techniques. The purpose of the present study was to retrospectively compare pain relief, functional outcomes, and complications of children and adolescents who had a resection of a symptomatic calcaneonavicular coalition with interposition of fat graft, bone wax, or extensor digitorum brevis (EDB). METHODS: In total, 48 patients (56 ft) underwent calcaneonavicular coalition resection-interposition at 3 institutions from July 2008 to July 2015. There were 23 feet in group 1 (fat graft), 18 feet in group 2 (bone wax), and 15 feet in group 3 (EDB). Patient demographic characteristics were similar between all groups for age, sex, coalition type, and symptoms onset. Data concerning clinical and radiographic features, surgical technique, and postoperative complications were obtained from all available medical records. Radiographs were evaluated at last follow-up to determine coalition regrowth. Preoperative and postoperative pain was assessed with the visual analog scale, and function was assessed with use of the American-Orthopaedic-Foot and Ankle Society (AOFAS) score. RESULTS: Pain improved to an average of 0.5 in the first group (range, 0 to 6), 0 in group 2, and 1.7 in group 3 (range, 0 to 5) (P=0.033). The average AOFAS score improved from 59 (range, 33 to 71 points) to 98 points (range, 62 to 100 points) in the fat graft group, from 50 (range, 34 to 62 points) to 98 points (range, 88 to 100 points) in the bone wax group, and from 48 (range, 30 to 60 points) to 75 points (range, 70 to 95 points) in the EDB group (P<0.001). Eight feet had regrowth of the coalition on the postoperative radiographs: 1 in group 1 (4%), 1 in group 2 (6%), and 6 in group 3 (40%) (P=0.004). Five feet from the third group developed progressive symptoms. CONCLUSIONS: In our study, autogenous fat graft and bone wax interposition techniques provided better pain relief, gave better functional scores, and avoided more effectively coalition reossification than EDB technique. Further studies are required to evaluate safety of bone wax as an interposition material. LEVEL OF EVIDENCE: Level III-therapeutic.

Surgical Reconstruction for Talocalcaneal Coalitions With Severe Hindfoot Valgus Deformity.

INTRODUCTION: Coalition resection can restore motion, and improve pain in patients with talocalcaneal coalitions (TCCs) and an aligned foot. However, there is some debate regarding appropriate treatment of patients with associated valgus deformity. The purpose of this study was to present the outcomes and complications following surgical reconstruction, with or without coalition resection, in a series of patients with TCC and severe hindfoot valgus. METHODS: Thirteen consecutive patients (14 feet) were evaluated. Eleven patients were male. Mean age was 14 years. Mean follow-up was 43.8 months. Seven patients (8 feet) underwent simultaneous resection of the coalition and reconstruction, and 6 patients (6 feet) isolated reconstruction. The talar-first metatarsal angle, the talar-horizontal angle, and calcaneal pitch were measured preoperatively and postoperatively. Clinical evaluation was made according to the American Orthopaedic Foot and Ankle Society ankle-hindfoot score. RESULTS: All radiographic values improved significantly and were within the normal ranges postoperatively. The average American Orthopaedic Foot and Ankle Society ankle-hindfoot score had improved from 45 to 98 points (P<0.001) in the group of simultaneous resection and reconstruction, and from 60 to 92.3 points (P=0.002) in the group of isolated reconstruction. All patients were asymptomatic at the last follow-up and were satisfied with the procedure. DISCUSSION: Surgical reconstruction with or without coalition resection can achieve significant functional and radiographic improvements, and symptoms relief in selected patients with TCCs and severe valgus deformity. LEVEL OF EVIDENCE: Level IV-therapeutic study.

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.