Adolescent idiopathic scoliosis (AIS) is the most common pediatric spinal deformity, affecting 2–3% of otherwise healthy children, with a 9:1 ratio of affected females: males for severe curvatures(1, 2). AIS is defined as a structural lateral spinal curvature of ≥ 10°, and typically manifests during the pre-adolescent period of rapid growth velocity(3–5). Radiographs of adolescents with a normal spine and with AIS, as measured by Cobb angle, are provided in Fig. 1. The high prevalence of AIS across populations, combined with potential morbidities related to functional deformity, social stigma, back pain, surgical interventions, and disease, have prompted costly school screening programs for early detection of scoliosis. The true clinical dilemma is to determine which children are at risk for AIS, and once diagnosed, which children are at risk for significant curve progression. Treatment options for scoliosis have remained stagnant for decades, and spinal fusion surgery is often advised for severe progressive curvatures with life-long implications. Together, the annual public health cost of pediatric screening, specialty referrals, bracing and surgery for AIS exceeds $3 billion USD annually, not accounting for adult morbidities, including chronic back pain, pulmonary and neurological complications, and secondary surgeries, thus contributing to the estimated $849 billion in annual costs for musculoskeletal conditions(6–9).
Decades of research into AIS families and population studies have established the strong heritability of AIS with significant sibling recurrence-risk ratio for both mild and severe curvatures(10, 11). While genetic heritability is high, studies of AIS families and large cohorts have consistently demonstrated significant heterogeneity indicative of the complex genetic nature of this disorder(12, 13). Whole exome sequencing (WES) and genome-wide association studies (GWAS) have resulted in a large number of potential predisposition genetic variants, such as those in or near LBX1, BNC2 and GPR126, which have been replicated across multiple populations. However, these variants correspond to only a modest increase in risk for AIS. Additionally, the biological roles of the most promising genetic variants in relation to AIS are unknown, thus, they have not led to a mechanistic understanding of the pathology related to this disorder.
The use of genetic variants in the clinical realm as therapeutic targets has achieved some clinical utility, particularly in relation to breast and colon cancer, and, more recently with the potential modulation of viruses, such as COVID-19 (14, 15). In relation to AIS, in 2010, a genetic screen of 53 single nucleotide polymorphisms (SNPs) for Caucasian children ages 9–13 years with mild scoliosis was designed to predict those most at-risk of severe curve progression (16). The genetic screen marketed as the ScoliScore (Transgenomics, Inc.) garnered mixed results upon validation, and it is unclear whether it offers any information for clinical decision making beyond a patient’s natural history (17–20). Nevertheless, genetic research related to AIS has continued to expand exponentially, with large population-based genome-wide association studies (GWAS)(21–27) and whole-exome sequencing (WES)(28–36) studies in both families and populations. These studies vary widely based on population, methodology, number of subjects and controls, statistical analyses, and interpretation of results (5, 37–40). A critical analysis of the existing information would be of great importance, not only to assist in research efforts related to AIS genetics, but also to aid in our ability to identify children for the onset of AIS, to prioritize those children at risk for AIS progression, and to develop targeted therapeutic interventions for a personalized medicine approach to this disorder (41). This manuscript is a systematic review to assist in this effort.
Our primary objective within this systematic review is to identify specific risk single-nucleotide polymorphisms (SNPs) for AIS through methodologies that provide significant variant level data (i.e. GWAS, next-generation DNA sequencing) on the diagnosis of AIS and, if diagnosed, the susceptibility of AIS curve progression.