Genome-wide methylation association study in monozygotic twins discordant for curve severity of adolescent idiopathic scoliosis.

Background context: Emerging evidence suggests that abnormal DNA methylation patterns may play a role in the progression of adolescent idiopathic scoliosis (AIS). However, the mechanisms underlying the influence of DNA methylation on curve severity remain largely unknown.

Purpose: To characterize the DNA methylation profiles associated with the curve severity of AIS.

Study design: Retrospective study with prospectively collected clinical data and blood samples.

Methods: A total of 7 AIS monozygotic twin pairs discordant for curve severity were included. Genome-wide methylation profile from blood samples were quantified by Illumina Infinium MethylationEPIC BeadChip (850K chip). Cell type composition of the samples was estimated by RefbaseEWAS method. Differentially methylated CpG sites were identified through comparison between patients with low and high Cobb angle. We also performed a gene-based collapsing analysis using mCSEA by aggregating the CpG sites based on promoter region. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis were performed using clusterProfiler package.

Results: Genome-wide DNA methylation analysis identified multiple differentially methylated positions across the genome. Gene-based collapsing analysis identified 212 differentially methylated genes (FDR adjusted p<0.05), most of which (186/212) were hypermethylated in the group with high Cobb angle. Some of the identified genes were well-documented in AIS literature, such as TBX1, PAX3 and LBX1. Functional enrichment analysis revealed that the differentially methylated genes (DMGs) were involved in pattern specification process, skeletal development, muscle function, neurotransmission and several signaling pathways (cAMP, Wnt and prolactin).

Conclusions: The study represents the largest systematic epigenomic analyses of monozygotic twins discordant for curve severity and supports the important role of altered DNA methylation in AIS.

Clinical significance: The identified CpG sites provide insight into novel biomarkers predicting curve progression of AIS. Furthermore, the differentially methylated genes and enriched pathways may serve as interventional therapy target for AIS patients.