Table 3.

Epigenetic factors associated with AIS progression (NS = non-specified, OR = odds ratio, AUC = area under the curve).

Epigenetic Marker	Technique	Biological Sample	Molecular Pathway	Sensitivity/Specificity	p-Value	Results	Reference
cg01374129 demethylation status correlates with disease progression (HAS2 as candidate gene).	Whole-exome sequencing and quantitative DNA methylation analysis by Massarray	Peripheral blood cell DNA of AIS discordant monozygotic twin pairs	The Wnt/β-catenin signaling pathway plays a prominent role in maintaining cellular homeostasis, bone formation, and remodeling.	Sensitivity: 76.4%, Specificity: 85.6% AUC = 0.827 within 95% Confidence interval (CI): 0.780–0.876	<0.0001	Methylation level of cg01374129 site (Has2 gene) was significantly lower in the progression group than in the non-progression group. Cg01374129 methylation as biomarker achieved a sensitivity of 76.4% and a specificity of 85.6% in differentiating patients with and without curve progression.	Y. Meng (2018)
cg02477677, cg12922161, cg08826461, and cg16382077 methylation associated with curve severity (WNT10A and NPY as candidate genes)	Array-based genome-wide methylation analysis	Peripheral blood cell DNA of AIS monozygotic twin pairs	WNT signaling pathway relevant for bone formation and remodeling; neuropeptide Y (NPY), regulator of bone and energy homeostasis	NS	=0.494, FDR adjusted p-value = 0.41329	Hypomethylation of four CpG sites was associated with curve severity (cg02477677, cg12922161, cg08826461, and cg1638077). Annotation of two of the regions implicated the NPY gene on chr. 7 and the WNT10A gene on chr. 2	P. Carry (2021)
Overexpression of miR145 of Wnt/β-catenin signaling pathway	Array-based miRNA expression analysis	Iliac crest bone tissue cells of AIS patients and serum	WNT signaling pathway relevant to bone formation and remodeling	Sensitivity 72.7% Specificity 90% AUC = 0.93; within 95% Confidence Interval (CI): 0.88–0.98	<0.05	Significant negative correlations between circulating miR-145 and serum sclerostin, osteopontin, and osteoprotegerin in AIS patients and not in control group. Aberrant miRNA expression may contribute to low bone mass and affect osteocyte function, with possible involvement in AIS pathogenesis.	J. Zhang (2018)
COMP promoter methylation associated with curve severity	Pyrosequencing	Peripheral blood cell DNA of AIS patients and controls	COMP (cartilage oligomerix matrix protein) belongs to the trombospondin gene family and is a marker of cartilage turnover.	NS	<0.001	The methylation level of five CpGs in the COMP promoter was significantly correlated with Cobb angle of the main curve and chronological age (p < 0.0001).	S. Mao (2018)
PITX1 promoter methylation associated with Cobb angle	Pyrosequencing	Peripheral blood cell DNA of AIS patients and controls	PITX1 is a member of the RIEG/PITX homeobox transcription factor family, involved in organ development. Mutations in this gene have been associated with various bone-related diseases.	NS	<0.001	The methylation level of 6 CpG sites in PITX1 promoter was significantly associated with Cobb angle of the main curve. The comparative analysis showed significant difference in age (p = 0.021) and Cobb angle of the main curve (p = 0.0001) between AIS groups with positive and negative methylation.	B. Shi (2018)
PCDH10 promoter methylation level associated with Cobb angle	Pyrosequencing	Peripheral blood cell DNA of controls and AIS patients	protocadherin10 (PCDH10) gene, involved in immune process and Wnt	NS	<0.001	AIS patients were associated with high Higher DNA methylation level and low gene expression of PCDH10 gene rather than normal controls. The high methylation level indicated high Cobb angle of major curves in AIS. The abnormal DNA methylation may widely exist and serve as a potential mechanism for AIS progression. The average methylation level was 4.32 ± 0.73 in AIS patients and 3.14 ± 0.97 in healthy controls (p < 0.001). Besides, the PCDH10 gene expression was 0.23 ± 0.04 in AIS patients and 0.36 ± 0.08 in normal controls (p < 0.001).	B. Shi (2019)
H19 downregulation and ADIPOQ upregulation in concave-sided muscle correlate positively with curve severity and age at initiation.	RNA-seq	Paravertebral muscle concave and convex muscles of AIS patients	ADIPOQ (PARR signaling pathway, gene encoding for adiponectin) and H19 (long non-coding RNA generating miR-675-5p and miR-675-3p) H19 can promote skeletal muscle differentiation and regeneration and regulate glucose metabolism.	NS	<0.001 0.011 <0.001 0.039	RNA-seq revealed transcriptomic differences between two sides of paravertebral muscle in AIS patients. This implies that transcriptomic differences caused by epigenetic factors in affected individuals may account for the structural and functional imbalance of paravertebral muscle, which can expand the understanding of this disease progression. Comparing features of clinical characteristics, such as the magnitude of spinal curve, age at menarche, body mass index and age at initiation, between different samples with different ADIPOQ and H19 expression patterns. The relative expression difference of H19 (concave–convex) was significantly correlated with Cobb’s angle (r = 0.638, p < 0.001) and age at initiation (r = − 0.295, p = 0.011), and the relative expression difference of ADPOQ mRNA (concave-convex) was also significantly correlated with spinal curve (r = − 0.4926, p < 0.001) and age at initiation (r = 0.230, p = 0.039). These data suggest an important role of H19 and ADIPOQ in the onset or progression of scoliosis.	H. Jiang (2018)
T-DMR1 and T-DMR2 regions of ESR1 gene methylation associated with AIS severity	Pyrosequencing	Paraspinal superficial and deep muscles of AIS patients	Estrogen receptor	NS	0.02 0.04 0.04 0.05	In the deep paravertebral muscle, the methylation level within the ESR1 T-DMR2 region on the concave side of the curvature was significantly different between groups of patients with a Cobb angle >70° or <70° at four CpG sites: CPG2, CPG3, CPG4, and CPG6. No differences were observed in T-DMR1 methylation levels between groups of patients with Cobb angles <70° and >70°.	P. Janusz, (2021)
miR-151a-3p (targeting GREM1)	NGS Small RNA sequencing	Cell-free RNA from peripheral blood plasma of severe and mild AIS patients and controls	Skeletal homeostasis	AUC = 0.885 within 95% Confidence Interval (CI): 0.815–0.936	<0.05	miR-151a-3p and GREM1 expression significantly correlated with severe AIS curves. Plasma miR-151a-3p might serve as a biomarker for severe AIS. The overexpression of miR-151a-3p may contribute to the progression of scoliosis via inhibition of GREM1 expression in osteoblasts to interrupt bone homeostasis. Finally, relatively lower methylation levels of the promoter of miR-151a-3p might explain high miR-151a-3p levels. This may provide a new biomarker for the early detection of AIS and increase our understanding of the progression of AIS.	Wang (2020)