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The pathogenesis of adolescent idiopathic scoliosis (AIS), including the associated local changes in deep paravertebral muscles, is poorly understood. The asymmetric expression of several molecules involved in the melatonin signaling pathway, including melatonin receptors 1A/1B (MTNR1A/MTNR1B), estrogen receptor 2 (ESR2) and calmodulin (CALM1), has previously been suggested to be associated with AIS. However, this hypothesis is based on single studies in which the data were obtained by different methodological approaches. Therefore, to evaluate the symmetry of the mRNA expression levels of these molecules, 18 patients with AIS and 10 non‑scoliotic controls were enrolled in the present study. Muscle biopsy samples from deep paraspinal muscles (from the convexity and concavity of the scoliotic curve in patients with AIS, or from the left and right sides in controls) were obtained during spinal surgery. For each sample, the relative mRNA expression levels of MTNR1A, MTNR1B, CALM1 and ESR2 were analyzed by reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and were quantified according to the quantification cycle method. The results indicated that the mRNA expression levels of none of the investigated molecules were significantly different between samples obtained from the convex and concave side of the scoliotic curve in patients with AIS. In addition, no difference in expression was detected between the patients with AIS and the controls. With regards to MTNR1A and MTNR1B, their expression was very weak in paravertebral muscles, and in the majority of cases their expression could not be detected by repeated RT‑qPCR analysis. Therefore, these data do not support the previously suggested role of the asymmetric expression of molecules involved in the melatonin signaling pathway in deep paravertebral muscles in the pathogenesis of AIS.