1. A method of classifying a human subject having adolescent idiopathic scoliosis (AIS) comprising: providing a cell sample isolated from the subject; detecting an impairment in melatonin-signaling pathway in the sample in the presence and in the absence of a known melatonin-signaling pathway agonist, wherein the impairment is detected by an accumulation of cyclic adenosine 5′-monophosphate (cAMP) in the cell sample as compared to that in a control cell sample whereby the results of the detecting step enables the classification of the subject having AIS in one AIS subgroup.