Our data showed a significant overexpression of the CHI3L1 gene, encoding for the circulating factor YKL-40, in a subgroup of AIS patients (biological endophenotype FG1), which drew our attention given that the AIS patients classified into this endophenotype are less prone to develop a severe scoliosis18 when compared to the other two groups (Supplementary Fig. 1). This evidence concerns the gene CHI3L1 and androgen insensitivity syndrome.