ESR1 and scoliosis: As this region is associated with AIS only in females,10 and as female Xe1+PEC7 KO mice show higher kinky tail penetrance, we hypothesized that estrogen could be involved in this process, based on previous reports associating it with AIS.32 Previous work showed that tamoxifen, a selective ESR modulator, decreases the rate of curve progression in a melatonin-deficient bipedal scoliosis mouse model.33 We thus injected tamoxifen into Xe1+PEC7 KO E17.5 pregnant females and compared their kinky tail phenotypic ratio of pups at day 21 to un-injected mice.