POSTN and polycystic ovary syndrome: Bone marker proteins differed significantly between women with and without PCOS in the PCOS biobank cohort in whole-group analysis with changes in periostin, cathepsin L, osteocalcin and cathepsin D, but linear regression showed changes in cathepsins D and L and osteocalcin, with a trend for periostin and cathepsin Z. Tentatively this could suggest a shift to impaired bone formation and increased resorptive activity that would be in accord with reported studies suggesting that overall in PCOS, there is decreased BMD [9,13].