A previous study reported reduced BAIBA concentrations in the plasma of patients with major depressive disorder.61 HLys, which was found to have clinically relevant potential for baseline and post-surgery KOA, is characteristic of collagen and collagen-like proteins, produced by a post-translational modification of Lys, and crucial for collagen glycosylation and crosslinking.62 AABA has been previously suggested as a potential marker for depression in older adults, with reduced plasma levels in the depressive group,63 corroborating the findings of the current study. Here, COL20A1 is linked to depressive disorder.