CTSZ and osteoporosis: Overall, the levels of cathepsin Z mRNA in isolated PBMCs were significantly inversely-associated with bone mineral density (Fig. 3): mean lumbar spine L2-L4 T-score (Fig. 3a) (y = −0.071645×+0.219589, r2 = 0.152, P = 0.0002, linear regression), significantly inversely with femoral neck T-score (Fig. 3b) (y = −0.065515×+0.213781, r2 = 0.0698, P = 0.0139) and significantly inversely associated with bone mineral density (BMD) (g/cm2) (Fig. 3c) (y = −0.553049×+0.760755; r2 = 0.07, P = 0.0149), strengthening the observed relationship between cathepsin Z mRNA levels and osteoporosis.