HDC and osteoporosis: They are precursors of osteoclasts [4] and also secrete osteoclastogenic factors such as IL-1 (interleukin-1), IL-6 and TNF-α (tumor necrosis factor-alpha) [5].Human studies have also shown relationships between the expression levels of certain genes in circulating monocytes and osteoporosis: annexin A2 (ANXA2) [6], signal transducer and activator of transcription 1 (STAT1) [7], chemokine (C-C motif) receptor 3 (CCR3), histidine decarboxylase (HDC), and glucocorticoid receptor (GCR) [8].