HDC and osteoporosis: In addition, human studies have found associations of gene expression levels in circulating monocytes and osteoporosis, such as ANXA2 (annexin A2) [26], STAT1 (signal transducer and activator of transcription 1) [27], CCR3 [chemokine (C-C motif) receptor 3], HDC (histidine decarboxylase), and GCR (glucocorticoid receptor) [28].