MMP9 and complex regional pain syndrome: The expression levels of 6 of those 10 genes (HLA-A29.1, MMP9, ANPEP, HDC, G-CSF3R, and STAT3) were significantly different between CRPS patients and controls (p = 0.004, 1.4×10−4, 0.017, 0.004, 0.017, and 0.017, respectively).