MPO is a common inflammatory marker, and elevated MPO levels are observed in many pathological conditions, including inflammatory bowel disease (IBD) [45,57,58,59], cardiovascular disease [60,61,62,63], obesity [43,64,65], liver disease [66,67], arthritis [68], multiple sclerosis [69,70], Alzheimer’s disease [71], stroke [72] and cancer [73,74] (Table 1). This evidence concerns the gene MPO and arthritic joint disease.