Somewhat complicating matters are patients bearing pathogenic mutations in PSTPIP1 who were recently shown to have chronic elevation of total IL-18, detectable free IL-18: However their autoinflammatory clinical phenotype is characterized by pyogenic arthritis and neutrophilic dermatoses, but not by risk for or features suggestive of MAS, and can be easily differentiated clinically [28]. This evidence concerns the gene IL18 and bacterial arthritis.