In the first category, the main focus of research has included genes encoding the human leukocyte antigen (HLA) classes I and II and different molecules participating in the inflammatory response of GCA (IL-1β, IL-6, IL-10, IL-17A, IL-21, IL-23R, IL-33, TNF-α, VEGF, MMP-9, MPO, and others). This evidence concerns the gene MMP9 and temporal arteritis.