NOTCH4 and systemic lupus erythematosus: Within the Major Histocompatibility Complex (MHC) region, two relevant non-HLA genes have been identified: PSORS1C1 [15], whose specific function is still unknown, but which has been linked to other autoimmune diseases, including Systemic Lupus Erythematosus (SLE) [16], rheumatoid arthritis, and Behçet’s disease [17]; and NOTCH4 [18,19], which encodes a transmembrane receptor involved in the regulation of fibrosis and vascular function.