ISG15 and systemic lupus erythematosus: The IFN6 score (calculated with SIGLEC1, IFI27, IFI44L, IFIT1, ISG15, and RSAD2 relative expression) using RT-qPCR in SLE patients had 89% sensitivity and 72% specificity using pediatric patients in the interferonopathy group (SLE, dermatomyositis, and connective tissue disease) and non-interferonopathy (juvenile idiopathic arthritis and healthy controls) [13].