PRF1 and hemophagocytic syndrome: Focus should also be on known genetic causes of hemophagocytic lymphohistiocytosis (HLH), including defects in the genes PRF1, UNC13D, STX11, STXBP2, LYST, RAB27A (164) either in the well-recognized homozygous forms, or possibly in heterozygous forms that may still predispose to HLH in the presence of a trigger, such as SARS-CoV-2 (165).