In hematology, hemophagocytic lymphohistiocytosis (HLH), also known as haemophagocytic lymphohistiocytosis (British spelling), and hemophagocytic or haemophagocytic syndrome, is an uncommon hematologic disorder seen more often in children than in adults. It is a life-threatening disease of severe hyperinflammation caused by uncontrolled proliferation of benign lymphocytes and macrophages that secrete high amounts of inflammatory cytokines. It is classified as one of the cytokine storm syndromes. There are inherited and non-inherited (acquired) causes of HLH.

Reference
Wiki: Familial hemophagocytic lymphohistiocytosis