PRF1 and Familial hemophagocytic lymphohistiocytosis: Gene defects in FHL2-Perforin (PRF1), FHL3-Munc13-4 (UNC13D), and FHL4-Syntaxin11 (STX11) have been linked to familial HLH [15-17]. Protein defects involving the MUNC13-4 protein and RAB27A protein have been detected [15-17].