UNC13D and hemophagocytic syndrome: Primary-HLH (p-HLH) are a heterogeneous group, the most common form of which is caused by genetic defects in familial HLH (f-HLH) genes (perforin [PRF1] [5], Unch [UNC13D] [6, 7] and syntaxin [STX11 and STXBP2]) [8].