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Table 1 Classification of primary (genetic) and secondary (reactive) HLH [4648]

From: Macrophage Activation Syndrome: different mechanisms leading to a one clinical syndrome

Genetic HLH
Primary or Familial HLH (pHL)
 pHL-1 Unknown  
 pHL-2 PRF1 Pore-forming protein
 pHL-3 UNC13D Vesicle priming (impair granule exocytosis)
 pHL-4 STX11 Vesicle transport and fusion
 pHL-5 STXBP2 Vesicle transport and fusion
Sporadic associated with Immunodeficiencies
 CHS LYST Vesicle transport
 GS-2 RAB27A Vesicle docking
 XLP-1/XLP-2 SH2DIA/BIRC4 Signal transduction and activation of lymphocytes
Secondary HLH or Acquired HLH or Reactive HLH
 Infections (EBV, Leishmania, H1N1…)   
 Rheumatic diseases (sJIA…)→MAS or rheuma-HLH   
 Malignancies (lymphoma…)