CD27 and hemophagocytic syndrome: EBV-triggered HLH usually occurs in patients with X-linked lymphoproliferative disorder type 1 (XLP1), X-linked lymphoproliferative disorder type 2 (XLP2), IL-2-inducible T cell kinase deficiency, CD27 deficiency, and X-linked immunodeficiency with magnesium defect (XMEM) [1].