Treatment of Familiar Lymphohistiocytosis

Inclusion Criteria : * Patient \< 18 years * Patient with diagnosis of hemophagocytic lymphohistiocytic syndrome confirmed by at least one of the following two criteria : * Genetic diagnosis FHL or other genetic disease predisposing to HLH like Chediak-Higashi syndrome, Griscelli syndrome type II and X-linked lymphoproliferative syndrome type I and II (XLP-1 and XLP-2) or positive family history of HLH * Presence of at least 5 of the following 8 criteria (diagnostic criteria as defined by the "Histiocyte Society" ) : * Fever * Splenomegaly * Cytopenia (affecting at least two cell lineages : Hemoglobin \<9.0 g / dl, Platelets \<100.000/μl, Absolute neutrophil count (ANC) \<1.000/µl) * Hypertriglyceridemia and / or hypofibrinogenemia (Fasting triglycerides ≥ 3 mmol / l, Fibrinogen ≤ 1.5 g / l) * Haemophagocytosis found in a histological specimen (without evidence of a malignant process and rheumatic disease) * Decreased or absent NK function (\<10% of the laboratory standard) * Ferritin ≥ 500μg / l * Soluble CD25 ≥ 2.400U/ml or presence of activated T cells in the immune phenotyping * Patient without prior specific treatment of lymphohistiocytic activation syndrome or under treatment with corticosteroids and / or ciclosporin. * Patient beneficiary of a health insurance scheme * Holder (s) of parental authority who signed the informed consent * Man or woman in reproductive age willing to take reliable contraceptive measures during the treatment and 6 months…