Its main symptoms include high fever, loss of weight, hepatomegaly, splenomegaly, cachexia, anemia, leukopenia, thrombocytopenia, hypergammaglobulinemia (2, 3), and the progressive suppression of the T CD4+ cellular immune response, which comprises both the decrease of the total CD4 T-cell counts (6–9) and the decrease of the CD4 Leishmania-specific T-cell responses (10–12). The gene discussed is CD4; the disease is Splenomegaly.