ATLL is a rare T-cell malignancy characterized by hypercalcemia, hepatomegaly, splenomegaly, lymphadenopathy, the presence of a monoclonal expansion of malignant CD4+CD25+ T-cells that evolve from a polyclonal population of HTLV-1 infected CD4+ T-cells, and infiltration of lymphocytes into the skin and liver. The gene discussed is CD4; the disease is Splenomegaly.