HTLV-1 infection is associated with two major diseases: a malignancy of mature CD4+ T-cells named adult T-cell leukemia/lymphoma (ATLL), and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP), with 1–5% of infected individuals developing related diseases [3]. The gene discussed is CD4; the disease is adult T-cell leukemia/lymphoma.