After a long period of clinical latency, HTLV-1 infection leads, in a fraction of infected individuals, either to Adult T-cell Leukemia/Lymphoma (ATLL) [4], an uncontrolled CD4+ T–cell proliferation of very poor prognosis, or to an inflammatory disorder named HTLV-1 Associated Myelopathy / Tropical Spastic Paraparesis (HAM/TSP) [5]. The gene discussed is CD4; the disease is adult T-cell leukemia/lymphoma.