HTLV-1 infection can lead to the development of an aggressive CD4+ T-cell malignancy, adult T-cell leukemia/lymphoma (ATL) (2–4), or a neurological disorder called HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP) (5, 6). The gene discussed is CD4; the disease is tropical spastic paraparesis.