However, HTLV-1 is the etiological agent of a malignant CD4 lymphoproliferation (adult T-cell leukemia [ATL]) [4] and a chronic progressive neuromyelopathy (tropical spastic paraparesis/HTLV-1-associated myelopathy [TSP/HAM]) [5,6]. The gene discussed is CD4; the disease is tropical spastic paraparesis.