Studies suggest that HTLV antibody titers to Gag and Env are significantly higher in HTLV-associated myelopathy/tropical spastic paraparesis (HAM/TSP) patients than in asymptomatic carriers, and antibody titers for Gag, Env, and Tax were higher in HAM/TSP compared to adult T-cell leukemia/lymphoma (ATLL) patients (10, 11). This evidence concerns the gene ERVW-1 and tropical spastic paraparesis.