Only 2%–5% of HTLV-1 carriers experience disease: either adult T cell leukemia/lymphoma (ATL), an aggressive form of leukemia characterized by the proliferation of CD4+ T cells, or HTLV-associated myelopathy/ tropical spastic paraparesis (HAM/TSP), an inflammatory disease associated with demyelination of the spinal cord [2,3,4]. This evidence concerns the gene CD4 and tropical spastic paraparesis.