Here we demonstrate that a signaling lymphocyte activation molecule (SLAM) family of receptors, CD244, was overexpressed on CD8+ T cells of HTLV-I-infected patients than those of healthy normal donors, and that the upregulation of the adaptor protein, SAP, in CD8+ T cells distinguished HTLV-I infected individuals with and without neurologic disease. This evidence concerns the gene SH2D1A and nervous system disorder.