A previous study attributed an activating role to 2B4 in HTLV-1 infection due to high SAP levels, the study demonstrated a significantly higher SAP expression in HAM/TSP individuals compared to asymptomatic carriers although data was only shown for HAM/TSP (a subgroup of HTLV-1 manifestation) and AC subjects. Here, SH2D1A is linked to tropical spastic paraparesis.