SP1 and tropical spastic paraparesis: Given that patients with HAM have enhanced HTLV-1 Tax expression compared with ACs and patients with ATL (13, 25), and that HTLV-1 Tax, in cooperation with Sp1, boosts expression of RGMA, it is conceivable that HTLV-1 Tax localizes near the TSS of the RGMA gene at –2916 bp through Sp1, inducing epigenetic priming.