HINT1 and central nervous system cancer: Of these 8 genes, 6 (SULT4A1 [51], NDRG4 [52, 53], GAP43 [54, 55], BEX1 [56], HINT1 [57], LZTS1 [58]) are believed to act as tumor suppressants, while the remaining two, PKM [59] and VIPR1 [60–62], have been found to be overexpressed in glioma.