EXT1 and neoplasm: Direct evidences from totuvelu (ttv or EXT1 in vertebrates), enzymes involved in HS-chain elongation and modifications, that function as tumor suppressors and implicated in bone overgrowth of humans (Ahn et al., 1995; Stickens et al., 1996) indicate that HS-derived GAG levels are dramatically reduced due to non-functional proteoglycans (Toyoda et al., 2000).