A glucuronate (GlcA) moiety is added to the chondroitin chain by dual-activity enzymes, the chondroitin sulfate synthases 1-3 (CHSY1, CHPF and CHSY3) (Kitagawa et al. 2001, Yada et al. 2003, Yada et al. 2003b). They possess both beta-1,3-glucuronic acid and beta-1,4-N-acetylgalactosamine transferase activity. These three enzymes require divalent metals as cofactors, manganese producing the highest activities. Another candidate enzyme, chondroitin sulfate glucuronyltransferase (CHPF2) possess only beta-1,3-glucuronic acid transferase activity (Izumikawa et al. 2008, Gotoh et al. 2002). Defects in CHSY1 cause Temtamy preaxial brachydactyly syndrome (TPBS) (MIM:605282) (Tian et al. 2010, Li et al. 2010).