Carbohydrate sulfotransferase 3 (CHST3 also known as C6ST-1) catalyzes the transfer of sulfate (SO4(2-)) from PAPS to position 6 of the N-acetylgalactosamine (GalNAc) residue of chondroitin-containing proteins resulting in chondroitin sulfate (C6S-PG), a major component of cartilage. Defects in CHST3 result in undersulfated CS, weakening cartilage structures and causing spondyloepiphyseal dysplasia with congenital joint dislocations (SEDC-JD; MIM:143095). Mutations causing SEDC-JD include R304Q, L259P, R222W, L307P, Y201*, E372K and L286P (Thiele et al. 2004, Hermanns et al. 2008, Unger et al. 2010, van Roij et al. 2008).