The UDP-glucuronic acid/UDP-N-acetylgalactosamine transporter (SLC35D1) is an ER membrane-spanning protein that transports nucleotide-sugars from the cytosol into the ER lumen. SLC35D1 transports UDP-GlcUA and UDP-GalNAc, which are substrates for the synthesis of chondroitin sulfate disaccharide repeats, suggesting a role in chondroitin sulfate biosynthesis. Mutations in SLC35D1 can cause Schneckenbecken dysplasia (SCHBCKD; MIM:269250), a rare, autosomal recessive, lethal short-limbed skeletal dysplasia affecting cartilage and skeletal development (Liu et al. 2010, Liu & Hirschberg 2013).