Carbohydrate sulfotransferase 6 (CHST6) catalyzes the transfer of sulfate to position 6 of non-reducing ends of N-acetylglucosamine (GlcNAc) residues within keratan(4)-PG (this represents a keratan chain before sulfation has occured). Keratan sulfate (KS) plays a central role in maintaining corneal transparency. Defective CHST6 results in low- or non-sulfated KS deposited within the intracellular space and the extracellular corneal stroma leading to macular corneal dystrophy, type 1 (MCDC1; MIM:217800). MCDC1 is an early-onset, ocular disease characterized by bilateral, progressive corneal opacification, and reduced corneal sensitivity. Mutations in CHST6 leading to MCDC1 are K174R, D203E, E274K, R211W and L200R as compound heterozygote with C102G, Y110C and L276P (Akama et al. 2000, Aldave et al. 2004).