Though a mutation in CHST6, presumed to lead to the absence of sulfation of KS precursors, is established as the cause of MCD, the presence of sulfated epitopes that are recognizable by the 5D4 monoclonal antibody in the cornea and/or serum of a subset of MCD patients suggests a further level of complexity in the pathogenesis of MCD. This evidence concerns the gene CHST6 and macular corneal dystrophy.