Sulfatase modifying factor 1 is responsible for the posttranslational modification of a highly conserved cysteine residue to a unique formylglycine residue in the active site of the STS enzyme that is crucially required for catalytic activity; changes in sulfatase modifying factor 1 impact on STS activity with human inactivating mutations resulting in multiple sulfatase deficiency (38, 39). The gene discussed is STS; the disease is mucosulfatidosis.