Arylsulfatase A(ARSA) hydrolyzes cerebrosidesulfate to cerebroside and sulfate. ARSA is inhibited by phosphate. The phosphate develops a covalent bond with the active site 3-oxoalanine. ARSA gene defects cause metachromatic leucodystrophy(MLD), a progressive demyelination disease which results in various neurological symptoms and ultimately death.