ASAH1 and Alzheimer disease: In contrast, in the epidermis of AD skin, it seems likely that the β-subunit is generated both by auto-cleavage of the covalent peptide bond between Ile-142 in the α-subunit and Cys-143 in the β-subunit and by breaking the S-S bond (C31/C340) between the α- and β-subunits of aCDase via unknown mechanisms, which leads to the induction of SM deacylase activity.