Consistent with that relationship, a similar higher level of SM deacylase activity was detected in the epidermis from AD skin (Figure 15), whereas there was no significant difference in levels of aSMase between AD skin and HC skin [50], which suggests that epidermal cells from AD patients show abnormal production of the hitherto undiscovered epidermal enzyme termed SM deacylase. Here, SMPD1 is linked to Alzheimer disease.