These uncovered enzymatic alterations of aCDase in AD skin also provide a deep insight into understanding the pathogenesis of Gaucher disease, Fabry disease and Niemann–Pick disease where GSP, globotriaosylsphingosine and SPC, respectively, are formed due to deficiencies of BGCase (Gaucher disease), α-galactosidase (Fabry disease) and SMase (Niemann–Pick disease). The gene discussed is GNAS; the disease is Alzheimer disease.