APP and cancer: These expression vectors, with or without the glycosyl-phosphatidylinositol (GPI) anchor, could be used as tools for (a) studying the effects of mutation on HGprt enzyme found from different LND/LNVs patients; (b) studying the emerging role of HPRT1 gene in cancer, especially exploring the effects for the surface expression of HPRT1 gene; (c) exploring the mechanism linking HGprt deficiency, purinergic pathways, and neural dysfunction of LND; (d) exploring the structure and the physiologic function of APP; (e) studying intermolecular interactions between APP and HGprt enzyme.