PSEN1 and neurodegenerative disease: Because we have previously reported that HPRT deficiency leads to several aberrant signaling defects in common with those found in Alzheimer's disease, as in the case of dysregulated presenilin-1 and Wnt/β-catenin signaling in HPRT-deficient fibroblasts [6], we applied the Panther Classification System to examine the microarray transcriptome data for GO terms related to neurodegenerative disease (Table 7).