Reduced VDR activity enhances the expression of the APP, BACE1, and PSEN1 genes and increases the production of Aβ42, which directly or indirectly activates GABAB1R/CaSR heterodimers to increase cAMP production and enhance the expression and phosphorylation of Tau, leading to PTH hypersecretion and the manifestations of hyperparathyroidism. This evidence concerns the gene PSEN1 and hyperparathyroidism.