AKAP9 mutations had no effect on Aβ40/APP but significantly increased pTau/Tau ratio in LCLs treated with phosphodiesterase-4 inhibitor rolipram, which activates protein kinase A. This study showed the impact of rare functional AKAP9 mutations on Tau, a central mechanism of AD pathogenesis, in LCLs derived from AD and control subjects. Here, MAPT is linked to Alzheimer disease.