PIK3CA and Alzheimer disease: Contrary to initial expectations, an overactivation of PI3K signaling was reported in postmortem brain tissue in both immunohistochemistry and immunobiochemistry with an increase in Akt activation, a loss of neuronal cytosolic Akt and a loss and modified localization of PTEN in the temporal cortex and hippocampus of AD patients (Griffin et al., 2005).