MAPT and Alzheimer disease: GSK3 is a kinase that plays an essential role in AD given its involvement in tau hyperphosphorylation, in our study, no difference was observed in the phosphorylation state of the GSK3β at residue Ser9 in the fibroblasts of FAD patients, although a trend toward reduced phosphorylation at Ser21 was observed for the GSK3α isoform, suggesting an increase in GSK3α activity; accordingly fibroblasts from FAD patients showed higher levels of total GSK3 (Figure 3).