FYN and Alzheimer disease: For example, Fyn protein levels are increased in the brain tissue of AD patients, especially in the cerebellum and hippocampus (Zahratka et al., 2017), and the upregulation of Fyn increases the phosphorylation of tau protein on tyrosine-18 and promotes AD progression (Lee et al., 2004), whereas the inhibition of Fyn kinase activity can result in the improvement of synaptic function and memory in mice (Nygaard et al., 2014; Kaufman et al., 2015).