PDE4D and Alzheimer disease: Among the different PDE4 isoforms, PDE4D has been a prominent research focus due to accumulating evidence of its crucial role in cognitive processes, making it this enzyme a promising target for the development of therapeutic interventions in a variety of pathological conditions characterized by memory impairment, such as AD, stroke, and epilepsy (McLachlan et al., 2007; Richter et al., 2013; Bruno et al., 2014; Gurney et al., 2015; Ricciarelli and Fedele, 2015; Wang and Jiang-Ping, 2016).