PDE9A and Alzheimer disease: Such investigations take on added significance in light of the fact that high quality PDE9A inhibitors are now available and have entered into initial clinical trials to explore procognitive efficacy in Alzheimer’s disease and schizophrenia (Schwam et al., 2014; Wunderlich et al., 2016; Boland et al., 2017; Moschetti et al., 2018).