PDE4, a cAMP-specific PDE (García-Osta et al., 2012; Li et al., 2018), PDE9, a cGMP-specific PDE, and the dual cAMP and cGMP specific enzymes PDE1 and PDE10 (Reyes-Irisarri et al., 2007) have been reported to significantly expressed in the AD brain. The gene discussed is PDE4A; the disease is Alzheimer disease.