ALDH7A1 and Alzheimer disease: Higher PME/PDE in AD patients as compared to controls has been reported by 3 studies (Brown et al., 1989; Gonzalez et al., 1996; Forlenza et al., 2005), though 4 studies have reported no differences (Bottomley et al., 1992; Murphy et al., 1993; Smith et al., 1995; Das et al., 2021).