Notably, PDE inhibitors, such as rolipram for PDE4, sildenafil and yonkenafil for PDE5 (Zhao et al., 2016), and non-selective PDE inhibitors (e.g., ibudilast), have been proposed as potential therapeutic drugs for neurodegenerative disorders, including MS (Pifarre et al., 2011), AD (Myeku et al., 2016; Kumar and Singh, 2017; Rabal et al., 2018; Xu et al., 2018), and PD (Kinoshita et al., 2017; Schwenkgrub et al., 2017). Here, ALDH7A1 is linked to Alzheimer disease.