PDE4A and psoriatic arthritis: Current clinical practice includes several small molecule compounds that target PDE4 for the therapy of lung disease (COPD) (Hatzelmann et al., 2010; Weis and Kobilka, 2018), psoriatic arthritis and plaque psoriasis (Schett et al., 2012) and topically for atopic dermatitis (Callender et al., 2019).