After many years of preclinical development, two novel PDE4 inhibitors have recently been approved for clinical use in chronic obstructive pulmonary disease (COPD) and psoriatic arthritis (Giembycz, 2008; Spina, 2008; Tenor et al., 2011; Poole and Ballantyne, 2014; Genovese et al., 2015). Here, PDE4A is linked to psoriatic arthritis.