POMC and adenoma: To date, 22 different USP8 mutations have been identified in 129 ACTH-secreting adenomas from 271 patients across three studies (Ma et al. 2015; Perez-Rivas et al. 2015; Reincke et al. 2015; for review, see Perez-Rivas and Reincke 2016), with confirmation of USP8 mutation prevalence in later studies (Hayashi et al. 2016; Song et al. 2016).