SLC26A4 and Pendred syndrome: In cases of high plasma I−concentration, there is a decrease in I− uptake and organification, known as the Wolff–Chaikoff effect, which is mediated by a decrease in NIS expression (Eng et al. 1999). The passage of I− into the lumen through the apical membrane of the thyrocyte is carried out by poorly understood transporters such as CLC-5 (Senou et al. 2010), anoctamin-1 (Twyffels et al. 2014), CFTR (Devuyst et al. 1997), and pendrin, named after the Pendred syndrome gene (PDS) (Royaux et al. 2000).