However, some Slc9a6 mutant variants causing Christianson syndrome in humans do not significantly alter the ion exchange properties of NHE6 (Ilie et al., 2020; Ilie et al., 2019) suggesting that Christianson syndrome could be caused by loss of NHE6 scaffolding functions and not by loss of endosomal pH regulation. Here, SLC9A6 is linked to Christianson syndrome.