What are the genetic changes related to Christianson syndrome ?
Christianson syndrome is caused by mutations in the SLC9A6 gene, which provides instructions for making a protein called sodium/hydrogen exchanger 6 (Na+/H+ exchanger 6 or NHE6). The NHE6 protein is found in the membrane surrounding endosomes, which are compartments within cells that recycle proteins and other materials. The NHE6 protein acts as a channel to exchange positively charged atoms (ions) of sodium (Na+) with hydrogen ions (H+). By controlling the amount of hydrogen ions, the NHE6 protein helps regulate the relative acidity (pH) inside endosomes, which is important for the recycling function of these compartments. The NHE6 protein may have additional functions, such as helping to move proteins to the correct location in the cell (protein trafficking).  Mutations in the SLC9A6 gene typically lead to an abnormally short NHE6 protein that is nonfunctional or that is broken down quickly in cells, resulting in the absence of functional NHE6 channels. As a result, the pH in endosomes is not properly maintained. It is unclear how unregulated endosomal pH leads to neurological problems in people with Christianson syndrome. Some studies have shown that protein trafficking by endosomes is important for learning and memory, but the role of endosomal pH or the NHE6 protein in this process has not been identified.