SLC9A6, also known as NHE6, is a monovalent sodium-selective sodium/hydrogen exchanger (NHE) that is located on the membranes of intracellular organelles such as mitochondria and endosomes. NHEs are involved in a wide array of essential cellular processes, including control of cellular volume and intracellular pH, and reabsorption of sodium across the renal, intestinal, and other epithelia. The dysfunction of SLC9A6 by gene mutations results in an X-linked mental retardation syndrome that is characterized by microcephaly, epilepsy, ataxia, and absent speech and resembles Angelman syndrome.