Overview of the SLC26 family and associated diseases

In the late 1990s the SLC26 family of anion exchangers emerged as the second, structurally distinct gene family capable of similar transport functions as the classical SLC4 or anion exchanger (AE) gene family. The observations leading to the characterization of the SLC26 family were firmly based on research on rare human diseases and aided by comparison to Caenorhabditis elegans. SLC26A1, or rat sulphate/anion transporter 1 (Sat1), was the first gene cloned in mammals, but not characterized in humans until the year 2000. Three rare recessive diseases in humans, namely diastrophic dysplasia (cartilage disorder resulting in growth retardation), congenital chloride diarrhoea (anion exchange disorder of the intestine) and Pendred syndrome (deafness with thyroid disorder) turned out to be caused by the highly related genes SLC26A2 (first called DTDST), SLC26A3 (first called CLD or DRA) and SLC26A4 (first called PDS), respectively. Subsequently, others and our laboratory cloned prestin, a cochlear motor protein gene (SLC26A5), a putative pancreatic anion transporter (SLC26A6), and SLC26A7-SLC26A11. Some SLC26 family members show highly specific tissue expression patterns, others are widely expressed. The SLC26 exchangers are capable of transporting, with different affinities, at least the chloride, iodide, sulfate, bicarbonate, hydroxyl, oxalate and formate anions, and have distinct anion specificity profiles.