Pendred syndrome is an autosomal recessive disorder defined by sensorineural 
deafness, goiter and a partial defect in the organification of iodide. It is 
caused by biallelic mutations in the SLC26A4 gene, which encodes pendrin, a 
multifunctional anion exchanger. At the level of the inner ear, pendrin is 
important for the creation of a normal endolymph composition and the maintenance 
of the endocochlear potential. In the thyroid, pendrin is expressed at the 
apical membrane of thyroid follicular cells and it appears to be involved in 
mediating iodide efflux into the lumen and/or maintenance of the follicular pH. 
Goiter development and hypothyroidism vary among affected individuals and seem 
to be partially dependent on nutritional iodide intake. In the kidney, pendrin 
functions as a chloride/bicarbonate exchanger. Elucidation of the molecular 
basis of Pendred syndrome and the function of pendrin has provided unexpected 
novel insights into the pathophysiology of the inner ear, thyroid hormone 
synthesis, and chloride/bicarbonate exchange in the kidney.