Pendred syndrome is an autosomal recessive disorder characterized by 
sensorineural hearing impairment, presence of goiter, and a partial defect in 
iodide organification, which may be associated with insufficient thyroid hormone 
synthesis. Goiter development and development of hypothyroidism are variable and 
depend on nutritional iodide intake. Pendred syndrome is caused by biallelic 
mutations in the SLC26A4 gene, which encodes pendrin, a transporter of chloride, 
bicarbonate and iodide. This review discusses the controversies surrounding the 
potential role of pendrin in mediating apical iodide efflux into the lumen of 
thyroid follicles, and discusses its functional role in the kidney and the inner 
ear.