The Claudin superfamily consists of many structurally related proteins in humans. These proteins are important structural and functional components of tight junctions in paracellular transport. Claudins are located in both epithelial and endothelial cells in all tight junction-bearing tissues. Three classes of proteins are known to localize to tight junctions, including the claudins, Occludin and Junction adhesion molecules. Claudins, which consist of four transmembrane domains and two extracellular loops, make up tight junction strands. Claudin expression is often highly restricted to specfic regions of different tissues and may have an important role in transcellular transport through tight junctions. Claudin-14 is a multi-pass membrane protein that is expressed in liver, kidney and ear. Defects in the gene encoding claudin-14 are the cause of non-syndromic sensorineural deafness autosomal recessive type 29 (DFNB29), a form of hearing loss resulting from damage to either nerve pathways or neural receptors of the inner ear.