CLDN9, also known as claudin 9, belongs to the claudin family. CLDN9 is expressed in the inner ear, olfactory
epithelium, and anterior pituitary gland and is involved in hearing. CLDN9 creates charge specific channels in the
paracellular space, plays a major role in tight junction-specific obliteration of the intercellular space, through
calcium-independent cell-adhesion activity, is required to preserve sensory cells in the hearing organ because CLDN9-defective tight junctions fail to shield the basolateral side of hair cells from the K+-rich endolymph. Its ion
barrier function is essential in the cochlea, but appears to be dispensable in other organs. Is one of the entry
cofactors for hepatitis C virus; it enables HCV entry into target cells just as efficiently as CLDN1.