SerpinB6, also known as Cytoplasmic antiproteinase, Peptidase inhibitor 6, Placental thrombin inhibitor, SERPINB6 and PI-6, is a cytoplasm protein which belongs to the serpin family and Ov-serpin subfamily. SerpinB6 / PI-6 is an inhibitor of cathepsin G, kallikrein-8 and thrombin. It may play an important role in the inner ear in the protection against leakage of lysosomal content during stress and loss of this protection results in cell death and sensorineural hearing loss. SerpinB6 / PI-6 is expressed in keratinocytes (at protein level). It is also found in placenta, cardiac muscle, lung, liver, kidney and pancreas. SerpinB6 / PI-6 is expressed in the inner ear hair cells. It expressed abundantly by normal mast cells in different tissues and by mast cells in mastocytoma lesions. SerpinB6 / PI-6 may be involved in the regulation of serine proteinases present in the brain or extravasated from the blood. Defects in SerpinB6 are the cause of deafness autosomal recessive type 91 which is a form of non-syndromic deafness characterized by progressive and age-dependent sensorineural hearing loss. Vestibular function is normal.