with Autosomal-Recessive Nonsyndromic Sensorineural Hearing Loss

More than 270 million people worldwide have hearing loss that affects normal communication. Although astonishing progress has been made in the identification of more than 50 genes for deafness during the past decade, the majority of deafness genes are yet to be identified. In this study, we mapped a previously unknown autosomal-recessive nonsyndromic sensorineural hearing loss locus (DFNB91) to chromosome 6p25 in a consanguineous Turkish family. The degree of hearing loss was moderate to severe in affected individuals. We subsequently identified a nonsense mutation (p.E245X) in SERPINB6, which is located within the linkage interval for DFNB91 and encodes for an intracellular protease inhibitor. The p.E245X mutation cosegregated in the family as a completely penetrant autosomal-recessive trait and was absent in 300 Turkish controls. The mRNA expression of SERPINB6 was reduced and production of protein was absent in the peripheral leukocytes of homozygotes, suggesting that the hearing loss is due to loss of function of SERPINB6. We also demonstrated that SERPINB6 was expressed primarily in the inner ear hair cells. We propose that SERPINB6 plays an important role in the inner ear in the protection against leakage of lysosomal content during stress and that loss of this protection results in cell death and sensorineural hearing loss. Genetic causes of hearing loss are estimated to account for 68% of cases in newborns and 55% of cases by the age of four. 1 Autosomal-recessive, dominant, and X-linked inheritance accounts for 77%, 22%, and 1% of the genetic deafness, respectively. 2 Most cases of genetic deafness fall into the category of sensorineural hearing loss and are caused by pathologies of the inner ear or auditory nerves; these can be identified with audiological investigations. Hearing loss can be classified into syndromic (20%–30%) and nonsyndromic (70%–80%) forms based on the presence or