Localization of biotinidase in the brain: implications for its role in hearing loss in biotinidase deficiency

Biotinidase deficiency is an autosomal recessively inherited disorder characterized by neurological and cutaneous features, including sensorineural hearing loss. Although many of the features of the disorder are reversible following treatment with biotin, the hearing loss appears to be irreversible. To better characterize the nature of the hearing loss in this disorder, location of the expression and presence of biotinidase within the brain was examined using Northern blot analysis, in vitro hybridization of a cDNA panel, and immunohistochemical staining. Results indicate low, but detectable expression of biotinidase throughout the brain, but increased concentrations of biotinidase within the dorsal cochlear nucleus, ventral cochlear nucleus, and superior olivary complex of the brainstem, as well as, in the hair cells and spiral ganglion of the cochlea. These findings suggest that biotinidase and possibly biotin plays an important role in hearing.