GJB2 mutations are highly prevalent around the world. The multiple predominant mutations present in different populations attest to the importance of this gene for normal cochlear function and suggests an evolutionary heterozygote advantage. The unusually high carrier rate for truncating mutations among hearing-impaired individuals is consistent with either the presence of complementary mutations or a carrier phenotype. The significant rate of asymmetry and progression highlights the importance of diagnostic workup and close follow-up for this highly variable condition.

An active process in the inner ear expends energy to enhance the sensitivity and frequency selectivity of hearing. Two mechanisms have been proposed to underlie this process in the mammalian cochlea: receptor-potential-based electromotility and Ca 2+ -driven active hair-bundle motility. To link the phenomenology of the cochlear amplifier with these cellular mechanisms, we developed an in vitro cochlear preparation from Meriones unguiculatus that affords optical access to the sensory epithelium while mimicking its in vivo environment. Acoustic and electrical stimulation elicited microphonic potentials and electrically evoked hair-bundle movement, demonstrating intact forward and reverse mechanotransduction. The mechanical responses of hair bundles from inner hair cells revealed a characteristic resonance and a compressive nonlinearity diagnostic of the active process. Blocking transduction with amiloride abolished nonlinear amplification, whereas eliminating all but the Ca 2+ component of the transduction current did not. The results suggest that the Ca 2+ current drives the cochlear active process and support the hypothesis that active hair-bundle motility underlies cochlear amplification.

The microtubule-associated protein tau is found aggregated into paired helical filaments in the intraneuronal neurofibrillary tangle deposits of victims of Alzheimer's disease (AD) and other related dementias. Tau contains a repeat domain consisting of three or four 31-32-residue imperfect repeats that forms the core of tau filaments and is capable of self-assembling into filaments in vitro. We have used high-resolution NMR spectroscopy to characterize the structural properties of the three-repeat domain of tau at the level of individual residues. We find that three distinct regions of the polypeptide corresponding to previously mapped microtubule interaction sites exhibit a preference for helical conformations, suggesting that these sites adopt a helical structure when bound to microtubules. In addition, we directly observe a marked preference for extended or beta-strand-like conformations in a stretch of residues between two of the helical regions, which corresponds closely to a region previously implicated as an early site of beta-strand structure formation and intermolecular interactions leading to paired helical filament (PHF) formation. This observation supports the idea that this region of the protein plays a crucial role in the formation of tau aggregates. We further show that disulfide-bond-mediated dimer formation does not affect and is not responsible for the observed structural preferences of the protein. Our results provide the first high-resolution view of the structural properties of the protein tau, are consistent with an important role for beta structure in PHF formation, and may also help explain recent reports that tau filaments contain helical structure.

The proposed scoring system, which is designed to be easy to use and allow for subjectivity in evaluating obstruction at multiple levels, nonetheless achieves good internal reliability and external validity. Implementing this system will allow for standardization of reporting for sleep endoscopy outcomes, as well as aid the practicing clinician in the interpretation of sleep endoscopy findings to inform site-directed surgical intervention in cases of complicated obstructive sleep apnea.