Mutations in unfolded protein response regulator ATF6 cause hearing and vision loss syndrome
Activating transcription factor 6 (Atf6) is a key regulator of the unfolded protein response (UPR) and is important for endoplasmic reticulum (ER) function and protein homeostasis in metazoan cells. Patients carrying loss-of-function ATF6 disease alleles develop the cone dysfunction disorder, achromatopsia.  The impact of loss of ATF6 function on other cell types, organs, and diseases in people remains unclear. Here, we reported that progressive sensorineural hearing loss was a notable complaint in some patients carrying ATF6 disease alleles and that Atf6-/- mice also showed progressive auditory deficits affecting both genders.  In mice with hearing deficits, we found disorganized stereocilia on hair cells and focal loss of outer hair cells.  Transcriptomic analysis of Atf6-/- cochleae revealed marked induction of UPR, especially through the PERK arm.  These findings identify ATF6 as an essential regulator of cochlear health and function.  Furthermore, they supported that ATF6 inactivation in people causes progressive sensorineural hearing loss as part of a blindness-deafness genetic syndrome targeting hair cells and cone photoreceptors.  Lastly, our genetic findings support ER stress as an important pathomechanism underlying cochlear damage and hearing loss with clinical implications for patient lifestyle modifications that minimize environmental/physiologic sources of ER stress to the ear. Overall design: In light of the broad range of organs impacted by a loss of ATF6 in experimental animal models, we investigated whether patients lacking functional ATF6 had additional diseases or phenotypes beyond the previously reported vision loss. We also characterized the cellular and molecular defects in the ear that underlie the hearing loss in the Atf6-/- mice.