Col1a2 mice exhibit alterations in ossicular bone quality typical of osteogenesis imperfecta but no hearing loss

Osteogenesis imperfecta (OI) is an inherited connective tissue disorder clinically mainly characterized by skeletal fragility. However, non-skeletal manifestations, some of which do not appear until adulthood, can additionally severely impact the health and quality of life of the affected patients. These include hearing loss that is observed in approximately every second OI patient. While the hearing loss in OI is mainly due to impaired sound transmission (i.e., conductive hearing loss), the underlying mechanisms are currently elusive. Here, we investigated the Oim (Col1a2^oim/oim) mouse model of classical OI, focusing on bone quality features of the middle ear and hearing function. No osseous morphological changes were observed in the middle or inner ear of male Col1a2^oim/oim mice compared to wildtype controls. Backscattered electron imaging and Fourier-transform infrared spectroscopy revealed increased matrix mineralization and matrix maturity of the auditory ossicles (malleus, stapes). These changes have previously been described as typical features of OI in other skeletal regions. However, measurement of auditory function by auditory brainstem response revealed no gross hearing pathology and even indicated a slightly improved hearing ability in Col1a2^oim/oim mice in the 32 kHz range as determined by distortion product otoacoustic emissions (DPOAEs). Taken together, our results indicate that the conductive hearing loss observed in classical OI is not due to the altered bone quality of the middle ear, at least under unchallenged conditions in mice.