The incisor absent rat: an animal model for the study of otosclerosis

The incisor absent (ia) rat is introduced as an animal model for the study of otosclerosis. Previous animal models have failed to accurately reflect the dynamic nature of this disease. Auditory brainstem response testing suggested a conductive hearing loss in the incisor absent rat as compared to age-matched normal controls. The hearing loss, which was manifested during puberty, was progressive in nature up to 18 weeks of age. Microscopic dissection of the middle ear revealed bony abnormalities of the ossicles and oval window in the incisor absent rat. Scanning electron microscopy of the ossicles demonstrated bony lesions at the incudostapedial joint and stapes footplate. Histologic examination demonstrated thickened spongiotic bone involving the otic capsule and ossicles. The incisor absent rat model possesses an inheritable defect of the otic capsule and ossicles that results in a progressive conductive hearing loss. The genetically transmitted lesion appears histologically similar to otospongiosis. The bony pathology in the incisor absent rat is caused by defective osteoclasts and transplantation of bone marrow cells from normal rats to the incisor absent rats corrects the cellular abnormality. The incisor absent rat may represent the best animal model to date for the study of otosclerosis, its cause, and clinical treatment.