Fig. 3.

Fgfr1^−/−; Fgfr2^−/− mice exhibit progressive hearing loss with age. A: Adult mice were examined for hearing loss by auditory brainstem response (ABR) tests. Hearing sensitivity of individual control and mutant mice is shown as the thresholds of responses to a sound stimulus played at different intensities [in peak equivalent sound pressure level (peSPL), in dB], plotted as a function of age. Overall, mutant mice (solid circles) exhibited higher hearing thresholds than control mice (open circles) at all ages beyond 4 months. B: Mice that showed ABR response to stimuli below 60 dB peSPL were plotted as a percentage of total mice tested in each group. Animals with thresholds below 60 dB were considered to be within the boundary of “normal” hearing. Note the late onset of hearing impairment and progression with age in the mutant mice. Ten to fifteen mice were analyzed in each age group and genotype. Because no obvious differences were observed between males and females, data were pooled for the analysis.