(A) Experimental design. CMT1A, CMT1E, and WT C57BL/6J littermates were used. ABRs and DPOAEs were recorded at 1, 2, 3, and 4 months of age, and after the last tests, cochleae were collected and processed for either transmitted electron microscopy or confocal microscopy to evaluate structural changes at the level of the peripheral auditory nerve. (B) ABR waveform illustrating the criteria used to measure ABR peaks. Peak I amplitudes are measured relative to the baseline, while peak II to peak V are measured from the top to the bottom right of each peak, respectively. (C) CMT1A mice have normal DPOAE thresholds at all time points, while CMT1E mice show mild DPOAE threshold shifts starting at 4 months of age. (D) CMT1A mice have normal ABR thresholds while, in CMT1E animals, they are increased at all time points when compared with WT littermates. (E) ABR peak I amplitudes are progressively reduced in both CMT1 groups compared with WT mice; however, these reductions are more severe in CMT1E mice (Supplemental Figure 1). (F) ABR peak I latencies are longer in both CMT1 groups compared with WT mice, yet CMT1E animals show a more severe phenotype compared with CMT1A mice. WT, n = 14–19 mice; CMT1A, n = 8–11 mice; CMT1E, n = 6–12 mice. DPOAE threshold, ABR threshold, ABR peak I amplitude, or ABR peak I latency at each individual time point were evaluated by 2-way ANOVA followed by Tukey’s multiple-comparison test. ABR peak I amplitudes and latencies were measured at 80 dB SPL. **P < 0.01; ***P < 0.001; ****P < 0.0001 versus WT mice; †††P < 0.001; ††††P < 0.0001 versus CMT1A mice. Data are shown as mean ± SEM.