Routine examination for auditory function at 4-5 weeks of age revealed the mutants to be deaf. Acoustic startle response and Auditory brain stem recordings yielded no response at every frequency and intensity tested (click, 8, 16, 32 KHz at 30-90 dB); circling and head tossing behavior can also be observed. Standard pathology work-up on two mutants (428 or 41 days of age) revealed a slight loss of Purkinje cells in the younger mutant. Serial Sections of the ears of the younger mutant showed atrophy in some portions of the organ of Corti. Whole-mount ear exam on the older mutant showed otoconia to be present and no abnormalities. Subsequent characterization in the laboratory of Dr. Kenneth Johnson at The Jackson Laboratory found severe hearing impairment in 6 homozygotes tested at 32 days of age, where ABR analysis showed 35-50 dB threshold elevations relative to controls, and no ABR in 9 homozygotes tested at 70 days of age, even when subjected to the maximum 100 dB stimulus. The Johnson laboratory also performed scanning electron microscopy of mutant cochleae at 30 days of age, showing hair cell bundle abnormalities, and cochlear cross-sections at 6 weeks of age, showing degeneration of the organ of Corti.          


The circling, head tossing, deafness, and organ of Corti degeneration phenotypes of this point mutation are consistent with those caused by the jitterbug allele of this gene.

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