The roundabout mutation causes hearing and balance defects due to degeneration of cochlear hair cells. Homozyogtes can be identified by 3 weeks of age by their bi-directional circling. They are deaf by 5 weeks of age, the youngest age tested, as assessed by auditory brainstem response measurements.  The deafness is also reflected in the lack of an acoustic startle response. Although the cochlear hair cells are normal at birth, by 7 and 10 days of age a few of the outer hair cells have abnormal hair bundles with degeneration of stereocilla directly adjacent to the kinocillum.  By 15 days of age all outer hair cells have stereocilla degeneration, some completely lacking bundles, and inner hair cells begin to display striking elongation and fusion of stereocillia. By 4 months of age complete degeneration of the organ of Corti and decreased density of spiral ganglion cells is found.

The roundabout mutation causes hearing and balance defects due to degeneration of cochlear hair cells. Homozyogtes can be identified by 3 weeks of age by their bi-directional circling. They are deaf by 5 weeks of age, the youngest age tested, as assessed by auditory brainstem response measurements. Cochlear hair cells are normal at birth, and by 4 months of age complete degeneration of the organ of Corti and decreased density of spiral ganglion cells is found.

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