Mice heterozygous for the deafness gene have normal auditory thresholds

Cochlear degeneration in the early postnatal period has been reported as a homozygous recessive mutation in deafness (dn/dn) mice of the curly-tail stock. Heterozygous (+/dn) mice of the same population exhibit hearing when tested by the Preyer reflex, and their cochlear morphology appears normal by light microscopy. However, whether the heterozygote's unmatched recessive deafness allele has deleterious effects not detected by this reflex has not been examined. This study compares the ABR thresholds of presumed homozygous dominant (+/+) and known heterozygous (+/dn) deafness mice, as well as CBA/J mice. Hearing thresholds in the heterozygotes were not significantly different from those of presumed homozygotes or CBA/J mice. A 'generational backtracking' method was used to increase the probability of identifying homozygous (+/+) animals of the curly-tail strain.