The human deafness-pigmentation syndromes, Waardenburg syndrome (WS) type 2a, 
and Tietz syndrome are characterized by profound deafness but only partial 
cutaneous pigmentary abnormalities. Both syndromes are caused by mutations in 
MITF. To illuminate differences between cutaneous and otic melanocytes in these 
syndromes, their development and survival in heterozygous Microphthalmia-White 
(Mitf(Mi-wh) /+) mice were studied and hearing function of these mice 
characterized. Mitf(Mi-wh) /+ mice have a profound hearing deficit, 
characterized by elevated auditory brainstem response thresholds, reduced 
distortion product otoacoustic emissions, absent endocochlear potential, loss of 
outer hair cells, and stria vascularis abnormalities. Mitf(Mi-wh) /+ embryos 
have fewer melanoblasts during embryonic development than their wild-type 
littermates. Although cochlear melanocytes are present at birth, they disappear 
from the Mitf(Mi-wh) /+ cochlea between P1 and P7. These findings may provide 
insight into the mechanism of melanocyte and hearing loss in human 
deafness-pigmentation syndromes such as WS and Tietz syndrome and illustrate 
differences between otic and follicular melanocytes.