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Richard T. Libby, Karen P. Steel; Electroretinographic Anomalies in Mice with Mutations in Myo7a, the Gene Involved in Human Usher Syndrome Type 1B. Invest. Ophthalmol. Vis. Sci. 2001;42(3):770-778.
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purpose. In humans, mutations in the gene encoding myosin VIIa can cause Usher
syndrome type 1b (USH1B), a disease characterized by deafness and
retinitis pigmentosa. Myosin VIIa is also the gene responsible for the
inner ear abnormalities at the shaker1 (sh1) locus in
mice. To date, none of the sh1 alleles examined have
shown any signs of retinal degeneration. In the present study,
electroretinograms (ERGs) were recorded from sh1 mice to
determine whether they have any physiological abnormalities.
methods. ERGs were recorded from mice homozygous for one of nine mutant alleles
of Myo7a ranging in age from postnatal day (P)20 to
approximately 1 year. All mice were dark adapted for 30 minutes, and
all the mutant mice were paired with an appropriately age- and
strain-matched control animal. A presumptive null allele of myosin
VIIa, Myo7a 4626SB , was used to
determine whether mice without myosin VIIa had an increased threshold,
as assessed by the light level required to elicit a 15-μV b-wave.
results. At the maximum light intensity used, five of the nine alleles examined
had significantly reduced a- and b-wave amplitudes. For example, Myo7a 4626SB mutant mice had a 20%
reduction in a-wave amplitude at the maximum light intensity, and this
reduction was the same for mice ranging in age from P20 through 7
months. The b-wave thresholds of the Myo7a 4626SB mutant mice were not
significantly different from those of the control mice. Furthermore,
whereas most of the alleles’ a-wave implicit times were the same in
mutant and control mice, mutant mice with two of the alleles had
significantly faster a-wave implicit times.
conclusions. Mutations in myosin VIIa in mice can lead to decreased ERG amplitudes
while threshold remains normal. This is the first report of a
physiological anomaly in a mouse model with a mutation in the same gene
as involved in USH1B.
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