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Caroline J. Zeiss, Gregory M. Acland, Gustavo D. Aguirre; Retinal Pathology of Canine X-linked Progressive Retinal Atrophy, the Locus Homologue of RP3. Invest. Ophthalmol. Vis. Sci. 1999;40(13):3292-3304.
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purpose. To describe the course of photoreceptor disease in canine X-linked
methods. Retinas from 55 dogs (44 males, 8 carrier females, 3 homozygous
females) were obtained by enucleation under general anesthesia. After
fixation and dehydration, tissues were embedded in epoxy resin,
sectioned at 1 μm for light microscopy and stained with azure
II/methylene blue and a paraphenylenediamine counterstain. For electron
microscopy, regions identified by light microscopy were selected and
cut at 60 nm. Sections were stained with uranyl acetate-lead citrate.
Electroretinography from an additional group of normal males, affected
males, and carrier females was performed and the rod and cone responses
results. The earliest lesion detectable by electron microscopy was vesiculation
of rod discs, followed by disruption of outer segments and death of
rods. Loss of cones and progressive atrophy of inner retinal layers
followed. Lesions were most severe in the peripheral retina and
advanced toward the optic disc with disease progression. Significant
variation in disease severity was present in males despite the presence
of the same disease allele in all affected dogs. Carrier females
displayed generalized reduction in photoreceptor density as well as
multifocal areas of complete rod loss. The electroretinogram (ERG)
findings were compatible with the histopathologic abnormalities.
Homozygous females had lesions similar to those seen in affected males.
conclusions. X-linked retinal degeneration is characterized by initial degeneration
of rod photoreceptors, followed by loss of cones and progressive
atrophy of the inner retina. Carrier females display a phenotype
consistent with random X-chromosome inactivation. Variation in genetic
background may alter expression of the disease allele in affected
animals, thus accounting for variation in phenotypic expression of the
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