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H. Rah, D.J. Maggs, T. Blankenship, L.A. Lyons; Characterization of a Feline Rod Cone Dysplasia . Invest. Ophthalmol. Vis. Sci. 2003;44(13):533.
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Purpose: A rapid, complete, early-onset retinopathy has been noted in Persian cats. To the authors' knowledge only end-stage inherited retinal degeneration (15 weeks of age) has been described. Our extended pedigree analysis in the preliminary study suggests an autosomal recessive mode of inheritance. Our purpose was to further characterize the inheritance, clinical and histologic features of this disease. Methods: Kittens with known disease genotypes were produced by mating homozygous affected and heterozygous normal carriers. Thirteen cats (5 affected; 8 phenotypically normal carriers) from 3 litters were examined weekly from eye-opening until 16 weeks of age. Assessment of horizontal pupil diameter, pupillary light reflexes (PLR), dazzle reflexes, behavioral testing of vision, slit lamp biomicroscopy, binocular indirect ophthalmoscopy, and fluorescein angiography were performed. Eight enucleated orbits from 2 affected and 4 age-matched carrier cats were assessed histologically. Results: Extent and speed of PLR were diminished in affected cats by 2 weeks of age and decreased further with age in affected individuals. Dazzle reflex was present at eye opening but was lost in affected animals by 3 weeks of age. In some affected animals divergent strabismus was noted. Retinal vascular attenuation was first suspected at 4 weeks of age and affected arterioles and venules equally. Horizontal pupil diameter was greater in affected cats (about 7 mm) than in normal phenotype cats (about 4 mm). This was first noted at 5 weeks. Altered tapetal reflectivity was first observed at 6 weeks of age and was generalized by 9 weeks. At 15 weeks, marked generalized retinal degeneration was seen in all affected cats. Behavioral testing unequivocally confirmed apparent total blindness in affected individuals by 16 weeks of age. Fluorescein angiograms were normal in affected and normal animals. Histological examinations suggest that photoreceptors were present and quickly degenerated between 3 - 15 weeks. Conclusions: We have described an autosomal recessive, rod cone dysplasia of Persian cats. Clinical evidence confirms that disease is present before 3 weeks of age.
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