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Electrophysiologic differentiation of homozygous and heterozygous Abyssinian-crossbred cats with late-onset hereditary retinal degeneration

Jennifer A. Hyman DVM, MA1, Vaegan PhD2,3, Bo Lei MD, PhD4,5, and Kristina L. Narfström DVM, PhD6,7
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  • 1 Eye Care for Animals, 11950 W 110th St, Ste A, Overland Park, KS 66210.
  • | 2 Optometry Department, School of Optometry and Vision Science, University of South Wales, Sydney, Australia 2052.
  • | 3 VisionTest, 187 Macquarie St, Sydney, NSW, Australia 2000.
  • | 4 Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.
  • | 5 Department of Ophthalmology, Mason Eye Institute, School of Medicine, University of Missouri, Columbia, MO 65211.
  • | 6 Department of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.
  • | 7 Department of Ophthalmology, Mason Eye Institute, School of Medicine, University of Missouri, Columbia, MO 65211.

Abstract

Objective—To develop a method to electrophysiologically differentiate heterozygous-carrier Abyssiniancrossbred cats from homozygous-affected Abyssiniancrossbred cats before clinical onset of inherited rodcone retinal degeneration.

Animals—14 back-crossed Abyssinian-crossbred cats of unknown genotype (homozygous or heterozygous) for inherited rod-cone retinal degeneration, 24 agematched mixed-breed control cats, 6 age-matched heterozygous Abyssinian-crossbred cats, and 6 homozygous Abyssinian cats.

Procedure—Electroretinography (ERG) of heterozygous and homozygous cats revealed differences, especially for scotopic recordings. Frequent ophthalmoscopy and ERG (2 to 5 times; at intervals of 3 to 6 months) of back-crossed cats were performed. Amplitudes and implicit times were analyzed by use of a graphic representation of results. Ratios for amplitudes of the b-waves to amplitudes of the awaves (b-wave:a-wave) were compared.

Results—8 back-crossed cats had decreased a-wave amplitudes, increased b-wave implicit times, and abnormal ERG waveforms. Values for the b-wave:awave for the highest scotopic light intensity were significantly higher for those same 8 cats.

Conclusions and Clinical Relevance—The 8 back-crossed Abyssinian-crossbred cats with abnormal results developed fundus changes over time consistent with disease. A graphic representation of ERG results can be used to differentiate between genotypes prior to funduscopic changes. Values for the b-wave:a-wave ratio provide confirmation. These ERG analyses may be applied clinically in the diagnosis of retinal degenerations in various species.

Impact for Human Medicine—Cats with hereditary rod-cone degeneration may be a useful model for comparative studies in relation to retinitis pigmentosa in humans. Similar evaluations of ERG results could possibly be used for humans with suspected generalized retinal degeneration. (Am J Vet Res 2005;66:1914–1921)

Abstract

Objective—To develop a method to electrophysiologically differentiate heterozygous-carrier Abyssiniancrossbred cats from homozygous-affected Abyssiniancrossbred cats before clinical onset of inherited rodcone retinal degeneration.

Animals—14 back-crossed Abyssinian-crossbred cats of unknown genotype (homozygous or heterozygous) for inherited rod-cone retinal degeneration, 24 agematched mixed-breed control cats, 6 age-matched heterozygous Abyssinian-crossbred cats, and 6 homozygous Abyssinian cats.

Procedure—Electroretinography (ERG) of heterozygous and homozygous cats revealed differences, especially for scotopic recordings. Frequent ophthalmoscopy and ERG (2 to 5 times; at intervals of 3 to 6 months) of back-crossed cats were performed. Amplitudes and implicit times were analyzed by use of a graphic representation of results. Ratios for amplitudes of the b-waves to amplitudes of the awaves (b-wave:a-wave) were compared.

Results—8 back-crossed cats had decreased a-wave amplitudes, increased b-wave implicit times, and abnormal ERG waveforms. Values for the b-wave:awave for the highest scotopic light intensity were significantly higher for those same 8 cats.

Conclusions and Clinical Relevance—The 8 back-crossed Abyssinian-crossbred cats with abnormal results developed fundus changes over time consistent with disease. A graphic representation of ERG results can be used to differentiate between genotypes prior to funduscopic changes. Values for the b-wave:a-wave ratio provide confirmation. These ERG analyses may be applied clinically in the diagnosis of retinal degenerations in various species.

Impact for Human Medicine—Cats with hereditary rod-cone degeneration may be a useful model for comparative studies in relation to retinitis pigmentosa in humans. Similar evaluations of ERG results could possibly be used for humans with suspected generalized retinal degeneration. (Am J Vet Res 2005;66:1914–1921)