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

Jennifer A. HymanEye Care for Animals, 11950 W 110th St, Ste A, Overland Park, KS 66210.

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 DVM, MA
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VaeganOptometry Department, School of Optometry and Vision Science, University of South Wales, Sydney, Australia 2052.
VisionTest, 187 Macquarie St, Sydney, NSW, Australia 2000.

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 PhD
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Bo LeiDepartment of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.
Department of Ophthalmology, Mason Eye Institute, School of Medicine, University of Missouri, Columbia, MO 65211.

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 MD, PhD
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Kristina L. NarfströmDepartment of Veterinary Medicine and Surgery, College of Veterinary Medicine, University of Missouri, Columbia, MO 65211.
Department of Ophthalmology, Mason Eye Institute, School of Medicine, University of Missouri, Columbia, MO 65211.

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 DVM, PhD

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)