J. smalltlnim. Pract. (1982) 23,763-766.

Progressive retinal atrophy in the Abyssinian cat K . C . B A R N E T T

Unit of Comparative Ophthalmology, Animal Health Trust Small Animals Centre, Lanwades Park, Kennett, Nr. Newmarket, Suffolk

ABSTRACT

Hereditary and progressive retinal atrophy is described in the Abyssinian cat and two cases are recorded in this breed in the United Kingdom. The wide range of age of onset in the cat is discussed and compared with the age incidence of similar conditions in the dog.

I N T R O D U C T I O N

Progressive retinal atrophy (PRA), as an hereditary condition in the dog and showing many similarities to retinitis pigmentosa in man, has been known since the early part of this century. However, reports of hereditary PRA in the cat are rare. Magnusson first described PRA in the dog, in Sweden in 1909 in the Gordon Setter, and called it retinitis pigmentosa. Since that time it has been recorded in many breeds of dog and in several countries. PRA was divided into two forms, gerleralized and central (Barnett, 1965), the former being further subdivided (Aguirre, 1976) into three types, according to whether the rods and/or the cones degenerate prior to maturation.

Advanced generalized retinopathy in the cat, of unknown aetiology, was recorded by Rubin (1963). Retinal degeneration in the Siamese breed was suspected of an hereditary basis (Barnett, 1965), and this aspect has been further studied more recently (Carlile, 1981). An hereditary retinal degeneration in two litters of Persian kittens was described in 1973 by Rubin and Lipton. Feline central retinal degeneration was at first suspected of having an hereditary origin (Bellhorn & Fischer, 1970) but later was proved to be due to deficiency of the sulphur-containing amino-acid, taurhe (Rabin, Hayes & Berson, 1973; Hayes, Carey & Schmidt, 1975; Barnett & Burger, 1980).

It is surprising that there are so few accounts of hereditary retinal degeneration in

0022-45 10/82/1200-0763 $02.00 0 1982 BSAVA

763

764 K. C . B A R N E T T

the cat with the amount of pedigree cat breeding that occurs and the multiplicity of reports of proven hereditary retinal degeneration in the dog. However, Narfstrom (1 98 1) has recorded a generalized form of progressive retinal atrophy in Abyssinian cats in Sweden in which preliminary pedigree studies indicate an hereditary origin.

The purpose of this report is to record PRA in the Abyssinian cat in the United Kingdom.

CASE H I S T O R I E S

Case 1 was a 6-month-old, male, sorrel, Abyssinian kitten (Fig. 1) and the second case a castrated male, 5-years-old, of the usual Abyssinian colouring. Both cats showed advanced signs of generalized PRA with symmetrical changes in the two eyes of greatly increased reflectivity from the tapetal fundus region, indicating retinal thinning, and marked attenuation of the retinal blood vessels; the pupils were dilated with both poor and slow pupillary light reflexes. In Case 2 the reflectivity was more pronounced on either side of the optic disc. Case 1 was re-examined approximately 12 months after the first examination and showed progression of the disease; further narrowing of the retinal vessels had occurred to the point of only ghost vessels being apparent over the tapetum lucidum (Fig. 2). Defective vision of the kitten had been suspected by the owner from as early as 4 months of age; the adult cat was showing signs of blindness for at least 6 months prior to examination.

FIG. 1. Progressive retinal atrophy in an Abyssinian kitten (case 1).

R E T I N A L A T R O P H Y I N A B Y S S I N I A N C A T 765

FIG. 2. The same, one year later, showing further attenuation of the retinal blood vessels.

The diet of both cats was checked and there was no indication of any deficiency, in particular taurine. Neither cat showed signs of systemic or other ocular disease and no secondary cataract was present at the time of examination.

D I S C U S S I O N

Narfstrom (1981) was the first to record PRA as an hereditary condition in the Abyssinian cat, in both Sweden and Finland. She recorded, in the Stockholm area, 19 cases of a bilateral, usually symmetrical, generalized retinal atrophy showing the earliest signs in the tapetal fundus, particularly around the optic disc and at the area centralis, and exhibiting progression and vascular attenuation. In a further communication (Narfstrom, 1982) she recorded 73 cases out of 205 cats examined, both sexes being equally affected and a simple, autosomal, recessive pattern of inheritance was suggested.

The two cases examined in Great Britain were both males and perusal of their pedigrees showed common ancestors, although the parent generations of both were different.

The age incidence of progressive retinal atrophy in the Abyssinian cat is interesting and worthy of comment. Narfstrom’s cases showed the earliest signs at 20 months, the majority occurred between lf years and 2 years of age and were advanced usually before the age of 4. The only other case so far recorded in the United Kingdom (Carlile, 198 1) was first affected at 1 1 years. The cases reported here were 6 months and 5 years. This wide range of age of onset is much greater

766 K. C . B A R N E T T

than the age incidence of generalized PRA of any type in any breed of dog so far described. In the dog the age of onset is typical for the breed with only a narrow range and it is indicative of the type of generalized PRA present in that breed. It is possible that this marked difference between the two species may indicate that more than one type of PRA occurs in the Abyssinian cat.

Further investigation of this feline, hereditary, ocular abnormality is continuing.

R E F E R E N C E S AGUIRRE, G. (1976) Inherited retinal degenerations in the dog. Trans. Am. Acad. Ophthal. Oto-lar.

BARNETT, K.C. (1965) Two forms of hereditary and progressive retinal atrophy in the dog. I. The

BARNETT, K.C. (1965) Retinal atrophy. Vet. Rec. 77,1543-1560. BARNETT, K.C. & BURGER, I.H. (1980) Taurine deficiency retinopathy in the cat. J. small Anim.

BELLHORN, R.W. & FISCHER, C.A. (1970) Feline central retinal degeneration. J. Am. vet. med. Ass.

CARLILE, J.L. (1981) Feline retinal atrophy. Vet. Rec. 108,3 11. HAYES, K.C., CAREY, I. & SCHMIDT, S.Y. (1975) Retinal degeneration associated with taurine

NARFSTROM, K. (198 1) Progressive retinal atrophy in Abyssinian cats. Svensk Veterinartidning, 33

NARFSTROM, K. (1982) Progressive retinal atrophy in the cat. Proceedings ofthe ASVO andISVO,

RABIN, A.R., HAYES, K.C. & BERSON, E.L. (1973) Cone and rod responses in nutritionally induced

RUBIN, L.F. (1963) Atrophy of rods and cones in the cat retina. J. Am. vet. med. Ass. 142,

RUBIN, L.F. & LIPTON, D.E. (1973) Retinal degeneration in kittens. J. Am. vet. rned. Ass. 162,

81,667-676.

miniature poodle. 11. The labrador retriever. Anim. Hosp. 1,234-245.

Pract. 21,521-534.

157, (6), 842-849.

deficiency in the cat. Science, 188,949-95 1.

(6), 147-150.

Las Vegas, Nevada. p. 165.

retinal degeneration in the cat. Znvestve Ophth. 12,694-704.

14 15-1 420.

467-469.