Overview
RVED is an autosomal recessive inherited form of vitamin E deficiency. Severe vitamin E deficiency leads to the accumulation of pigment granules (lipofuscin) in multiple tissues of the body including muscle, the reproductive tract, the brain and in the eye. In the eye, the granules accumulate in the retina and are associated with retinal degeneration and visual deficits which, left untreated, can lead to complete blindness. Some dogs with RVED also have neurological problems.
Until now, RVED, could only be diagnosed by referral to a veterinary ophthalmologist and documentation of typical pigmented spots in the retina followed by a blood test to demonstrate low circulating blood vitamin E concentration. This DNA test allows the identification of the RVED mutation and treatment of cocker spaniels with RVED before they develop signs of disease. Cocker spaniels with two copies of the RVED mutation will develop retinal disease (and possibly neurological signs) if not treated and should have their blood tested for vitamin E deficiency by a veterinary surgeon. If vitamin E deficiency is confirmed, then twice daily oral administration of an appropriate dose of vitamin E usually restores vitamin E levels to the normal range and should halt progression of retinal and brain disease. Regular monitoring of blood vitamin E levels (at least every 6 months) is advised longterm.
The 102bp deletion in the gene called TTPA that causes Retinopathy with Vitamin E Deficiency in Cocker Spaniel is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop General disease during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop General disease as a result of the TTPA mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop General disease should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the TTPA mutation (i.e. carry no copies of the mutation). If a carrier is mated to a clear dog approximately half of the resulting puppies will also be carriers, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Retinopathy with Vitamin E Deficiency, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.
