Genetic Defects of the Eye

Which inherited eye defects occur in the Siberian Husky? Although there are many possible eye defects, only three are of current concern in the Siberian. These are hereditary or juvenile cataracts, corneal dystrophy, and progressive retinal atrophy. Each disorder is present in a different portion of the eye, and will occur in any eye color. Eye defects in the Siberian Husky are serious and should not be understated or overlooked.

What are hereditary cataracts & how are they transmitted? Hereditary or juvenile cataracts are manifested by opacity in the lens of a young dog as early as 3 months of age. These cataracts are different from the non-hereditary cataracts affecting aged or senior dogs. The function of the lens of the eye is to focus the rays of light so that they form an image on the retina. An opacity or cataract on the lens causes less light to enter the eye and sight can be diminished. A cataract can cause a mild decrease in eyesight to complete blindness in severe cases. Cataracts can further be classified by location and stage of development. The most common hereditary cataract in the Siberian Husky occurs on the posterior region of the lens. It is not uncommon for a cataract to develop in one eye months before the other eye shows the effects of the disease. Recent DNA research indicates that juvenile cataracts may be carried by a recessive gene. Genetic research is presently under way to develop a simple DNA test to identify dogs and bitches that carry the recessive gene for cataracts.

What is corneal dystrophy? Corneal dystrophy affects the cornea or the outer transparent portion of the eyeball. In most cases, Siberian Huskies with this disorder have an abnormal collection of lipids in the clear cornea of the eye which results in a hazy or crystalline opacity. Ophthalmologists describe the location of the opacity as anterior, mid, or deep stromal. The Siberian Husky is prone to deep stromal dystrophy which involves triglyceride deposits. Annular dystrophy also occurs and appears as a doughnut shaped opacity in the peripheral cornea. Corneal dystrophy is usually seen in young adult dogs and may affect females more than males. Vision is seldom affected and no effective therapy for the condition exists at this time. Recent genetic tests are suggesting that a recessive gene with variant expression transmits this disorder.

What is progressive retinal atrophy (PRA) & how is it transmitted? Progressive retinal atrophy (PRA) affects the retina, the light-sensitive inner lining of the posterior part of the eyeball. The retina contains two types of specialized cells called rods and cones. The rods are necessary for sight in dim light or night light, and the cones are utilized in in bright light vision. The Siberian Husky has a unique type of PRA that is only found in Siberians and man. This type of PRA is called XLPRA (X Linked PRA) since it is transmitted through the "XX" chromosome of the female. It will cause a loss of night vision followed by a loss of day vision, eventually blindness. The recessive gene for XLPRA is situated on the "X" chromosome of the female. Females who inherit a defective gene on the "X" chromosome from one parent and a normal gene on the other "X" chromosome from the other parent, will not be seriously affected. They will be carriers with very subtle retinal defects and no loss of vision. The male puppy from a carrier dam will receive either a defective gene or a normal gene, depending on what chromosome was copied in the DNA replication. If he has the defective gene, the dog will be affected with PRA since males carry an "XY" chromosome. The disease in males can be devastating with loss of vision as early as 5 months of age.

A genetic test available, through Optigen, to identify Siberians that carry this gene or genes, thus this test can help eliminate XLPRA from breeding programs.

How are eye defects diagnosed? Accurate diagnosis of eye defects requires the expertise of a board certified veterinary ophthalmologist who is equipped by knowledge and training to distinguish hereditary eye diseases from non-hereditary eye disorders. The American College of Veterinary Ophthalmologists (ACVO) is the national governing board for the certification of veterinary ophthalmologists. Since 1974, the SHCA has encouraged local breed clubs to support eye clinics, which make eye examination more convenient and affordable to breeders and dog owners. Today, thanks to the devotion and support of local area clubs, eye clinics are common throughout the country and are available to all breeders.

How prevalent are eye defects in the Siberian Husky? Of the three major eye diseases of the Siberian Husky, hereditary cataracts are the most common, followed by corneal dystrophy, and progressive retinal atrophy. A statistical report conducted by members of the American College of Veterinary Ophthalmologists in 1999 provided the following information regarding the Siberian Husky. Out of 1345 Siberian Huskies examined, a total of 107 dogs had inheritable cataracts (8%), a total of 44 dogs had corneal dystrophy (3%), and 4 dogs had progressive retinal atrophy (less than 1%).

How can genetic eye defects be reduced or eliminated? Research is now being conducted to develop DNA testing for both hereditary cataracts and progressive retinal atrophy. Until these tests are available, the SHCA and the American College of Veterinary Ophthalmologists have established guidelines to help breeders decrease the spread of heritable eye disorders. The guidelines are as follows: Every dog to be used for breeding must be examined by a veterinarian that is board certified by the American College of Veterinary Ophthalmology. This examination must be done during the year that the dog is to be used for breeding. Only dogs with normal examinations are to be used for breeding. Caution must be exercised in the use of those dogs that are closely related to affected dogs, or when a breeder suspects that an individual dog is producing a defect in its offspring. Though the dog itself may not exhibit signs of the eye defect, that dog should promptly and permanently be withheld from further breeding.

Is there a breed registry available for normal eyes? Since eye abnormalities can appear over a period of several years, annual eye examinations are imperative. It is possible for a dog to have a normal eye examination at one year of age and be severely afflicted with an eye disorder one or two years later. In the case of hereditary eye disease, consideration must be given to the possibility that the defect occurs as a genetic recessive gene. In this instance, two normal dogs that are carriers of the defect will pass the eye exam and yet pass the genetic defect to the offspring.

In 1975, a central agency was formed to register annual eye examination reports for all breeds. The agency, named the Canine Eye Registry Foundation (CERF), compiled eye data and reports for all breeds. In addition, upon receipt of an approved eye examination form signed by an ACVO veterinary ophthalmologist, the registry issued adult dog certificates and breed numbers which included the date of the eye examination along with the current age of the dog. The certificate was good for one year.

In 1979 SHCA instituted the Siberian Husky Ophthalmologic Registry (SHOR). This agency continued the function of registering Siberian Huskies that had completed an ACVO annual eye examination. In order to receive a SHOR certification, which is only valid for one year, the dog must be at least one year of age. The SHOR registry number consists of three segments:
1. an individual number sequential to the number of previously certified dogs;
2. the month and year of the examination;
3. the age in months of the dog at the examination.
The name of the dog and the registry number are published in the Newsletter of the SHCA, and on this website.

The CERF eye registry disbanded in 2014. The Orthopedic Foundation for Animals established an eye registry in 2013 which is now known as the Companion Animal Eye Registry (or CAER). Both the CAER and SHOR registries are available for eye certification.

Reputable breeders of Siberian Huskies provide current eye examination reports by ACVO veterinary ophthalmologists for all breeding stock. All potential puppy buyers should ask to see the eye examination report for both the sire and the dam of the litter.

The OFA Registry is available at:  www.ofa.org

For SHOR information, contact:

Jamesa Maulden, SHOR Chairperson
PO Box 1611
Chehalis, WA 98532
jamesa@syntari.com
Or, visit the SHOR pages on this website: SHOR