What is Hereditary Cataract in dogs?

Hereditary Cataract is an inherited eye condition in dogs that leads to the clouding of the lens of the eye which can become severe enough to render the affected dog blind. In dogs affected by Hereditary Cataract, there are structural changes to proteins in the eye that lead to a breakdown of tissue in the eye that causes the clouding. This clouded area of the lens prevents the normal passing of light through the affected parts of the lens of the eye onto the retina at the back of the eye. As the cataracts get larger, the greater the loss of clear vision. Not all cataracts are hereditary and can be a result of old age and injury.

Genetics of Hereditary Cataracts in dogs

There is an odd quirk in the genetics of Hereditary Cataracts in dogs. It has a different pattern of inheritance in Australian Shepherds. Other breeds of dogs pass the mutated HSF4 gene to their offspring in an autosomal recessive pattern. This means that an affected dog must have 2 mutated  copies of the HSF4 gene to be affected by Hereditary Cataracts as a normal copy will cancel out the influence of the mutated gene. However, in Australian Shepherds, the mutated gene is dominant so only one copy of the HSF4 gene needs to be present in the dog for it to be affected. This is termed Autosomal Dominant. Although it is dominant, not all dogs with the dominant mutation in this particular case will show any symptoms as it’s dominance is incomplete.

Severity of Hereditary Cataract

Hereditary Cataracts are still considered to be a disease of medium severity even though they do not shorten the lifespan of the affected dog. Hereditary Cataract does however greatly reduce the quality of life of the affected dog from a young age.

What are the symptoms of Hereditary Cataracts in dogs?

The symptoms of Hereditary Cataracts are very similar in all dogs affected but the age of onset, size and progression can vary substantially. Typically, the age of onset is early, at about 1 – 2 years old with some affected Boston Terriers having a later onset than other breeds or even individuals within the same breed. Hereditary Cataracts usually start with a small area of the lens being affected, before they grow to a larger size to possibly take up practically the entire lens area to cause total blindness. The speed of the progression is very variable with cataracts in some dogs growing so slowly that they retain most, if not almost all of their vision, while other will have complete vision loss in a very short time. Hereditary Cataracts affects both eyes but there can be some variance in the condition between the eyes of the same individual.

Diagnosis of Hereditary Cataracts

Diagnosis of cataracts in general can be made by veterinarians performing a basic eye examination. Diagnosing the cataracts as Hereditary Cataracts is usually made based on the age of the affected dog with follow up DNA Disease Screening to confirm the presence of faulty HSF4 genes in the dog.

Treatment of dogs with Hereditary Cataracts

Specialist corrective surgery is sometimes performed to treat cataracts but this is a very expensive treatment that may not always be effective. Many owners of affected dogs choose to help the dog cope with blindness if it occurs as they would if the dog became blind as a result of old age. Dogs affected by Hereditary Cataracts can still live a full life but with some adjustments to their llifestyle.

References

Barnett KC. Hereditary cataract in the dog. J Small Anim Pract. 1978 Feb;19(2):109-20
Bras ID, Colitz CM, Kusewitt DF, Chandler H, Lu P, Gemensky-Metzler AJ, Wilkie DA. (2007) Evaluation of advanced glycation end-products in diabetic and inherited canine cataracts.
Mellersh CS, Graves KT, McLaughlin B, Ennis RB, Pettitt L, Vaudin M, Barnett KC. Mutation in HSF4 associated with early but not late-onset hereditary cataract in the Boston Terrier. J Hered. 2007;98(5):531-3
Mellersh CS, Pettitt L, Forman OP, Vaudin M, Barnett KC. Identification of mutations in HSF4 in dogs of three different breeds with hereditary cataracts. Vet Ophthalmol. 2006 Sep-Oct; 9(5):369-78
Mellersh et al., 2009, Veterinary Ophthalmology 12: 372-378