Hereditary cataracts (Australian shepherd type) is an inherited eye disease affecting dogs. Cataracts are opacities in the lens of the eye caused by structural changes in lens proteins. A normal lens allows light to pass through it to the Retina in the back of the eye. Light cannot pass through the parts of the lens affected by cataracts and vision becomes blurry. Dogs with Hereditary cataracts (Australian shepherd type) most commonly present between 2 to 7 years of age with small cataracts that are visible on a veterinary eye exam. In dogs that inherit one copy of the Mutation, cataracts develop slowly and on rare occasion, may lead to complete blindness. However, it has been speculated that dogs carrying two copies of the mutation are more likely to develop a more rapidly progressing and severe Cataract. Of note, not all forms of cataracts are inherited and environmental factors such as UV damage can also play a role in the severity of disease. This specific mutation in the HSF4 gene shows Incomplete Penetrance, meaning that not all dogs inheriting two copies of the mutation develop clinical disease. This suggests that other unknown genetic or environmental factors may play a role in modifying disease development and progression.
Breed-Specific Information for the Miniature Australian Shepherd
The miniature Australian shepherd is included as a breed susceptible to Hereditary cataracts (Australian shepherd type) because Australian shepherds are known to develop this disease due to Mutation of the HSF4 gene. The frequency of the causal mutation in the overall miniature Australian shepherd population is unknown. However, in one study of 392 Australian shepherds with and without cataracts from North America and Europe, 25.5% had one copy of the mutation and 3.8% had two copies of the mutation, with an overall frequency of at risk dogs of 29.3%. In this same study, Australian shepherds with this mutation had an approximately 17-fold increased risk of developing cataracts.
Genetic testing of the HSF4 gene in miniature Australian shepherds will reliably determine whether a dog is a genetic Carrier of hereditary cataracts (Australian shepherd type). Hereditary cataracts (Australian shepherd type) is inherited in an Autosomal Dominant manner in dogs meaning that dogs only need to inherit one copy of the mutated gene to be at-risk for the disease. Dogs that inherit two copies of the genetic Mutation are at-risk of developing a more severe form of the disease. Each pup that is born to a parent carrying one copy of the mutation has a 50% chance of inheriting one copy of the HSF4 gene mutation and being at-risk for the disease. If both parents are affected, the chance of having affected offspring increases to 75-100%. Because symptoms may not appear until adulthood and not all dogs with the mutation develop disease, genetic testing should be performed before breeding. Reliable genetic testing is important for determining breeding practices. In order to eliminate this mutation from breeding lines and to avoid the potential of producing affected pups, breeding of known carriers is not recommended. Miniature Australian shepherds that are not carriers of the mutation have no increased risk of having affected pups due to this mutation.
There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.
Mellersh CS, McLaughlin B, Ahonen S, Pettitt L, Lohi H, Barnett KC. Mutation in HSF4 is associated with hereditary cataract in the Australian Shepherd. Vet Ophthalmol. 2009 Nov-Dec; 12(6):372-8.
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.