Cataracts are a leading form of blindness in the dog. Cataracts associated with an HSF4 deletion, specific to Australian Shepherds, usually appear early in life, but can also appear later. The cataracts will progress to complete blindness if the dogs live long enough and the only effective treatment is a surgical intervention. Dogs that carry (have one copy) of the HSF4 deletion are 17 times more likely to develop binocular cataracts than dogs without the variant.
The single nucleotide deletion in the gene called HSF4 that causes Hereditary Cataract in Australian Shepherd is autosomal dominant. This means that dogs that carry one or two copies of the mutation (heterozygotes and homozygotes respectively) will almost certainly develop Hereditary Cataract during their lives. They will also pass the mutation on to all (for homozygotes) or about half (for heterozygotes) of any offspring they have. Breeding dogs that will not develop Hereditary Cataract should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers should not be bred from, even if they are mated to a dog that has also been tested and is clear of the HSF4 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 and will develop Hereditary cataracts caused by the HSF4 mutation during their lifetime.