Cataract is one of the most common hereditary problems in Australian Shepherds and certainly the most common heritable eye disease of this breed. Typical clinical sign is opacity of the crystalline lens which leads to blindness. Primary/inherited form of the disease is found in around 100 dog breeds, but despite its frequency the genetic basis is poorly understood. To date only HSF4 gene was associated with hereditary cataracts in dogs and is also responsible for the development of the disease in Australian Shepherds, , Boston Terriers, Staffordshire Bull Terriers and French Bulldogs.
Inheritance of the disease is relatively complex due to its autosomal dominant mode and incomplete penetrance, which means that not all heterozygous animals develop the disease. Clinical manifestation varies considerably. Pathological changes develop on different parts of the lens, onset of the disease varies from young adulthood to brink of old age, and progression of the disease is also very variable. These facts indicate that other yet unknown genetic and environmental factors contribute to disease development. According to the scientific literature the probability of developing the disease is 17 times higher in HSF4 heterozygous animal comparing to HSF4 clear animal. The test cannot exclude other genetic defects which may be involved in the development of hereditary cataract in Australian Shepherds.
In Boston terriers, Staffordshire Bull Terriers and French Bulldogs we can find two kind of hereditary cataract. Early-onset hereditary cataract (EHC) affects dogs within few weeks of age, is always progressive and bilateral, and results in total blindness. Late-onset hereditary cataract (LHC) usually affects dogs over the age of 3 years and is more variable in its clinical phenotype, age of onset, progression, and the degree to which vision is impaired. The mutation in HSF4 gene has been reported only in dogs affected with EHC.
Inheritance: autosomal dominant (incomplete penetrance) - Australian Shepherd - read more;
autosomal recessive - Boston Terrier, Staffordshire Bull Terrier and French Bulldog - read more.
Mutation: HSF4 gene
Genetic test: The method used for testing is extremely accurate and allows complete differentiation between affected animals, carriers and healthy dogs. Testing can be done at any age.
Australian Shepherd: Because disease is autosomal dominant with incomplete penetrance it will manifest itself in most of animals carrying at least on mutated gene. Such heterozygous animals will show clinical signs which will decrease their quality of life. With the intention of eradication of the disease it is not advisable to breed affected and carrier animals.
Other breeds: read more
Sample: EDTA whole blood (1.0 ml) or buccal swabs. Detailed information about sampling can be found here.