Hereditary cataract (HC)

Cataract is an eye disorder affecting the lens transparency. Cataracts are very often inherited and occur in more than 70 dog breeds. In connection with the hereditary forms of cataracts in dogs, there have been described several modes of inheritance, the majority being autosomal recessive. There are also autosomal dominant or polygenic modes of inheritance. Cataracts are the leading cause of blindness in dogs.
The hereditary cataracts are often called primary cataracts. Secondary cataracts are forms of a cataract that accompanies other eye disorders, for example, progressive retinal atrophy, glaucoma, retinal dysplasia, metabolic diseases and other disorders. The cataracts may develop after an eye injury (traumatic cataracts) or are related to ageing (senile cataracts).
The cataracts are very specific in individual breeds with regard to the affected parts of the lens, age of disease onset, progression rate and the rate of bilateral development of the cataract.
In Australian Shepherds, a mutation of deletion 1 bp in exon 9 of HSF4-gene (Heat shock factor protein 4) has been discovered in relation with HC (Mellersh et al. 2009).
The presence of deletion mutation is significantly associated with the development of binocular cataracts at various ages. The HC disorder in Australian Shepherds has an autosomal dominant mode of inheritance, however with incomplete penetrance. It means that the disease may not develop in every carrier of this deletion and effects of other genetic factors or environmental factors are not excluded. The probability that the binocular HC develops in individuals with one copy of deletion (carriers) is approximately 17 times higher than in dogs clear of the deletion mutation (Mellersh et al. 2009). The carries of the mutation pass it on to their offsprings and therefore, it is necessary to avoid mating two heterozygous dogs as 25 % of puppies born will be homozygous.
A test does not exclude presence of other mutation of HSF4 gene or other genes responsible for hereditary cataracts in dogs that have not been published or known yet.

.