Part of the official UK Kennel Club testing scheme in Boston Terrier, French Bulldog and Staffordshire Bull Terrier
Cataracts are a leading form of blindness in the dog. Cataracts associated with an HSF4 insertion appear early in life, within the first few weeks or months of life. The cataracts will progress to total blindness by 2-3 years of age and the only effective treatment is a surgical intervention.
The single nucleotide insertion in the gene called HSF4 that causes Hereditary Cataracts in Staffordshire Bull Terriers, Boston Terriers and French Bulldogs is autosomal recessive. This means that dogs that carry two copies of the mutation (homozygotes) will almost certainly develop Hereditary Cataracts during their lives. Dogs that carry a single copy of the mutation (also known as carriers or heterozygotes) will not develop Hereditary Cataracts as a result of the HSF4 insertion mutation, but they will pass the mutation onto about half of any offspring they have. Breeding dogs that will not develop Hereditary Cataracts should be the breeder’s priority, with a reduction in mutation frequency within the whole breed being the secondary, longer-term target.
Carriers can be bred from safely, provided they are mated to a dog that has also been tested and is clear of the HSF4 insertion 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, so should be tested themselves prior to breeding. Breeding carriers to tested, clear dogs is safe, in terms of avoiding dogs affected with Hereditary Cataracts, and will help to maintain the genetic diversity of a breed. It is therefore encouraged, particularly in the first few generations following the availability of a new genetic test, so that other desirable characteristics and traits can be preserved before the frequency of the disease mutation within the breed is gradually reduced.