Just browsing and found this article.  Not sure how old the article is but thought it quite interesting reading....

Thanks to a breakthrough by scientists at the Animal Health Trust, in Newmarket, hereditary cataracts in Staffordshire Bull Terriers may become a thing of the past.

Many pedigree dogs, it appears, are predisposed to one or more of the many hereditary diseases that affect our canine friends. As an example, Staffordshire Bull Terriers are particularly susceptible to hereditary cataracts. The condition manifests itself at a young age, usually about 3 months, and is always bilateral (affecting both eyes) and progressive. This means that eventually, and usually by 18 months to 2 years of age, dogs with this condition will become completely blind. Breeders' have long been aware of this problem and have done their best to avoid breeding from affected dogs. However, their efforts have been hampered by the fact that many dogs can be 'carriers'. Such animals do not show any clinical signs of the disease but, unfortunately, they can pass it on to their offspring. Now, however, thanks to a major scientific breakthrough by scientists working at the Animal Health Trust in Newmarket, it will soon be possible to reduce the incidence, and ultimately to eliminate hereditary cataracts in this breed by selective breeding.

Dr Cathryn Mellersh and the genetics team at the Trust have identified the specific genetic mutation that causes the problem and they have established that all clinically affected dogs (those that show clinical signs) have 2 copies of this mutation whereas carriers have just one copy. It is therefore possible to identify, without doubt, all dogs that are capable of passing on the disease.

Interestingly, this does not necessarily mean that carriers should not be used for breeding. Dr Mellersh explains 'If a carrier is bred with another carrier, there is a 25% chance of any offspring being clinically affected, a 25% chance of them being genetically clear and a 50% chance of them being a carrier. However, if a carrier is bred to a clear dog (one without any copies of the gene mutation), 50% of the offspring will be clear and 50% will be carriers. Therefore carriers can be used for breeding, without any danger of producing clinically affected puppies, providing all breeding animals are tested and combinations of dogs that could produce affected puppies are avoided.

This will be a great relief to Staffordshire Bull Terrier breeders as it is possible that up to 20% of the breed in the UK will prove to be carriers. Dr Keith Barnett, Consultant in Ophthalmology at the Trust, emphasised the importance of using this information to ensure safe breeding selections. He commented "not only is it safe to use carriers for breeding purposes, we would actively encourage breeders to do so. The alternative approach, of not breeding at all from any carriers, would result in a severe depletion of the gene pool and this may well result in an increase in other genetic abnormalities".

The initial work on this project was funded early in 2003 by the Kennel Club Health Foundation and the Staffordshire Bull Terrier Breed Council. The first stage involved the analysis of a random selection of about 350 genetic markers from the canine genome to look for patterns of inheritance that were similar to that of the disease within a large extended pedigree of dogs with hereditary cataracts. In order to do this, over 100 DNA samples were supplied from affected dogs and their close relatives. This required a great deal of co-operation from the breeders themselves and the Trust is enormously grateful to all those who participated in the project.

In the second stage, and with funding from the American Kennel Club, Dr Mellersh looked at specific genes which are known to be associated with hereditary cataracts in the human population. The geneticists looked at 20 candidate genes in 10 affected and 12 carrier dogs. One particular gene showed a clear pattern of inheritance that suggested it was involved with the development of hereditary cataracts. They determined the DNA sequence of this gene in affected, carrier and clear dogs, subsequently identifying the mutation responsible for the disease. This was a relatively simple exercise largely because the entire dog genome had recently been sequenced and made available to scientists across the world.

'We were left in no doubt' said Dr Mellersh, 'Every single affected dog we studied had 2 copies of this mutation and every carrier had just one copy. As a result of this breakthrough, the Trust has now developed a diagnostic screening test which will be able to identify accurately those dogs which are affected, carriers or clear'. This is the first genetic screening test for identification of any hereditary cataract in the dog.

The DNA test for hereditary cataracts in Staffordshire Bull Terriers is not yet available, but the AHT hopes to be offering it in the near future. When we do we will publicise the test through the dog press and this web-site.