PLL is caused by a genetic defect in the zonular (eye) anatomy. This has been found to be an inherited condition in many terrier breeds such as Miniature Bull Terrier, Jack Russell Terrier and the Tibetan Terrier, it is also found in many other breeds.
In an affected the zonules start to break down during the dogs early life (usually 3 to 5 years) resulting in increased movement of the lens. Initially partial disinsertion occurs and eventually it luxates (dislocates) completely.
PLL does not show up until the dog is 3 to 5 years of age and in most cases breeders would have already bred with the dogs.
Our Queensland Tenterfield Terrier club was approached by Dr Carolyn O’Leary (University of Queensland) and Dr Michael Bernaise (Mt Gravatt Animal Hospital) back in 2006 in relation to providing dogs for research work on locating a recessive gene responsible for PLL in our breed. Funding was provided by the University of Queensland in the form of a grant. Around this time a number of Tenterfield Terriers had presented with this disease (affected) Consequently they found a faulty gene (mutated) responsible for the condition and subsequently a DNA test (Bucal cheek swab) has been developed which identifies the mutated gene in puppies as young as four weeks old (providing they are weaned).Unfortunately it has taken a few years to get this stage and now it will take our breeders a few more years of making selective choices to breed it out. With everyone’s help it will happen.
DNA testing (Bucal check swab) has revealed that puppies tested fall into three categories:
- If a puppy acquires the mutated gene from BOTH parents they are GENETICALLY AFFECTED and very highly likely to develop PLL.
- Puppies whose DNA test revealed one mutated gene and one normal gene are classified as CARRIERS. Currently the risk of a CARRIER developing PLL is between 2% and 20%.
- Puppies whose DNA test reveals two normal genes (no mutated genes) are classified as CLEAR and highly unlikely to develop PLL.
DNA testing is not compulsory however the disease can be identified at a much earlier age now, with this testing, it is far less intrusive, less expensive and there is no necessity for a Veterinarian to conduct the test.
What about breeding? The Club strongly recommends that all breeders have their dogs DNA tested before breeding.
GENETICALLY AFFECTED dogs and CARRIERS can be bred but only with CLEAR dogs. All puppies from any litters that have at least one CARRIER parent SHOULD be tested so that further CARRIERS can be identified.
Our pro-active stance in trying to eliminate this disease in our dogs, by selective breeding, also ensures our gene pool will not be affected by careless breeding. And remember breeding CLEAR to CLEAR cannot produce carriers and therefore the progeny are clear by parentage and do not require testing.
The results of DNA testing to date show that this disease is NOT isolated to any particular line or State. It will only be a matter of time before we have blind dogs if breeders fail to test their breeding stock.
This particular genetic disease is detrimental to our breed and at this time, with DNA testing, and selective breeding we can control it and ultimately eradicate it from our breed.
For further information on PLL please check the following websites: