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Miniature bullies suffer with all the same generic illnesses as standard bullies plus primary Lens Luxation (PLL), All is not lost if your dog becomes affected as the use of Xalatan drops is proving successful in saving the sight of our mini's. And now with a DNA test to give us the true status of our mini's eyes we should never breed another affected again - read on for further information.


What is PLL

A diagram of the canine eye so that you can understand how it works.


Primary Lens Luxation (PLL)

PLL is a serious condition affecting the eyes of Miniature Bull Terriers (Bull Terriers are NOT affected by this disease).


A DNA test is available for Miniature Bull Terrier breeders which tells us the status of the dog be it clear of the PLL mutation, Carrier of the PLL or affected by PLL. It means that no affected puppies should be born in the future and this disease can be eventually wiped out forever. Any puppy buyer should ask for proof of the puppies PLL status either from the puppies DNA test result or both parents DNA test result, if no proof can be offered its best to walk away, buying a puppy from breeders or puppy sellers with no proof (ignore all excuses) will only encourage them to continue breeding without testing first. The Animal Health Trust or OFA are by far the best place to have a DNA test conducted  as results from other laboratories particularly in Europe have proved to be questionable, the DNA test was designed by both the AHT & OFA so they are the people who have the correct procedures to conduct this test. Nobody should be breeding an affected puppy today, if you are considering a carrier puppy bear in mind that the only problem you are likely to encounter in the future is with breeding when you can only use a certified Clear dog or bitch in the breeding program & it is advised that you have yearly eye checks just to be sure, however yearly eye checks on all breeding dogs whatever the PLL status is advisable to be sure they are not suffering from any other eye abnormality. Further information is available below but I think some history on PLL will help newer people understand the disease and why the DNA test is such an important and valuable tool.


Information on how to & where to do the DNA test can be found on the AHT website Here



With PLL affected dogs the Zonules (string like substance holding lenses in place) deteriorate over time and eventually break, this allows the lenses to move freely in the eye. In many cases the lenses slip forward and this is when the real danger begins. The lenses block the eyes natural drainage channels and pressure builds up in the eye, this is known as secondary glaucoma. It is this pressure build up that can cause serious damage to the dogs sight and is often painful and uncomfortable. If your dog shows signs of discomfort in its eyes (continued scratching/ay rubbing or the eyes look in any different to normal) then you should seek veterinary advice immediately and if there is any doubt take your dog straight to an ophthalmologist. Serious eye damage can occur quickly and within a matter of hours so urgent treatment is required. Without treatment your dog could become blind and whilst an operation to remove the lenses can take place, mini bulls do not tend to recover well (believed to be due to the deep set eye) and very often full eye removal is necessary.


Prior to the DNA test being available the only way of knowing if the dog was affected was when the clinical signs presented themselves. Regular eye checks by an ophthalmologist using specialist equipment would often detect the very early signs of the lenses wobbling and Xalatan eye drops could be administered to attempt to prevent the lens moving forward and causing pressure build up. Our own dog Tiffany was lucky enough to have the condition caught at the early stages (thanks to regular eye checks) and has now been on Xalatan drops for 4 years with no need to remove her lenses or eyes!! She can still see although it is more restricted than normal but she lives a perfectly happy life with enough sight to move around without difficulty. Her eyes are checked on a 3 – 6 monthly basis to ensure everything is where is should be!


Xalatan drops are the same medication used for people with glaucoma. They reduce the pressure in the eye and also restrict the pupil, for minis with PLL this helps prevent the lenses moving forward and thus prevents pressure build it. Xalatan and similar medications have been used successfully on minis for many years now and prevented many dogs having to go through an operation or risk of needing full eye removal.


PLL is a late onset disease which for breeding (before the DNA test became available) was a nightmare. Clinical signs very rarely showed themselves before a dog was 3 years old and often not until 4 or 5 years and even 6 to 7 years old. Therefore many dogs affected by PLL where bred from without anyone knowing they had the problem. Due to this PLL became widespread in the breed and was a constant battle for breeders. The KC allowed breeders to interbreed, that is allowed a Bull Terrier to be mated to a Mini Bull Terrier. Because Bull Terriers never suffered with PLL breeders could be sure they were ‘clear’ of the disease and mated to a mini meant that no matter what the minis status was, the offspring would only ever at worse be carriers of the disease. This helped breeders immensely and allowed more clear blood to be introduced to the mini breed. Of course, in some cases this caused larger dogs to be produced but each breeder had to weigh up the risks of producing PLL or having a slightly bigger mini!


The PLL gene is inherited in a recessive fashion, that is 2 copies of the mutant gene must be present in affected dogs. This means dogs can be either clear of PLL (no copies of the mutant gene), carriers of PLL (have one copy of the mutant gene and one clear gene) or affect by PLL (2 copies of the mutant genes). Below is an example of how the gene can be passed on.


Each pup receives one gene from its mother and one gene from its father therefore for the below combinations can occur, remember one gene is taken from father and one gene from mother so for each mating there is 4 outcomes possible.


PP = Clear dog

Pp = Carrier dog

pp = Affected dog


PP x PP = PP, PP, PP, PP (all puppies will be clear)


PP x Pp = PP, PP, Pp, Pp (each puppy has a 50% chance of being clear and a 50% chance 

                                          of being a carrier)


Pp x Pp = PP, Pp, Pp, pp (each puppy has a 25% chance of being clear, 50% chance of

                                         being a carrier and a 25% chance of being affected)


Pp x pp = Pp, Pp, pp, pp (each puppy has a 50% chance of being a carrier and 50%

                                        chance of being affected)


pp x pp = pp, pp, pp, pp (all puppies will be affected)

Noting the above combinations of mating's, a carrier or affected dog can be mated to a clear dog and no affected puppies will be produced. This is an important point to remember now that DNA testing is available. It means carriers or affected can still be used in breeding programmes safely and knowing no affected puppies will be produced. It means breeders have a larger choice, an important thing in a breed with a very small gene pool.


PLEASE ensure your dog is DNA tested by the AHT prior to mating so you can be sure what their PLL status is and make an informed decision on what dog you should use. If ALL breeders DNA test then NO affected puppies need ever be born again and this disease will become part of the Mini Bull Terriers history.


If buying a puppy please ASK the breeder for the parents eye status and check the paper work yourself. If a carrier or affected has been mated to a clear then ask for the puppies DNA results or be sure to have the dog DNA tested yourself if you ever decide to breed yourself.


It is still advised to have minis eyes checked yearly by an ophthalmologist, even those tested DNA Clear of PLL due to reports of other eye conditions such as PRA affecting minis.


The Interbreed Program

The UK Kennel Club have allowed the mating of Bull Terriers (BT) to Miniature Bull Terriers (MBT) for many years in the UK to help increase the MBT gene pool as well as improve the health of the breed (mainly in an attempt to reduce PLL) and the quality of dogs. Breeders must be issued a special licence by the KC to allow the registration of puppies by a BT x MBT in order to control the process and ensure that only healthy animals are used, currently to gain a pass the BT must have a clear health certificate for hearing, heart and kidneys and the MBT must have a clear certificate for eyes, heart and kidneys. These health checks must have taken place within the previous 6 months of application and an interbreeding pass is only valid for a 6 month period at a time. Any puppies born by a BT x MBT mating can ONLY be registered as MBT's, regardless to the size, to protect the BT from PLL, a disease they do not currently suffer with.
In 2009 a DNA test was developed to enable MBT breeders to find out if there dogs are clear, carrier or affected - this is discussed above in more detail - and therefore reduce PLL within the breed. Due to this some people have started to question the need for interbreeding however what people must remember is the MBT gene pool is currently extremely small. Recent studies by the KC and AHT showed that the MBT is one of the most highly inbred breeds on the KC records. This is mainly due to breeders being 'scared' to go outside of their own lines due to fears of PLL creeping back in. The work must now begin on increasing the gene pool and breeders must start to widen their searches for good, healthy dogs.
Figures from the AHT in October 2010 showed roughly around 45% of dogs DNA tested in the past year are carriers and about 45% of dogs are clear and the remaining 10% being affected. As all carriers must go to a clear dog this doesn't leave a wide choice. Of the 45% clear dogs many are still to young to use, many are dogs living at home on sofas never to be seen by anyone and many wont pass ALL health tests required before breeding. An educated guess would say of those 45% of clear dogs about 5/10% will be viable for breeding. What this means is that ALL the breeders in the UK (as well as Europe) will seek out those 5-10% of dogs to use. There are many breeders in the UK looking to produce only clear litters so many clear bitches will go to those clear dogs. There are many carrier bitches that must go to those clear dogs. Many people are ignoring the carrier stud dogs for their clear bitches. I am sure the picture is now building up in your mind, it wont be long before we completely bottle neck the MBT and the next generation of minis will all be by the same 3, 4 or 5 stud dogs with no place for anyone to go. If the interbreeding programme is kept going it gives those breeders who wish to use it the chance to find a totally unrelated dog who could provide some much needed 'fresh genes' to our minis.
Does size count? Well of course it does, there wouldn't be a point of a Miniature Bull Terrier otherwise! However, to keep this breed alive breeders have to think much further than their next litter and their next champion. Size may suffer for this but then there are no guarantees. Many MBT x MBT matings have produced very large minis and many BT x MBT matings have produced small minis of 13-14 inches. Breeders of today must PROTECT the breed as a whole and that means keeping the gene pool alive and having a variety to chose from. This means more than producing only small dogs, this means more than producing only clear dogs. We MUST continue to use carrier dogs and continue to allow interbreeding to ensure we keep every option available to increase this already very small gene pool and keeping the MBT going for many more years to come.  So those of you who are lucky enough to have a clear bitch, take some time to consider using a carrier stud dog and let those people with carrier bitches use the clears. This way we keep all options open, it may take you another generation or 2 to get fully PLL clear lines but as long as you are not producing affected dogs then no harm is done.




UK Kennel Club Link to DNA test results


(This gives the results for all mini's tested by DNA by the AHT)


Life after PLL


The Animal Health Trust - Genetics






Written by Debbie Wiles 




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