Please read this if you are a rat
terrier owner. This is important to all rat terrier owners and
very critical if you are a breeder.
Only recently (this was
written in 2010) we became aware
that some of our rat terriers carried a genetic disease called
Primary Lens Luxation (PLL). A few of our puppy owners contacted us
because their rat terrier had developed glaucoma. While it was
upsetting to learn that some of our dogs carried PLL, I am very
grateful that I was made aware of the problem. If they hadn't
contacted me I wouldn't have known there was an issue since none of
my own dogs have ever developed glaucoma. That is why it is so
important to notify your dog's breeder if an issue comes up. Even if
you aren't sure it's genetic, it is still a good idea, since issues
in a given bloodline can be traced if they are reported.
If a rat terrier you got from us
develops glaucoma please let us know. It could help us identify
other dogs that may be at risk. If your dog comes from our lines,
please let us know the test results if you get your rat terrier
If you are wondering if your rat
terrier might be at risk for developing PLL please contact us. We
might be able to tell you. We are now testing all our rat terrier
breeding stock. We also know the status of a few of the dogs in our
dog's pedigrees. Obviously all litters from here on out will be
Below we have compiled
information from around the web that is very useful.
Here is a link to
OFA's website where the PLL test can be ordered.
Order OFA PLL test
What is PLL?
"Lens luxation is the dislocation or displacement of the lens within
the eye. The lens is the clear structure in the eye, consisting of
two rounded or convex surfaces, that focuses light rays to form an
image onto the retina. Normally the lens is suspended between the
iris (the colored portion of the eye) and the vitreous (the clear
gel in the back of the eye), and is held in place by small fibers
called zonules or suspensory ligaments.
Should the zonules break, the lens can either become partially
dislocated (subluxated) from its normal position or completely
dislocated (luxated). When the lens detaches and falls forward into
the anterior chamber in front of the pupil, it is called an anterior
luxation. When it falls back into the rear portion of the eye, it is
called a posterior luxation."
"Primary lens luxation is an inherited disorder in which the
zonules or suspensory fibers degenerate. The condition occurs mainly
in the terrier breeds, namely the Parson Russell terrier, Tibetan
terrier, smooth fox terrier and rat terrier. Primary luxations are
also seen in the border collie, the Australian cattle dog (blue
heeler), and sporadically in other breeds. Although the underlying
reasons for the lens luxation are not well understood, inflammation
or a defect in the zonules may play a role. With primary lens
luxations, both eyes are prone to dislocation of the lens. "
SOURCE: PET PLACE - CLICK HERE
Please check out these links for
Canine Lens Luxation Basics
A DNA Test for Primary Lens Luxation is Available
Until October 15, 2009 there was NO test for PLL. Breeders were
having to breed in the dark. But NOW, we have the tool we need to
eliminate this disease from our bloodlines. The
University of Missouri, College of Veterinary Medicine through the
OFA (Orthopedic Foundation for Animals), now has a DNA test for
The DNA test can determine a dogs PLL status as:
"AFFECTED have 2 mutated copies of the gene. The vast majority of
these dogs will luxate at 4-8yrs of age, the typical age of onset
for PLL. There were a few dogs in the study group that tested as
AFFECTED but did not luxate until after 8 yrs of age, and some dogs
testing AFFECTED have died from other causes without luxating. A
search of published veterinary literature revealed that about 10% of
the dogs reported to be clinically affected with PLL had onset of
symptoms after 8 yrs of age. Because of this, the test results will
say �AFFECTED/HIGH RISK�.
"Dogs testing CARRIER are at a slight risk of developing PLL.
Carriers have one normal and one mutated copy of the gene. They
could pass either the normal copy or the mutated copy on to their
offspring. Because there were very few cases of dogs in the research
groups testing CARRIER who did appear to have PLL, the test results
will say �CARRIER/LOW RISK�.
"A dog testing NORMAL has 2 normal copies of the gene, is not at
risk for developing PLL, and can only pass a normal copy of the gene
to any offspring."
Dogs that have been determined as carriers and normal can be bred
Autosomal Recessive Diseases
"This finding indicates that the gene is not present in your dog.
Therefore, when used for breeding, a Clear dog will not pass on the
"This finding indicates that one copy of the disease gene is present
in your dog, but that it will not exhibit disease symptoms. Carriers
will not have medical problems as a result. Dogs with Carrier status
can be enjoyed without the fear of developing medical problems but
will pass on the disease gene 50% of the time."
"This finding indicates that two copies of the disease gene are
present in the dog. Unfortunately, the dog will be medically
affected by the disease. Appropriate treatment should be pursued by
consulting a veterinarian."
* Please Note: Some sites and some breeders use the word Normal
or Clear. Both these words mean the same thing. It means that
the dog in question is NOT a Carrier nor is it Affected.
Sometimes you will see the wording "Cleared By Parentage" or "CBP".
This means both sire and dam are proven Normal/Clear and that
pair bred together can never produce an affected or a carrier.
Helpful Canine Breeding Chart
Autosomal Recessive Diseases
"The chart provided below outlines the implications of various
breeding pair combinations. Remember, it is always best to breed
"Clear to Clear". If followed by all breeders, these strategies will
ensure a significant reduction in the frequency of the targeted
disease gene in future generations of dogs. However, to maintain a
large enough pool of good breeding stock, it may be necessary for
some breeders to breed "Clear" to "Carriers" (see below)."
"Ideal Breeding Pair
- Puppies will not have the disease gene (neither as Carrier
nor as Affected)."
Breeding Is Safe
- "No Affected puppies will be produced. However, some or
all puppies will be Carriers. Accordingly, it is recommended
that Carrier dogs which are desirable for breeding be bred
with Clear dogs in the future, which will produce 50%
carrier and 50% clear animals, to further reduce the disease
gene frequency. These offspring should be tested for this
defective gene, and if possible, only the clear animals in
this generation should be used."
High Risk Breeding
- Some puppies are likely to be Carriers and some puppies
are likely to be Affected. Even though it is possible that
there will be some clear puppies when breeding "Carrier to
Carrier", in general, neither this type of breeding pair nor
"Carrier to Affected" are recommended for breeding.
Breeding Not Recommended
- "All puppies will be genetically and medically affected."
SOURCE: VetGen Breeding Strategies
"Our research has also demonstrated that the frequency of the PLL
mutation is extremely high in the PLL-affected breeds that we have
studied in depth. This means that allowing only CLEAR dogs to breed
could have a devastating effect on breed diversity and substantially
increase the likelihood of new inherited diseases emerging.
Therefore, we strongly advise breeders to consider all their dogs
for breeding, regardless of their PLL genotype. GENETICALLY AFFECTED
and CARRIER dogs can be bred with, but should only be bred to DNA
tested, CLEAR dogs. All puppies from any litter that has at least
one CARRIER parent should be DNA tested, so that the CARRIERS can be
identified and followed clinically throughout their lives. This
practise should be followed for at least one or two generations, to
allow the PLL mutation to be slowly eliminated from the population
without severely reducing the genetic diversity of breeds at risk."
Source:Animal Health Trust
Here is a link to OFA's website where the PLL
test can be ordered: Order
OFA PLL test