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Lens Luxation mutation FOUND!!

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Late in 2011 - University of Missouri, College of Veterinary Medicine

Spinocerebellar Ataxia with Myokymia & Seizures in Jack/Parson/Russell Terriers

Since the mid 1990s, we have been studying a constellation of movement disorders in Jack/Parson/Russell Terriers. The situation is complicated because there appear to be several different forms of the disease in the breeds.

What is spinocerebellar ataxia?

The term cerebellum in Latin means “the little brain”.  The cerebellum is the part of the brain responsible for coordinating movements.  Ataxia comes from a Greek term meaning “without order”.  When the cerebellum cannot coordinate movement, the dog can move, but the movement is poorly coordinated.  They are not weak, in fact, often the movements a dog with ataxia makes are too strong.  They have a goose-stepping gait and when excited or running, their legs may appear to be going every which-way. Sometimes they have problems with their balance and will fall frequently.  In order for the cerebellum to control movement, it needs to get feedback about what the muscles are doing.  This feedback comes to the brain through the spinal cord.  When there are changes in the spinal cord in a dog with cerebellar ataxia, the disease is often call spino-cerebellar ataxia (SCA).

Ataxia refers to poor coordination of movements.

A dog
with ataxia has exaggerated movements which can cause
frequent falls.

What is myokymia?

Myokymia is a problem with the muscles (myo- in medical terms). Dogs with this symptom have uncontrollable twitching of the muscles. The twitching tends to run through a muscle in waves, hence the –kymia portion of the word which comes from the Greek word for waves. Attacks of myokymia can be precipitated by exercise or excitement. The severity can vary from mild muscle twitching to incapacitating attacks. When severe, the dog can become rigid and develop a high body temperature. Such severe attacks can be confused with seizures, but the dog remains aware of his surroundings during an attack of myokymia. Some dogs with spinocerebellar ataxia also have true seizures.

What are the different forms of ataxia in Jack/Parson/Russell Terriers?

There appear to be at least two different forms of cerebellar ataxia in these lines, a neonatal cerebellar ataxia and a later onset of ataxia (spinocerebellar ataxia or SCA) with or without myokymia or seizures. In the neonatal form the dogs have ataxia from the time they begin to walk. The age of onset is similar to the disease in Coton de Tulears, but they are caused by different genes.

In spinocerebellar ataxia, the dogs develop normally for the first few months of life. Then beginning at 2-6 months of age they begin to develop ataxia. Thus spinocerebellar ataxia is also called "late onset" cerebellar ataxia though the onset still occurs in fairly young dogs. There could still be other forms of ataxia as well.

What else can look like spinocerebellar ataxia?

In addition to the neonatal ataxia, other diseases can cause signs of ataxia. Any disease that affects the cerebellum will produce ataxia. Canine distemper infections will frequently affect the cerebellum as can other infections. Though strokes are uncommon in dogs, they can also affect the cerebellum. In older dogs, a brain tumor in the cerebellum would produce similar signs. If necessary, your veterinarian can refer you to a board certified neurologist who can aid in diagnosing the cause of ataxia. A directory to a neurologist near you can be found at www.acvim.org under "Search for a Specialist".

Is this a hereditary disease?

Further research is needed, but the pedigrees analyzed thus far suggest that SCA is inherited as a recessive trait. In a recessive disease, both parents of an affected pup appear normal. All animals have two copies of each gene, one that is inherited from the mother and one inherited from the father. A dog that has one normal gene and one gene that causes the disease is a carrier of the trait. They show no symptoms because the one good gene is enough for their nerves and muscles to develop normally, but they will pass that bad gene on to about half of their offspring. If a carrier dog is bred to another carrier, then some of the pups (25% on average) will get a bad gene from each parent. Without one good gene to carry the day, the nerves cannot function normally and the unlucky pup has SCA.

CGD home
The Canine Genetic Diseases Network is a group of researchers dedicated to eliminating genetic disease in dogs

Is there a DNA test?

In 2012, researchers at the University of Missouri found the mutation responsible for spinocerebellar ataxia in Jack/Parson/Russell Terriers. Researchers at the Animal Health Trust in England may have also found this same mutation. A DNA test is now available and can be ordered through the Orthopedic Foundation for Animals website (www.offa.org).

Owners of dogs previously sampled for this or other research projects, or with DNA banked at Missouri for any reason can request a discounted test by using the request form found at this link – (click here), or contact Liz Hansen at HansenL@missouri.edu for a print version. With the DNA test carriers of the mutant gene can still be used for breeding as long as they are bred to a dog that is clear of the mutation. That way no affected dogs will be born, but the desirable genetic diversity that these dogs provide the breed will be maintained. When selecting future breeding stock, the gene status can be considered in deciding which pups to keep but does not have to be the sole factor. As discussed above there are other both hereditary and acquired causes of cerebellar ataxia. Thus not every dog with ataxia will have the mutation.

September 1, 2009  University of Missouri, College of Veterinary Medicine

PLL - Primary Lens Luxation of the eye

A mutation responsible for the development of lens luxation in many breeds of dogs has been identified by a team of researchers led by Gary Johnson DVM PhD at the University of Missouri College of Veterinary Medicine. A DNA test for this mutation is expected to be available by late September 2009 through a partnership with OFA (Orthopedic Foundation for Animals).

Lens Luxation is an eye problem well known in many Terrier breeds, Chinese Cresteds , Australian Cattle Dogs, Tibetan Terriers, and other breeds. The lens is held in place in the eye by fibers known as zonules. If these zonules break or disintegrate, the lens can fall out of place, or luxate. When this happens it often requires immediate veterinary attention to remove the displaced lens. Lens luxation can cause secondary glaucoma, which also leads to pain, loss of vision, and sometimes loss of the entire eye.

Research at the University of Missouri has led to identification of a DNA mutation that predicts which dogs are at risk for developing lens luxation as they age. A simple DNA test will reveal if a dog is NORMAL (has 2 normal copies of the gene), a CARRIER (has one normal copy and one mutated copy of the gene) who will not develop lens luxation but could pass the mutation on to offspring, or AFFECTED/AT RISK (has 2 mutated copies of the gene). Wise use of this test gives breeders a tool to avoid producing individuals at risk of developing lens luxation, while still retaining many other desirable traits in their dogs.

Breeders and individual owners will be able to test their dogs using the testing kit that can be ordered online through the OFA website (www.OFFA.org). DNA is collected using a cheek swab, and the barcoded sample will be tested by the Animal Molecular Genetics Lab at the University of Missouri, with results reported directly to the owner by OFA.

Owners who had submitted samples for research prior to Sept 1, 2009 may request test results for their dogs using this Test Request Form for existing samples click here for this form.

Owners of dogs that have been diagnosed as affected with lens luxation by an ACVO or ECVO boarded ophthalmologist are eligible to receive a free DNA test if they send a blood sample, pedigree copy, and a copy of the ophthalmologist's report – click here for the instructions and form to submit samples from affected dogs. Samples from affected dogs may be sent now as well.

Testing for all other dogs is available through OFA. 

Our thanks to the clubs and many individual owners who have supported this research and participated in the project by supplying samples and information on their dogs, as well as monetary support. We also greatly appreciate support from the Jack Russell Terrier Club of America, and past support from the Canine Health Foundation for the early stages of this research. Please watch this space for updates in the next few weeks. If you have questions, you may contact Project Coordinator Liz Hansen at HansenL@missouri.edu.

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