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" FACTS ABOUT PROGRESSIVE RETINAL ATROPHY "

( PRA )

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By Leona Domino

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NIGHT-BLINDNESS TEST

RECESSIVE GENE INHERITANCE PATTERN

 

PRA is a general term for a number of eye diseases.

These diseases have included certain features. One is that the diseases begin at a very specific time in each breed.

The diseases progress at a very predictable rate. The dogs that are affected with the disease become blind at an age

very specific to the breed. Some become blind early, some late. The end result is blindness.
 
PAPILLON PRA :

There are a number of different kinds of PRA. PRA can be divided into either dysplastic disease, where the cells develop

abnormally, or degenerative disease, where the cells develop normally but then undergo a damaging change. Usually, dogs

affected with PRA first experience difficulty seeing at night or in dim light. As the disease progresses, the dog is finally

blind both day and night. Papillons are affected with a slowly progressive degeneration that causes blindness at seven to

eight years old. At present there is no cure and no treatment to arrest the course of degeneration in the affected dogs.
 
HOW IS PRA TRANSMITTED ?

PRA IS NOT CONTAGIOUS. It is an inherited disorder, passed along through the generations by a simple autosomal

recessive gene. Simple autosomal recessive inheritance means that if a dog is PRA affected ( is either blind or going

blind ) BOTH of the parents must possess the PRA gene. The dog has inherited the PRA gene from BOTH sire and dam,

giving him a double-dose of the gene. Only when a dog has inherited TWO PRA genes, one from each parents, can he

be actively affected with PRA blindness.
 
The parents of a PRA affected animal may have normal vision themselves, even though they both “CARRY” the

PRA gene. They are referred to as CARRIERS. A carrier shows NO physical signs of possessing the PRA gene.

A carrier has no outward signs that it carries the PRA gene. The way a PRA carrier reveals itself as a carrier is by

producing a PRA AFFECTED ( blind ) offspring.
 
TERMS :

 

AFFECTED

 

:

 

dog has 2 genes that will produce blindness.

( one from each parent )

CARRIER

:

dog has 1 gene and will not produce blindness but can

pass his “bad” gene on to 50% of his offspring.

CLEAR

:

dog has no gene for the disease.

 

 
Dogs have 78 chromosomes and the sex chromosomes are 39 or ˝ of the dog’s genetic picture. When breeding each

parent donates ˝ of its genetic material to the new puppy. Therefore you will note that a carrier will not have signs

of PRA but can continue the disease 50% of the time. If bred to a bitch with the same gene then an affected puppy

can be produced. It takes 2 donated genes to produce affected.
 
WHY ARE CARRIERS OF SUCH CONCERN ?

Since carriers appear normal outwardly, the problem becomes complicated. The situation can be compared to an iceberg.

Blind animals make up the tip of the iceberg that shows, but underneath the surface are the carriers. They cannot be

easily detected as of this date. It is possible for carriers to remain “hidden” in breeding programs before they finally,

if ever, produce an affected puppy. Each time the carrier is used for breeding, a percentage of more "little-carriers"

are added to the breeding population. As time goes on the more carriers there are within a breed, the greater chances

are that affected will ultimately be produced by breeding two "hidden" carriers together.

ARE PRA CARRIERS A BIG PROBLEM IN OUR BREED ?

That is impossible to answer. Since there is no reliable way to identify the carrier status until it reveals itself by

producing a blind puppy, many carriers will never be identified.

WHAT IS BEING DONE TO FIND CARRIERS ?

Research is being conducted at Michigan State University ( Michigan, USA ) to find the marker on the gene that would

result in breeders having a test that would tell them the genetic state of the breeding dog. Dr. Simon Petersen-Jones

is the scientist working on this project. The Papillon Club of America ( PCA ) is assisting with getting a colony of

affected dogs available to the doctor to use in his research.

 


WITH NO TEST AVAILABLE YET, HOW DO I BREED TO AVOID PRODUCING A CARRIER OR AFFECTED DOG ?
Until a test is developed, you can have your dogs examined by a veterinary ophthalmologist , record the finding with

CERF and stay vigilant regarding your dog’s vision. Keep in mind that night blindness or dim night vision is the first sign.

( See : Night Blindness Test below )

 

Do not breed to a dog that has produced an affected puppy or that has not been cleared by an eye exam. Eye exams by

a V.O. should start by 2 years and be yearly until 8-9 years of age.
 
You can give your puppies a night eye test yourself. Keep in mind : very young puppies will show signs of poor night

vision. This may not be visible to the V.O. doctor until 2 to 3 years of age, do the night test on all your puppies.

3-4 month old puppies may show night vision hesitancy. This would be a serious indication of vision problems to come.
  

See test procedure here. It is so simple.

You only need a flashlight and red tissue paper.

  PRINTABLE WORD DOC

THE "NIGHT-BLINDNESS TEST"

An Aid In Detecting PRA

Update of the previous article : Home Testing for PRA

_____________________________________________________

 

A feasible way for most everyone to check for the possibility of Progressive Retinal Atrophy in their

Papillons is a method referred to as "night-blindness test".

  

The properly done electroretinograph is the most definitive method of detecting retinal deficiencies but

a "night-blindness test" will give you an indication of a problem long before an ophthalmoscopic

examination will find signs of disease.

 

I have begun to use this test on my puppies prior to ERG to prove the correlation.  I suggest it to be

performed at 12, 14, and 16 weeks.

 

WE use 2 flashlights using “D” batteries. ( make sure that the batteries are new )  Two thicknesses of

red tissue paper are held in place over the light with a rubber band.  The flashlights are placed at least

5 feet above the floor directing the beam of light to opposite corners of the ceiling.

 

 

The room must be totally darkened … it’s necessary to cover the windows. The flashlights should give

just enough light so that you can observe the dog ( a normal-eyed dog can see well in red light )

therefore, give your eyes time to adjust to the dim light, before proceeding with the test.

 

Prior to turning off the regular lightning,

set-up an obstruction in the center of the room, such as ;

 

~ 2 chairs placed on their sides,

~ a grooming table on its side,

~ 2 waste baskets side by side, or a large carton

 

 

Crate the dog to be tested in a corner of the room.

 

One person will release the dog about 6 feet in front of the obstruction while another person ( well known

by the dog )  calls the dog from behind it.  My experience has been that a normal-eyes dog will around

the obstruction.  Animals affected with a moderate loss of sight will walk up to the obstruction and then

walk around it, while a severely affected dog will walk into the obstruction, usually bumping it solidly.

  

Young puppies ( 12 to 16 weeks ) tend to inquisitive and if they are normal-eyed  will boldly walk up to

the obstruction and check it out, before going around.  They will also, move about the room seemingly

unaware of the lack of the light. Affected pups prefer to remain where you placed them.  One puppy did

come to me after I stepped to the side of the obstruction, continentally talking to her … she crawled into

my feet and sat there crying.

  

The size and color of the testing area will determine the amount of light needed to observe the dogs

behavior, therefore it may be necessary to add more or larger flashlights.  Naturally, a light colored

ceiling will reflect the light more readily than a dark ceiling.

  

All humans present must remain in front of the or directly behind the obstruction, not beside it. 

The obstruction can vary in width from 18 inches to 3 feet with at least 2 feet of space on each side. 

Be awe that the dog is not following a wall.

  

You must be be sure that the dog being tested will respond in a positive manner to the person calling him.

No other words, the dog must know and like the person calling and know how to respond to the word

or words used, such as “come”.

  

Also you may wonder if you are using the proper procedure but, after going through it several times you

will gain confidence.  Do not take the dogs personality into consideration  when you judge the results ...

there is no such room for rationalization.  Instead, have the dogs with inadequate performances

examined by an ophthalmologist and a "proper" ERG, if possible.

 

OPEN THE "NIGHT BLINDNESS TEST" IN A OWN PAGE INCLUDING A PRINTABLE VERSION ( WORD DOC )

 


WHAT OTHER OPTIONS DO I HAVE TO FIND PRA ?
Exciting work is being done regarding "gene-mapping". With present day electronic microscopes and computers DNA

of the body cells are being plotted for many human and dog diseases. Many dog and human problems have been solved

and the PCA is working in this direction with Michigan State to find the PRA gene.

Should you produce a dog with PRA it is important that you are open and share your knowledge. It is only by disclosing

a problem that we can work to eradicate it. Personal ego’s need to defer to scientific discovery. The affected animals

are very valuable and should NOT be hidden. Any breeder admitting to having an affected should be praised and be

recognized for his/her integrity. These people are the role models for our breed.

They are the ones that will help solve the problem and perhaps be the first to eliminate problems from their lines.

Do not rush out and neuter your dog until you verify that the dog cannot be used to further research studies.

The day will come when we can all have our dogs genetic background available.

 

  PRINTABLE WORD DOC   

RECESSIVE GENE INHERITANCE PATTERN

GENETIC CHART

Applicable to GM-1 and PRA

  _________________________________________________________________________________________________________________

NORMAL

  -represent genetic : NORMAL

CARRIER

  -represent genetic : CARRIER

AFFECTED

  -represent genetic : AFFECTED

 

These are only six possibilities for mating.

  Each of our dogs is the product of one of

these six breeding combinations.

 

Both GM-1* and PRA, Progressive Retinal Atrophy,

are recessive genes.

 

This chart can be applied to the

genetic inheritance pattern of each disease.

 

_________________________________________________________________________________________________________________

 

EXPECTED AVERAGE RESULT, BASED ON A MINIMUM OF 16 PUPPIES

PARENTS

OFFSPRING

 

 

Expected average result, based on a minimum of 16 puppies

  Both parents are NORMAL, not carrying the recessive gene.

  100 % of the puppies will be NORMAL.

_________________________________________________________________________________________________________________

PARENTS

OFFSPRING

 

Expected average result, based on a minimum of 16 puppies

  One parent is NORMAL, one parent is CARRIER of the recessive

  gene ... 50 % of the offspring will be NORMAL, 50 % will be

  CARRIERS.

 

  In "Storage" disease Carriers can be detected by a blood assay.

  In PRA, Carriers can not be detected that easily thus pedigree

  analysis is critical

_________________________________________________________________________________________________________________

PARENTS

OFFSPRING

 

Expected average result, based on a minimum of 16 puppies

  An AFFECTED parent will always produce CARRIER offspring.

  In this situation, only 50 % of the offspring will be AFFECTED,

  but the other 50 % will still be CARRIERS.

 

 

  AFFECTED individuals used for breeding automatically identify

  their offspring's as CARRIERS.

_________________________________________________________________________________________________________________

PARENTS

OFFSPRING

 

Expected average result, based on a minimum of 16 puppies

  CARRIER to CARRIER breedings will produce 25 % AFFECTED

  offspring ; 25 % NORMAL offspring ; and 50 % CARRIERS. 

 

  In "Storage" disease, the process of genetic identification has

  been simplified for us. In PRA, the identification of the

  different offspring's genetic make-up is extremely complex.

_________________________________________________________________________________________________________________

PARENTS

OFFSPRING

 

Expected average result, based on a minimum of 16 puppies

  An AFFECTED parent will always produce 100 % CARRIER

  offspring.

 

  AFFECTED parent breed to  NORMAL parent will not produce

  any AFFECTED offspring, but they will all be CARRIERS.

_________________________________________________________________________________________________________________

PARENTS

OFFSPRING

 

Expected average result, based on a minimum of 16 puppies

  AFFECTED parent bred to AFFECTED parent will always

  produce all AFFECTED offspring.

 

OPEN THE "RECESSIVE GENE INHERITANCE PATTERN - GENETIC CHART" IN A OWN PAGE INCLUDING A PRINTABLE VERSION ( WORD DOC )

 

 

 

Andi Meloon

( e-mail : andi2012@centurylink.net )
Chair, Genetic Health Committee
Papillon Club of America

  

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