SLOUGHIS AND PROGRESSIVE RETINAL ATROPHY

By Timothy Anderson PhD, Ermine Moreau-Sipiere, and Karin Schirmer

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Dogs, just like humans, have many Genetic disorders. Common in breeds other than the Sloughi are genetic disorders such as cardiovascular problems, displasia, and epilepsy. Until recently, the Sloughi has had no known genetic disorders. Unfortunately, the genetic disease called progressive retinal atrophy (PRA) has now appeared in Sloughis in Europe and the United States, probably through spontaneous mutation or introduced by North African Sloughis.

What is progressive retinal atrophy?

The retina lines the back of the eye and contains photoreceptors which consist, in dogs as in humans, of rods and cones to detect dim light (rods) and bright light (cones). In diseased (affected) dogs, these cells deteriorate (atrophy) over a period of time with rods usually deteriorating before cones. The final result is blindness. PRA is common in many, many dog breeds and the rate of vision deterioration is not the same in all breeds. In Sloughis, vision begins to be affected at about age 2 and progressively deteriorates to age 4 or older.

Because PRA is a genetic disease, let's review the relevant background

Genetic information is carried by chromosomes contained in the nucleus of every living cell making up an organism. Chromosomes consist of DNA, a helical chain of molecules which codes the genetic information needed for the growth, development, and maintenance of a living organism. A gene is that portion of DNA which is the basic unit of inheritance. A gene gives instructions for (codes for) a specific molecule (a protein or polypeptide) and, thereby, determines some aspect of growth, development, and/or maintenance. Different forms of the same gene are called alleles. As in other sexually reproducing animals, a dog has two copies (a pair) of each gene, with one copy coming from the mother and one copy from the father. A parent contributes only one-half of its own genes to its offspring. The two copies in a pair of genes may not be the same allele. When the two alleles are different, the dominant allele gets expressed and the other allele is called recessive and has no expression. Recessive expression occurs only if both alleles in the gene pair are recessive for that characteristic.

In all of the many dog breeds affected, PRA seems to be a simple recessive trait and a monogenetic trait. That is, a single gene pair is responsible and the normal allele of the gene is dominant while the PRA-causing allele is recessive.

As a simple recessive trait, PRA will appear in offspring only if both parents contribute an allele causing (positive for) PRA. If only one parent contributes a PRA-positive allele, the offspring will be a carrier, but will not develop the disease. Obviously, the genetic makeup of the parents is critical to what is passed on to the offspring. A normal parent can contribute only a normal allele, a carrier parent can contribute either a normal or a PRA-positive allele, and an affected parent can contribute only a PRA-positive allele.

The chart below shows how a simple recessive trait is inherited from normal, carrier, and affected parents.

Much of the distribution in offspring, of a simple recessive trait as shown by the chart is statistical. That is, probably more than four offspring are necessary in order to get the illustrated proportions of normal, carrier, and affected offspring from affected-carrier, carrier-carrier, and carrier-normal parents. The chart is based, of course, on the pioneering genetic work by Mendel in the 19th century.

What do we do about PRA in Sloughis?

To remove PRA quickly from the Sloughi's genetic makeup, no affected (diseased) Sloughis should be bred and we should try to avoid breeding carriers. The problem is not inherent in the breed, but runs in family lines. By controlling the family lines, we have the opportunity to eliminate PRA from our Sloughis.

If selected carriers are bred, they should only be bred to normal Sloughis. In that way, no affected (diseased) Sloughis can result and normal offspring are maximized. All resultant offspring should be tested (more about testing below) and carrier offspring should be sterilized before having the opportunity to breed, never be bred, or be bred only under exceptional circumstances. The sterilized or non-breeding offspring will still be wonderful companion dogs and will not develop the disease.

Why would we want to breed carriers? There can be compelling reasons. Many have desirable genetic characteristics which we wish to preserve in Sloughis, so we should breed carefully to pass the desirable traits on to normal offspring. There are too few Sloughis in America and Europe to discard numerous good traits in order to eradicate immediately one bad, but recessive, characteristic. Nevertheless, whenever possible, breeding should be between normal Sloughis.

We are very, very fortunate that a genetic test has been developed for Sloughis. All that is needed is a blood sample from a Sloughi of any age. The test indicates if the Sloughi is normal, a carrier, or affected. The test is reasonable in cost. Information about testing in the United States can be found at www.optigen.com. Sloughi breeders in the United States and Europe are testing all of their breeding stock in order to try to eliminate PRA in Sloughis within the next two to four generations. Any individual owner of a Sloughi which might be used for breeding should have the dog tested as soon as possible. Genetic diseases caught before wide dissemination can be eliminated from a breed. We should strive to eliminate PRA in Sloughis out of our respect and love for these wonderful dogs. How quickly will depend upon the still-to-be-determined prevalence of the PRA allele in the Sloughi breeding stock.

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Addresses:

USA:

OptiGen, LLC
Cornell Business Technology Park
767 Warren Road, Suite 300
Ithaca, New York, 14850
Tel: (607) 257-0301
Fax: (607) 257-0353
E-mail: genetest@optigen.com
For shipping samples, forms payments
please visit: www.optigen.com

Germany:

Department of Molecular Human Genetics:
Molekulare Humangenetik, Geb. MA5.
Universitatsstr. 150. Bochum, 44780 Germany.
Tel: 49 - 234-32-23839
Fax: 49 - 234-32-14-196
Website: http://mhg.uni-bochum.de

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Aknowledgements:

Special thanks to:
Professor Nicola Lopriemo, Molekular-Genetic (Italy),
Gabriele Dekomien, Ruhr-Universitat, Bochum (Germany),
and Dr. Jahangir Sadeghi, M.D (U.S.).

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References:

King, Judy, Simple Recessive Chart, JP Teez Akita Website
(http://www.natural-akita.com/JPTeez/home.html).

English Springer Spaniel Field Trial Association,

Recessive Gene Inheritance Patterns, ESSFTA Website
(http://www.essfta.org/index.htm).

The Boys Town Research Registry for Hereditary Hearing Loss,
1988,Autosomal Recessive,Inheritance,Boystown
Website: (http://www.boystown.org/btnrh/deafgene.reg/recessiv.htm).

Genentech, 1998, Recessive and Dominant Inheritance,
Bioweb Graphic Gallery (http://members.tripod.com/geneticweb/recessive.html).

Acland, Gregory, 1995, PRA, Background and Diagnosis, Sheepdog-L
Website: (http://www.sheepdog.com/diseases/pra/back.html).

Kai-La-Sha, Catherine Marley, Progressive Retinal Atrophy,
etPets Website (http://www.netpets.com/dogs/healthspa/pra.html).

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© Ermine Moreau-Sipière and Erika N. Walsh. These pages, together with all the text, graphics and photographs within them are copyrighted by the American Sloughi Association and may not be reproduced without expressed, written permission.