AND PROGRESSIVE RETINAL ATROPHY
By Timothy Anderson PhD,
Ermine Moreau-Sipiere, and Karin Schirmer
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
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
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
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
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
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.
Cornell Business Technology Park
767 Warren Road, Suite 300
Ithaca, New York, 14850
Tel: (607) 257-0301
Fax: (607) 257-0353
For shipping samples, forms payments
Molecular Human Genetics:
Molekulare Humangenetik, Geb. MA5.
Universitatsstr. 150. Bochum, 44780 Germany.
Tel: 49 - 234-32-23839
Fax: 49 - 234-32-14-196
Lopriemo, Molekular-Genetic (Italy),
Ruhr-Universitat, Bochum (Germany),
and Dr. Jahangir
Sadeghi, M.D (U.S.).
King, Judy, Simple
Recessive Chart, JP Teez Akita Website
Spaniel Field Trial Association,
Inheritance Patterns, ESSFTA Website
The Boys Town
Research Registry for Hereditary Hearing Loss,
Recessive and Dominant Inheritance,
Bioweb Graphic Gallery (http://members.tripod.com/geneticweb/recessive.html).
1995, PRA, Background and Diagnosis, Sheepdog-L
Marley, Progressive Retinal Atrophy,
etPets Website (http://www.netpets.com/dogs/healthspa/pra.html).
© 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