Susceptibility to Progressive Retinal Atrophy (PRA) in Italian Greyhounds
Progressive retinal atrophy (PRA) is a genetic disease characterized by progressive photoreceptor degeneration that leads to blindness. Mutations in 5 loci are associated with susceptibility to 90% of the PRA in Italian Greyhounds.
Phenotype: Progressive retinal atrophy (PRA) is characterized by progressive degeneration of the photoreceptors in the retina that leads to blindness. On average PRA in Italian Greyhounds is diagnosed at 6.5 years of age.
Mutations in 5 loci are associated with susceptibility to 90% of the PRA in Italian Greyhounds.
Locus A: A = Normal, a = PRA-risk allele
Locus B: B = Normal, b = PRA-risk allele
Locus C: C = Normal, c = PRA-risk allele
Locus D: D = Normal, d = PRA-risk allele
Locus E: E = Normal, e = PRA-risk allele
Breeds appropriate for testing: Italian Greyhound
Explanation of Results:
Dogs with aa or dd genotype are 30 times more likely to develop PRA-IG1 progressive retinal atrophy.
Dogs with Aa/b-/c- genotype (dashes represent either allele) are 9 times more likely to develop PRA-IG1 progressive retinal atrophy (PRA-IG1b subtype).
Dogs with Aa/d-/e- genotype (dashes represent either allele) are 5 times more likely to develop PRA-IG1 progressive retinal atrophy (PRA-IG1c subtype).
Dogs with AA genotype are at low risk of progressive retinal atrophy. Matings between dogs with AA genotype (and without “d” variant) will yield low risk offspring.
Dogs with Aa/BB/CC or Aa/b-/C- or Aa/B-/c- genotype (dashes represent either allele) are at low risk of progressive retinal atrophy, but are carriers that may transmit PRA-risk allele(s) to their offspring.
Dogs with Aa/DD/-- or Aa/Dd/EE genotype (dashes represent either allele) are at low risk of progressive retinal atrophy, but are carriers that may transmit PRA-risk allele(s) to their offspring.
Dog DNA tests are carried out using cells brushed from your dog's cheeks and gums. The preferred cytology brushes are sent to you by mail, or you may provide your own brushes. For accepted alternative brushes, click here
We recommend waiting until puppies are at least three weeks old before testing.
Make sure the dog has not had anything to eat or drink for at least 1 hour prior to collecting sample.
When swabbing puppies, isolate each puppy from the mother, littermates and any shared toys for 1 hour prior to swabbing. Puppies should not have nursed or eaten for 1 hour prior to collecting sample.
If collecting samples from more than one dog, make sure to sample one dog at a time and wash your hands before swabbing another dog.
Label brush sleeve with name or ID of dog to be sampled.
Open brush sleeve by arrow and remove one brush by its handle.
Place bristle head between the dog’s gums and cheek and press lightly on the outside of the cheek while rubbing or rotating the brush back and forth for 15 seconds.
Wave the brush in the air for 20 seconds to air dry.
Insert brush back into sleeve.
Repeat steps 5 - 8 for each unused brush in sleeve on a fresh area of cheek and gums. Make sure to use and return all brushes sent by the VGL. In most cases, it will be 3 brushes per dog. If using interdental gum brushes, please note that the VGL requires 4 brushes per dog and only moderate or wide interdental gum brushes are accepted.
Do not seal brushes in sleeve.
Place all samples in an envelope and return to the address provided.
Do not collect saliva/drool – the key to obtaining a good sample is getting cheek cells on the swab
Do not rub swab on the dog’s tongue or teeth – this will result in poor quality sample
Do not collect a sample from a puppy that has recently nursed – the mother’s genetic material can rub off on the puppy’s mouth and contaminate the sample
Progressive retinal atrophy (PRA) is a genetic disease characterized by progressive degeneration of the photoreceptors in the retina that leads to blindness. There is no treatment for PRA. The incidence of PRA in Italian Greyhounds is 2-4% and it is usually diagnosed at 1 to 14 years of age (6.5 years average). Recent discoveries by University of California, Davis canine researchers Dr. Niels Pedersen and Hongwei Liu identified mutations in 5 loci that are associated with susceptibility to 90% of the PRA in Italian Greyhounds. This form of PRA, designated as PRA-IG1, can be subdivided into 3 subtypes (PRA-IG1a, 1b, and 1c) based on risk genotypes. PRA-IG1a is associated with allele (a) at the major locus that is solely responsible for blindness when in a homozygous state (aa). PRA-IG1b occurs when this allele is in the heterozygous state (Aa) and associated with alleles b and c. PRA-IG1c involves alleles a, d, and e loci in various combinations. PRA-IG1a comprises 42% of PRA cases in the breed, PRA-IG1b 29%, and PRA-IG1c 20%. The frequency of the PRA-risk alleles in the general population is shown in the following table:
Frequency of the normal and PRA-risk alleles in healthy Italian Greyhounds
Total dogs tested
Based on this research, Italian Greyhounds are 30 times more likely to develop PRA-IG1 if they have either 2 copies of the mutation at the major locus (aa) or 2 copies of the mutation at minor locus D (dd). Italian Greyhounds are 9 times more likely if they have 1 copy of the mutation at the major locus and at least 1 copy of mutations at minor loci b and c (Aa/ b-/c- genotype). Italian Greyhounds are 5 times more likely to develop PRA if they have 1 copy of the mutation at the major locus and at least 1 copy of mutations at minor loci d and e (Aa/ d-/e- genotype). Matings between dogs with AA genotype (and without “d” variant) will yield low risk offspring. Breeders should avoid mating any dogs that will produce puppies with PRA-susceptible genotypes.
Testing to identify Italian Greyhounds at higher risk of PRA-IG1 assists breeders to select mating pairs that avoid producing puppies with higher risk to develop this form of PRA. This test can be used to confirm the diagnosis of this form of PRA.
Note:This test is specific for 5 mutations associated with susceptibility to the major cause of PRA presently occurring in the Italian Greyhound breed. This test is not valid for other breeds. It is important to note that there may be other genetic form(s) of PRA in the breed. Further research is needed to identify additional causative mutations in Italian Greyhounds diagnosed with PRA in the absence of a PRA-IG1 genotype.