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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.
Alleles:
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.
Results of this test can be submitted to the OFA (Orthopedic Foundation for Animals)
Italian Greyhound Health Panel
$105 per animal
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
|
Locus |
A |
B |
C |
D |
E |
|---|---|---|---|---|---|
|
PRA-risk allele |
12% |
30% |
19% |
9% |
25% |
|
Normal allele |
88% |
70% |
81% |
91% |
75% |
|
Total dogs tested |
300 |
299 |
300 |
146 |
142 |
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.