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PRA-RCD2 (Progressive Retinal Atrophy)
| Acronym: | PRA-RCD2 |
| Gene: | RD3 |
| Mutation: | 22 bp insertion |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Progressive retinal atrophy (PRA) comprises autosomal recessively inherited diseases that lead to degeneration of retinal photoreceptor cells in dogs and other pets. In general, these diseases are characterized by disturbance of vision in the dark, visual field defects, and abnormalities in the electroretinogram, which can progress to blindness. Some forms of PRA are common to multiple dog breeds, while others are recognized in just a single breed. Rod-cone dysplasias are a group of recessively inherited diseases with early onset where photoreceptors are disturbed in their normal development and never manage to develop properly. The progression of rod-cone dystrophy is caused by sequential degeneration of rod and cone photoreceptors.
PRA-RCD2 is an autosomal recessive disorder that segregates in collie dogs. As far as is known, PRA-RCD2 segregates exclusively in rough and smooth collies. Night blindness is the earliest clinical sign detectable in 6-week-old affected dogs. Retinal dysfunction can be detected by electroretinography (ERG) as early as 16 days of age. At 6 weeks of age, when the photoreceptors of normal dogs are fully developed, only a few underdeveloped segments are visible in PRA-RCD2 dogs, by 2–2.5 months of age, they completely disappear in the affected retina. Both types of photoreceptors subsequently degenerate, cones more slowly than rods. Ophthalmoscopic abnormalities can be detected at 3.5 to 4 months of age, including tapetal hyperreflectivity, retinal vascular attenuation, and optic nerve pallor. By 6 to 8 months of age rcd2 dogs become functionally blind.
Results Reported As
Test Result |
Interpretation of test result |
CLEAR |
Tested mutation was not detected in animal with „clear“ result. Animal tested as clear has wild-type allele in homozygous state (i.e. two pairs of healthy alleles). It will not develop disease caused by tested mutation.* It will pass only wild-type allele to its offspring. |
CARRIER |
Tested mutation was detected in animal with „carrier“ result. Animal tested as carrier has one wild-type and one mutation allele, it is in heterozygous state. It will not develop disease caused by tested mutation.* It can pass wild-type or mutation allele to its offspring. |
AFFECTED |
Tested mutation was detected in animal with „affected“ result. Animal tested as affected has two copies of mutation alleles affecting the gene. It is likely the animal will experience a genetic disorder due to this mutation.** It will pass only mutation allele to its offspring. |
*Test excludes only tested mutation but not possible unknown mutations or factors that can lead to similar condition/symptoms.
** Potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Dekomien, G., Runte, M., Gödde, R., and Epplen, J.T. (2000). Generalized progressive retinal atrophy of Sloughi dogs is due to an 8-bp insertion in exon 21 of the PDE6B gene. Cytogenet. Cell Genet. 90, 261–267.
Kukekova, A.V., Goldstein, O., Johnson, J.L., Richardson, M.A., Pearce-Kelling, S.E., Swaroop, A., Friedman, J.S., Aguirre, G.D., and Acland, G.M. (2009). Canine RD3 mutation establishes rod-cone dysplasia type 2 (rcd2) as ortholog of human and murine rd3. Mammalian Genome 20, 109–123.