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Dominant Progressive Retinal Atrophy (D-PRA)
| Acronym: | D-PRA, AD-PRA |
| Gene: | RHO |
| Mutation: | c.11C>G |
| Inheritance: | Autosomal dominant |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Dominant Progressive Retinal Atrophy (D-PRA) is an eye disorder, which belongs to the progressive retinal atrophy group of disorders, known as PRA. This group of disorders comprises inherited diseases that lead to degeneration of retinal photoreceptor cells in dogs and other pets. In general, these diseases are characterized by poor dark vision, visual field defects, and abnormalities in the electroretinogram. PRA is progressive and easily leads to blindness and it appears in both eyes simultaneously. The age of onset and rate of retinal degeneration varies between the different forms of the conditions. Some forms of PRA are common to multiple dog breeds, while others are recognized in just a single breed. The retina is a thin tissue localized in the eye that contains photoreceptors, rods, and cones. Rods are important for vision in dim light, or also night vision. Rods contain a visual pigment called rhodopsin, which functions also as a receptor. Rhodopsin is activated by light and a transduction cascade that enables night vision initiated. PRA causes progressive rode degeneration, causing firstly night blindness and with time full blindness. In dominant PRA, numerous rhodopsin gene mutations have been identified. The appearance of first symptoms varies, depending on whether is the dog homozygous or heterozygous. Dogs homozygous for D-PRA mutation develop symptoms already at 3 months of age, while heterozygous start to show the same symptoms by 13 months of age when ERG results show abnormal rode and cone photoresponses. Usually, by 1 or 2 years of age, affected dogs develop complete blindness. There have been also cases reported where D-PRA affected dogs did not show any symptoms until the age of 7.
Dominant Progressive Retinal Atrophy (D-PRA) is caused by point mutation p.Thr4Arg in the RHO gene. It is inherited as an autosomal dominant disorder. This means that one copy of the mutated gene is enough for a dog to develop the symptoms of PRA. There has not been developed a cure for PRA. Since in some dogs symptoms of D-PRA do not occur until a few years of age (in some cases up to 7 years of age), it is important to be able to recognize a dog possessing the defected gene prior to breeding. The only way to detect mutated genes is to do genetic testing.
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. |
AFFECTED HETEROZYGOTE |
Tested mutation was detected in animal with „affected heterozygote“ result. Animal tested as affected heterozygote has one wild-type and one mutation allele, it is in heterozygous state. It is likely to 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.
**Penetrance of tested mutation, and potential unknown mutations or multiple other factors can possibly affect the likelihood of experiencing a genetic disorder.
References:
Kijas JW, et al (2002.): Naturally occurring rhodopsin mutation in the dog causes retinal dysfunction and degeneration mimicking human dominant retinitis pigmentosa .Proc Natl Acad Sci U S A. 2002 Apr 30;99(9):6328-33.