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PRA-CORD2 – Progressive Retinal Atrophy
| Acronym: | PRA-CORD2, PRA-crd |
| Gene: | NPHP4 |
| Mutation: | c.479_526+130del |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
PRA-CORD2 is an inherited disorder that belongs to a group of eye disorders known as progressive retinal atrophy. Progressive retinal atrophy (PRA) includes autosomal recessively inherited diseases that lead to degeneration of retinal photoreceptor cells in dogs and other pets. It is a canine equivalent to retinitis pigmentosa (RP), an inherited eye disorder affecting human beings. The first case of PRA was observed in England more than a hundred years ago. In general, PRA is characterized by disturbance of vision in the dark, visual field defects, and abnormalities in the electroretinogram. It appears in both eyes simultaneously. The age of onset and rate of retinal degeneration varies between the different forms of the conditions. There are two types of photoreceptors in the eye, rods, and cones. Rods have an important role in vision in dim light and also night vision. PRA causes rode degeneration and in this way leads to night blindness. Researchers estimated that PRA causes the death of around 95% of the dog’s photoreceptors. Dog owners or breeders recognize PRA by ”glow” or ”increased shine” in the eyes. The disease is progressive. The initial stage is characterized by night blindness, while the advanced stage of PRA can cause full blindness in the dog. After the appearance of the first symptoms, it usually takes one year for the disorder to progress from the initial to the advanced stages, causing severe and irreverisble damage to the dog’s eye.
PRA-CORD2 is a specific form of PRA that belongs to a group known as cone-rode dystrophies (CORD). The cone-rode dystrophies affect humans and dogs. The characteristic of CORD is that cones are affected first and the rods second, which is the opposite in other forms of PRA. But nevertheless, dogs with PRA-CORD2 will lose their ability to vision with time and there is no cure currently available. The first symptoms usually occur between 10 months to 3 years of age. PRA-CORD2 is an inherited autosomal recessive disease. It is caused by a mutation in the NPHP4 (nephronophthisis 4) gene. Based on research, it is estimated that around 9.5% of the Wire-haired dachshund population possesses the defected gene responsible for this disorder. Carriers of the gene are heterozygous and do not develop the disease’s symptoms. When mating two carrier dogs, each puppy has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier.
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:
Mellersh, C., S. (2006.): Canine RPGRIP1 mutation establishes cone–rod dystrophy in miniature longhaired dachshunds as a homologue of human Leber congenital amaurosis. Genomics 88, 293-301.
Wiik, A., C., (2008.): A deletion in nephronophthisis 4 (NPHP4) is associated with recessive cone-rod dystrophy in standard wire-haired dachshund. Genome Res. 18: 1415-1421.