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Progressive Retinal Atrophy Papillon & Phalène Type (PAP-PRA 1)
| Acronym: | PAP-PRA, CNGB1-PRA |
| Gene: | CNGB1 |
| Mutation: | c.2387_2389delinsCTAGCTAC |
| Inheritance: | Autosomal recessive |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Progressive retinal atrophy Papillon and Phalène type (PAP-PRA) is a form of PRA disorder. PRA stands for progressive retinal athrophy, a group of inherted eye disorders. Progressive retinal atrophy is characterized by progressive rod degeneration, followed by cone degeneration. PRA is a leading cause of blindness among dogs and shares similar symptoms to retinitis pigmentosa, an eye disease in humans that is also the leading cause of blindness among humans. There are many different forms of PRA and it has been identified in a number of dog breeds. Some forms of PRA are specific to a certain breed. PAP-PRA is such a form of PRA, specific for the Papillon breed. According to FCI, the Papillon breed is separated into two different breeds, Papillon and Phalène. Their segregation is based on morphological features. The American Kennel Club recognizes both breeds simply as Papillon. Based on the same origin, Papillon and Phalène share genetic causes of PRA. The most typical form of PRA causes primary rod degeneration. Rods are light-sensitive photoreceptors and their degeneration results in night blindness. PRA appears graduadly and is of progressive nature. It can progress from the beginning stage of night blindness until a severe form of PRA which includes complete blindness. The onset of clinical symptoms in affected Papillon and Phalène dogs is at 5 to 6 years of age. Examination of affected dogs with electroretinogram (ERG) reveals primary loss of the rod photoreceptor cells, which is afterward followed by cone cell degradation.
Progressive retinal atrophy Papillon and Phalène type (PAP-PRA) is caused by a frameshit mutation in the cyclic nucleotide gated channel beta 1 (CNGB1) gene. Research revealed a high percentage of the affected gene carriers. Among 145 tested Papillon and Phalene dogs, the occurrence of carriers was 17.2%. PAP-PRA is inherited in an autosomal recessive pattern. Healthy parents of an affected dog are obligate heterozygotes and therefore carry one mutant allele. Heterozygotes have no symptoms. At conception, each cub 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:
Ahonen SJ, Arumilli M, Lohi H (2013) A CNGB1 Frameshift Mutation in Papillon and Phale`ne Dogs with Progressive Retinal Atrophy. PLoS ONE 8(8): e72122. doi:10.1371/journal.pone.0072122