HAIRLESS GENE
It has recently been the main topic of discussion among hairless dog breeders around the world that some Judges are perceived to have little understanding about the DNA behind the Hairless breeds - that which makes them unique in the dog world.
Recent scientific studies have discovered many new things about the genetics of hairless dogs that determines where and how much hair they have and the number of teeth. The Foxi3 gene has been identified as the one that controls the placement of hair and the number, shape and retention of teeth.
... It has been commented on by many experienced breeders across the world that judges are expecting Hairless dogs to have full dentition and not to have missing teeth. This is a misconception and shows a lack of understanding of the finer points of the hairless breeds.
Hair and teeth have been found to be controlled by the same gene which has been modified over millions of years. When one gene is modified, as has occurred with the Foxi3 gene in Hairless dogs, then it can be expected that all features controlled by that gene will be altered. Hairless dogs are hairless due to the modification of the Foxi3 gene. The dentition of Hairless dogs is also affected by the Foxi3 gene, therefore missing teeth and a different shape of tooth are to be expected.
It should always be remembered that the Hairless variety is NOT to be penalized for missing or irregular shaped teeth (as per the ANKC extended breed standard). The phenotype of the Hairless dogs is classified as Canine Ectodermal Dysplasia (CED.) The Foxi3 gene is the regulator of Ectodermal development which includes teeth. Due to this modification of the hair there MUST be an exception of a modification of the teeth
It has also been brought to the attention of breeders of Hairless dogs that some Lecturers, during judges training lectures, are giving their own opinions that Hairless dog breeders should have "fixed" the problem of lack of dentition by now. From the above information, it can be surmised that, due to genetics, it is not possible to have full dentition and hairless bodies.
Telling Hairless dog exhibitors that the dog is being dismissing because it has missing teeth is the same as dismissing a Rhodesian Ridgeback exhibitor because you do not like the backwards ridge on their dog's spine.
It is simple genetics, we cannot, no matter how hard we try, alter the genetics behind our dogs' lack of hair and teeth. The simple way to understand this is to look at other hairless animals such as Elephants, Pigs, and Hippos they all have some modification of body hair and teeth. Hairless dogs have specialized characteristics, please judge them accordingly.
The Hairless allele (the wild type) is a dominant (and homozygous prenatal lethal) trait, while the Powder puff allele acts as a simple recessive trait in its presence. Zygotes that receive two copies of the Hairless allele will never develop into puppies. Thus all Chinese crested carry at least one copy of the Powder puff allele.
The crested is not affected by many of the congenital diseases found in “toy breeds”. They are, however, prone to some of the conditions below. Crested have what is called a “primitive mouth”. This means that most of their teeth are pointy like their canines. Hairless varieties of the Crested can be prone to poor dentition. Poor dentition may include missing or crowded teeth and teeth prone to decay when not properly cared for. Most dogs of the Puff variety have few, if any, dental defects. Eyes are a concern within the breed, having at least two forms of “progressive retinal atrophy” (PRA) which can eventually lead to blindness. For one of these forms of PRA, there exists a genetic test, “prcd-PRA”. Since this test can only reveal the existence of affected or carrier status of this one form of PRA, breeders and owners of the breed should still have regular eye exams by veterinary ophthalmologists. The breed also suffers from another eye disease called “Keratoconjunctivitis sicca” (KCS) or “dry eye syndrome” (DES).
Crested can develop canine multiple system degeneration (CMSD) also called “progressive neuronal abiotrophy“ (PNA) found in Kerry Blue Terriers. This is a progressive movement disorder that begins with “cerebellar ataxia” between 10 and 14 weeks of age. After 6 months of age, affected dogs develop difficulty initiating movements and fall frequently. The gene responsible has been mapped to canine chromosome 1.
As with all other toy breeds, the Crested can be prone to “patellar luxation”. This inheritable condition is caused by shallow knee joints (stifles) and results in kneecaps that pop out of place. Its onset is often at a young age, and can cause temporary to permanent lameness based on the severity. Breeders should have their stock certified free of “patellar luxation”.
“Allergy”, “Epilepsy” and “Autoimmune” diseases have been observed in the breed. The severity of these ailments, which can lead to the premature death of the dog, means this is something breeders need to take seriously in order to avoid it becoming a problem for the breed.
HAIRLESS STRUCTURE
Thank you Aga Mazurek - Artagasamazis Kennel in Poland for the use of your art pictures.
Progressive Retinal Atrophy
Progressive Rod-Cone Degeneration
(PRA-prcd)
Progressive Retinal Atrophy, Progressive Rod-Cone Degeneration (PRA-prcd) is inherited as an autosomal recessive disease. Degeneration of both rod and cone photoreceptor cells of the retina of PRA-prcd affected dogs usually occurs 3 to 5 years of age or later. Affected dogs initially experience night blindness and loss of peripheral vision. As the disease progresses, complete blindness will occur in time. Different breeds and individual dogs may experience variation in the age and rate of the disease progression.
DDC Veterinary is offering DNA Testing for PRA-prcd (PRCD c.5G>A). Breeders have an accurate, convenient, and affordable tool to help them avoid producing PRA-prcd affected offspring and significantly reduce the gene frequency in future generations.
This mutation affects several breeds like the Chesapeake Bay Retriever, Chihuahua, Cocker Spaniel, Golden Retriever, Labrador Retriever, Poodle and Yorkshire Terrier. To see if this test is available for your breed, use the Order Canine Tests by Breed tool to see a complete list of DNA tests.
There are 3 possible genotypes reported for Progressive Retinal Atrophy, Progressive Rod-Cone Degeneration:
CLEAR (those having 2 copies of the normal allele and appear to be normal)
CARRIER (those having 1 copy of the normal allele and 1 copy of the PRA-prcd mutation but appear to be normal)
AT RISK (those having 2 copies of the PRA-prcd mutation and will develop blindness over time)
It is important to note, although carriers will not show clinical signs of the disease, if used for breeding, they will likely pass on the mutation 50% of the time, therefore a carrier to carrier mating will likely result in producing affected pups in about 25% of the offspring.
Results are based upon the specific prcd c.5G>A mutation. There are multiple types of PRA caused by other gene mutations. Clear results for PRA-prcd only pertain to the prcd c.5G>A mutation tested. It will not detect if a dog has any other form of Progressive Retinal Atrophy.
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