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Dog Hairlessness – Ectodermal Dysplasia (CED)
| Acronym: | CED |
| Gene: | FOXI3 |
| Mutation: | c.57_63dup |
| Inheritance: | Autosomal semi-dominant |
| Sample type: | CHS (Cheek Swab), WBE (Whole Blood EDTA) |
Genetics and characteristics
Dog hairlessness is an inherited trait caused by a genetic mutation in the DNA. Worldwide recognized hairless dog breeds are the Chinese crested dog, the Mexican hairless dog, and the Peruvian hairless dog. The Mexican hairless dog is also known as the Xoloitzcuintli, and it was considered sacred by the Aztecs. Hairless dogs’ phenotype is classified as canine ectodermal dysplasia (CED). Its characteristics are missing or abnormally shaped teeth in addition to a hair coat that is sparse or absent. CED is inherited in an autosomal dominant inheritance pattern and it is linked to chromosome 17 in Mexican hairless dogs, Peruvian hairless dogs, and Chinese crested dogs. All of those three dog breeds share the same mutation, and researchers say it probably appeared in Mexican hairless dogs 4,000 ago and was eventually passed on to the other two breeds due to a breeding program. As the research revealed, the mutation responsible for hairlessness in dogs is a seven base pairs insertion of genetic code into a gene known as FOXI3. This form of mutation is identified in all hairless dogs.
Since it is inherited as an autosomal dominant trait, heterozygous dogs’ phenotype appears as hairless and can vary in stages of hairlessness. Hair appears mostly only on a crest on the head, feet, and tail. Dogs that do not possess the mutated gene are referred to as powder puffs. The characteristic of the powder puffs is that their body is covered in a long, silky coat. Homozygous is lethal and when the dog contains one pair of mutated genes, it dies already during embryogenesis. A specific form of dog hairlessness is inherited as an autosomal recessive trait, which was identified only in the American Hairless Terriers. Homozygous in American Hairless Terriers is not lethal. Some health problems are associated with hairlessness, and those health problems are not necessarily genetic. They are mostly skin problems and allergies. Hairless dogs are more likely to get sunburn and skin cancer, due to a lack of natural protection from the sun. In dominant hairless dogs, tooth problems can occur (most common molars).
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:
Wiener, D., J. (2013): Clinical and histological characterization of hair coat and glandular tissue of Chinese crested dogs. Vet Dermatol 24, 274–e62
Drögemüller, C. (2008.): A Mutation in Hairless Dogs Implicates FOXI3 in Ectodermal Development. Science 2008 Sep 12;321(5895):1462.