Hairlessness in dogs

The absence of fur is a desired trait in several breeds. Today there are only a few hairless dog breeds that are recognized by major breed registries. Chinese Crested Dog, Peruvian Hairless Dog and Xoloitzcuintli lose their fur due to a different mutation (FOXI3) than the recently developed American Hairless Terrier (SGK3).

Hairlessness: Xolo-Type

This dominant type of hairlessness is found in the Chinese Crested Dog, Peruvian Hairless Dog, Xoloitzcuintli and related breeds. These are old breeds that probably share a common ancestor[1].

Hairlessness Dog Chinese Crested Dog puppy

Although the Chinese Crested Dog is believed to maybe have an Asian or African origin the breed we know today probably shares a common ancestor with the Mexican Chihuahua[6].

All of these hairless dogs show varying degrees of hairlessness but most often the entire body is affected. Depending on the breed there might be some tufts of hair on the legs, head or tail[3]. Compared to coated dogs they only have very simple primary hair follicles.

Hairlessness Dog Xolo

The Hr-Locus (Xolo-Type)

Xolo-type hairlessness is caused by a mutation in the FOXI3 gene (forkhead box transcription factor I3) on dog chromosome 17.

FOXI3 regulates the development of ectodermal appendages such as hair follicles, teeth, and different glands. This gene is important to embryonic development and is expressed in hair follicles or dental epithelium[4].

So, what happens in hairless dogs?

The mutation at the Hr-Locus responsible for the Xolo-type of hairlessness causes a loss of most of the normal protein. And the resulting FOXI3 deficiency interferes with the development of normal hair follicles.

Hairlessness Dog Peruvian Hairless Dog

Unfortunately, too little FOXI3 is also associated with defects in teeth, brittle toenails as well as malformations of the ear or sweat glands. Newborn hairless puppies may even have a smaller chance to survive compared to their normal littermates[1,3].

This type of hairlessness is categorized as Canine Ectodermal Dysplasia (CED).

Affected dogs not only have problems with post-natal hair growth and hair regeneration but also with dentition (missing teeth, abnormal teeth). At least, other defects seem to be less common[1,3].

Hairlessness Dog Xolo abnormal teeth

The mutant variant Hr at the Hr-Locus is an autosomal semi-dominant trait[4]. One copy of this mutation (Hr/hrc) is enough to cause a hairless phenotype while a homozygous dominant genotype (Hr/Hr) is embryonic lethal.

Dogs with two wild-type alleles (hrc/hrc) have a normal coat.

Hr > hrc

Since this is a dominant trait it will be expressed in every puppy that inherits one copy.

So Chinese Crested Dogs, Xolo or Peruvian Hairless Dogs have a 50 % chance to pass on their hairless variant to each puppy, even in mixed breed litters.

Ever wanted to know what a “Crested Frenchie” might look like? Here you go:

Hairlessness Dog Chinese Crested Dog Frenchie

FOXI3 Hairlessness Calculator

Hairless dogs with a mutation in the FOXI3 gene are always heterozygous (Hr/hrc). In any combination these dogs can always produce hairless or fully coated offspring in the same litter.

Breeding from two hairless dogs may result in a reduced litter size since each potential puppy has a 25 % chance to have an embryonic lethal Hr/Hr genotype.

Chinese Crested Dogs

Chinese Crested Dogs can be completely hairless or semi-coated with a hairless torso and silky tufts of hair on the head, legs and tail.

There are some intermediate forms with some hair mainly on the top of the head. There might be some unknown modifier genes that influence the expression of this trait.

The coated variety is known as Powder Puff. These dogs have normal compound hair follicles identical to those in coated dog breeds[5].

Chinese Crested Dogs are obviously longhaired. Interestingly, they are also bearded and can even be curly.

LongCurlyWireFOXI3

Peruvian Hairless Dog

The Peruvian Hairless Dog and the related Peruvian Inca Orchid have a hairless torso and can have some short hairs on the head, feet and tail.

Since this breed seems to be genetically shorthaired and non-bearded, they never grow the longer or wavy tufts of hair seen in crested dogs.

LongCurlyWireFOXI3

Mexican Hairless Dog

The Xoloitzcuintli or Mexican Hairless Dog most commonly has only short hair on head, feet and tail.

The coated variety has the typical phenotype of a primitive village dog with pricked ears and a short coat without facial hair or curls.

But during breed formation, different kinds of dogs were used to save this rare breed from extinction. Aside from semi-wild village dogs with a hairless phenotype, there might have been many outcross breedings to longhaired or even curly breeds.

So it’s not unheard of that some coated Xolos are born with a bearded, long or curly coat!

LongCurlyWireFOXI3

Hairlessness: Terrier-Type

Around 1972 a breeder began to breed a hairless variety of the Rat Terrier after a healthy but hairless puppy was born in one of her Rat Terrier litters.

Puppies are born with a tennis ball-like fuzz but lose all of their coat during the first few weeks after birth. This is classified as some kind of hypotrichosis or juvenile alopecia but it is not associated with any health issues or poor teeth quality.

This type of hairlessness seems to be caused by a relatively new mutation only found in the American Hairless Terrier (AHT). In 2016 the AHT was finally recognized as a distinct new breed by the American Kennel Club.

The hr-Locus (Terrier-type)

The hairlessness in American Hairless Terriers s caused by a mutation in the SGK3 gene (serum/glucocorticoid regulated kinase family member 3) on dog chromosome 29[1].

Interestingly, Scottish Deerhound can also produce hairless dogs from coated parents. Researchers discovered yet another recessive mutation in the SGK3 gene that causes juvenile early onset hair loss in this breed[2,7].

SGK3 seems to be important for the development or maintenance of hair follicles after birth. American Hairless Terriers are born with a little bit of coat but then lose it all permanently.

Hairlessness in the AHT is an autosomal recessive trait. Even one copy of the dominant wild-type Hrc produces a normal coat, a dog needs two copies to be hairless (hr/hr).

Hrc > hr

SGK3 Hairlessness Calculator

The hairlessness in the American Hairless Terrier is caused by a homozygous recessive genotype (hr/hr). Unlike the hairlessness in Xolos, this is not an embryonic lethal trait.

Coated dogs can carry this trait (Hrc/hr) and produce hairless offspring with other carriers or affected dogs. This sometimes happens in mixed breeds dogs when both parents have some American Hairless Terriers in their ancestry.

American Hairless Terrier

American Hairless Terriers are born with a very sparse and thin puppy coat that is commonly lost during the first few months of life. The dogs are otherwise healthy and don’t suffer any health issues associated with the dominant Xolo-type of hairlessness.

Hairlessness Dog American Hairless Terrier sit

So for, the American Hairless Terrier is the only dog breed with this version of recessive hairlessness[1].

The AHT emerged from the Rat Terrier which goes back to multi-terrier crosses and feists but also to Beagle, Miniature Pinscher or Italian Greyhound. If coated AHT are born, they are usually shorthaired.

LongCurlyWireSGK3

Hairless Dog Breeds

The American Hairless Terrier has a special status among the hairless breeds since these dogs have their very own type of hairlessness.

But most of the hairless dog breeds we know today seem to share a common ancestor.

The hairless dogs from South America like Xolo, Peruvian Hairless Dog and surprisingly the Chinese Crested Dog are considered to be old breeds descending from hairless dogs of the Aztecs and Incas. But the officially recognized versions of these hairless breeds were actually only developed rather recently.

There are a handful of related breeds that are very rare like the Cuban Hairless Dog, Argentine Pila Dog, the Bolivian Hairless Dog, the Ecuadorian Hairless Dog, and the Hairless Khala also from Argentina.

Others hairless dogs are the Jonangi from eastern coastal areas in India or the African Hairless Dogs that seem to be extinct but were known as Abyssinian Sand Terrier among other names.

Learn More

Links

[1] Parker, H. G., Harris, A., Dreger, D.L., Davis, B.W., & Ostrander, E.A. (2017). The Bald and the Beautiful: Hairlessness in Domestic Dog Breeds. Philosophical Transactions of the Royal Society B, 372(1713). https://doi.org/10.1098/rstb.2015.0488

[2] Heidi G Parker, D Thad Whitaker, Alexander C Harris, Elaine A Ostrander. Whole Genome Analysis of a Single Scottish Deerhound Dog Family Provides Independent Corroboration That a SGK3 Coding Variant Leads to HairlessnessG3 Genes|Genomes|Genetics, Volume 10, Issue 1, 1 January 2020, Pages 293–297. https://doi.org/10.1534/g3.119.400885

[3] Online Mendelian Inheritance in Animals (OMIA). Sydney School of Veterinary Science, University of Sydney. OMIA 000323-9615 (01/2016): Ectodermal dysplasia in Canis lupus familiaris. https://www.omia.org/OMIA000323/9615/

[4] Drögemüller C, Karlsson EK, Hytönen MK, Perloski M, Dolf G, Sainio K, Lohi H, Lindblad-Toh K, Leeb T. 2008. A mutation in hairless dogs implicates FOXI3 in ectodermal developmentScience321, 1462. https://doi.org/10.1126/science.1162525

[5] Wiener, D.J., Gurtner, C., Panakova, L., Mausberg, T.B., Müller, E.J., Drögemüller, C., Leeb, T., Welle, M.M. :
Clinical and histological characterization of hair coat and glandular tissue of Chinese crested dogs. Vet Dermatol 24:274-e62, 2013. https://doi.org/10.1111/vde.12008

[6] Parker, Heidi & Dreger, Dayna & Rimbault, Maud & Davis, Brian & Mullen, Alexandra & Carpintero-Ramirez, Gretchen & Ostrander, Elaine. (2017). Genomic Analyses Reveal the Influence of Geographic Origin, Migration, and Hybridization on Modern Dog Breed Development. Cell Reports. 19. 697-708. https://doi.org/10.1016/j.celrep.2017.03.079

[7] Hytönen, M.K., Lohi, H. A frameshift insertion in SGK3 leads to recessive hairlessness in Scottish Deerhounds: a candidate gene for human alopecia conditionsHum Genet 138, 535–539 (2019). https://doi.org/10.1007/s00439-019-02005-9