Hr Locus (FOXI3 Hairless Gene Test, Mexican Hairless, Peruvian Hairless and Chinese Crested Type)

Other Names: Ectodermal Dysplasia, ED
Affected Genes: FOXI3
Inheritance: Autosomal Dominant
Mutation: chr17:38032489-38032490 (canFam3): 7 bp duplication (dup GCCCGCC)
Breed(s): Chinese Crested, Mexican Hairless Dog, Peruvian Hairless Dog
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Testing Summary

The Hr Locus (Hairless) trait test reliably determines if a dog has one of the following genotypes at the Hr locus:


This dog carries two copies of the dominant Hr Allele which is lethal causing pups to die In Utero.

Interpretation: Embryonic lethal


This dog carries one copy of the dominant Hr allele and one copy of the recessive hr allele which produces hairlessness. This dog will pass on the Hr allele to 50% of its offspring and the hr allele to 50% of its offspring.

Interpretation: Hairless


This dog carries two copies of the recessive hr allele which results in a coated dog. This dog will pass on the hr allele to 100% of its offspring.

Interpretation: Coated, Powderpuff

Detailed Summary

The Hr Locus (Hairless) impacts the presence or absence of a coat on certain breeds of dog. A DNA variant in the FOXI3 gene, an important gene during early embryonic development, disrupts the normal development of hair and teeth in the dog which can result in sparse or absent hair as well as missing or abnormally shaped teeth. The hairless variant is inherited in an Autosomal Dominant fashion meaning only one copy of the FOXI3 gene variant is required to produce hairlessness. However, inheriting two copies of Hr is not compatible with life causing pups to die In Utero. Therefore, breeding two hairless dogs (hr/Hr) may result in reduced litter sizes.

Testing Tips

Genetic testing of the FOXI3 gene will reliably determine whether or not a dog is a genetic Carrier of the variant that produces a sparse or absent hair and missing or abnormally shaped teeth. Breeding two hairless dogs will result in slightly reduced liter-sizes because about 25% of the puppies will inherit two copies of the Hr Allele and will die In Utero. However, about two-thirds of the surviving litter will have one copy of the hairless variant (hr/Hr) and have sparse or absent hair and one-third of the liter will have two copies of the haired variant (hr/hr) and be coated dogs. Note: In our laboratory, we have identified hairy hairless Chinese Crested dogs as either carriers or clear for this Mutation. This indicates that the genetics of hairy hairless Chinese Crested dogs is not completely understood and there are likely other modifiers in the genome that interact with this gene.

There may be other causes of this condition in dogs and a normal result does not exclude a different mutation in this gene or any other gene that may result in a similar genetic disease or trait.


  • Drgemller C, Karlsson EK, Hytnen MK, Perloski M, Dolf G, Sainio K, Lohi H, Lindblad-Toh K, Leeb T. A mutation in hairless dogs implicates FOXI3 in ectodermal dysplasia. Science 2008 Sep; 321:1462. [PubMed: 18787161]
  • Shirokova V, Jussila M, Hytnen MK, Perl N, Drgemller C, Leeb T, Lohi H, Sainio K, Thesleff I, Mikkola ML. Expression of Foxi3 is regulated by ectodysplasin in skin appendage placodes. Dev Dyn 2013 Jun; 242:593-603. [PubMed: 23441037]