Hairlessness in dogs

Mutation 7-bp duplication within exon 1 of FOXI3 gene causes canine ectodermal dysplasia, that is characterized by hairlessness and missing or abnormally shaped teeth. This mutation was found in  Chinese Crested, Peruvian Inca Orchid (Peruvian Hairless) and Mexican Xoloitzcuintle breeds.

Affected dogs have varying degrees of hairlessness but most commonly, almost the entire body is affected. Depending on the breed, there will be tufts of hair on the distal limbs and the top of the head. Some dogs have very abnormal teeth, many of which are missing. Others appear to have only mild abnormalities. Toenails may be long and brittle.

The hairless trait is dominantly inherited. It means that the hairless trait appears in dogs carrying only one mutant allele (a dog only needs to inherit one copy of the gene, either from the mother or the father). Dogs carrying 2 mutations (a dog inherits the mutation from both parents) in the gene FOXI3 die in prenatal stage and therefore only 2 variants are born:

Hairless dog - carries one copy of the mutation in the gene FOXI3

• the dog has a clean, smooth body with no hair except a crest on the head, feet (socks) and tail.
• more frequent incidence of mild to severe abnormalities of teeth (wrongly developed teeth, the teeth are not strong enough, dogs of higher age loose the teeth)
• neonatal deaths are more common in hairless pups than among their normal littermates (powderpuff)

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Powderpuff - is not a carrier of the mutation in gene FOXI3

• the whole body is covered with fine long silky coat

In spite of the clearly described phenotype difference between the two gene varieties, it is sometimes difficult to differentiate these phenotypes. For example, at first glance there is hardly any difference between the clean shaven Powder Puff and the true hairless dog. The genetic test helps to distinguish between these two varieties.

The hairlessness inheritance:

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References:
Drögemüller C, et al.: A mutation in hairless dogs implicates FOXI3 in ectodermal development; Science. 2008 Sep 12;321(5895):1462.