Hairlessness in Terriers

Hairlessness in the dog has evolved independently at least twice. One form of hairlessness present in several breeds (Peruvian Inca Orchid, Chinese Crested, Mexican Xoloitzcuintle) is inherited as a dominant trait and is lethal in the homozygous state (two copies of the mutation). A second, recessive form defines the American Hairless Terrier, a breed thought to be derived through selective breeding from the Rat Terrier. Contrary to the dominant form, there are no adverse effects on dentition or fecundity associated with the recessive Terrier hairlessness.

The recessive Terrier hairlessness trait is caused by a frameshift deletion in the serum/glucocorticoid regulated kinase family member 3 gene (SGK3). A 4 bp deletion (TTAG) in exon 4 of SGK3 disrupts the protein coding sequence and is predicted to knock out the function of the gene. SGK3 has been shown to affect postnatal hair follicle development in mice and appears to have a similar function in dogs: American Hairless Terriers are born with a thin coat of hair that is lost within the first months of life.

Although the trait breeds true in the American Hairless Terrier, outcrosses are performed to systematically introduce variation and create a healthier, more diverse gene pool. These crosses benefit from DNA test results, which will assist breeders in identifying the coated dogs that carry the hairless mutation.

This DNA test for the recessive Terrier hairless trait distinguishes dogs with respect to the mutation: coated and clear (no mutant copy), coated and carrier (one mutant copy), or hairless (two mutant copies).

If a carrier dog (with a single copy of the hairless gene) is used in a mating, an offspring from the cross has a 50% chance of inheriting the mutation from this parent. If two carriers are mated, 25% of the offspring in the litter are expected to be hairless and another 50% of the puppies are expected to be carriers of hairlessness. Mating two clear dogs (C/C) will only produce clear puppies, which need not be tested by DNA.