Hereditary variant of coat texture that defines the Selkirk Rex and manifests as a uniform curl of the coat, the whiskers and even the hair of the paw pads. It is a spontaneous mutation of the KRT71 gene, which encodes a type II keratin of the hair follicle. It does not involve systemic disease: it is an aesthetic trait with simple inheritance. Heterozygous individuals show a moderate, stable curl, while homozygotes show a very tight curl and a more fragile coat.

Trait specific to the Selkirk Rex breed, founded from a single animal in 1987. There are no published population frequencies outside the breed. The variant has not been described in other domestic cat breeds.

- Curly coat visible from birth
- Curled and often fragile whiskers
- More pronounced curl on the neck, tail, belly and legs
- Homozygotes: very tight curl and more fragile coat
- Heterozygotes: moderate curl, denser and more durable coat

The trait appeared in 1987 in Montana (United States) in a rescued cat with a curly coat named «Miss DePesto», mated to a Persian male by the breeder Jeri Newman. The breeding programme gave rise to the Selkirk Rex breed, recognised by the main feline associations in the following decades. The molecular basis was resolved in the 2010s when a splice variant of the KRT71 gene was identified, allelic with other variants of the same gene responsible for the curly or hairless coat of other feline breeds (Sphynx, Devon Rex). The dominance of the trait facilitated its rapid fixation in the breed.

- Mate curly × straight (heterozygote × non-carrier) to maintain heterozygosity and avoid hair loss in the homozygote
- Avoid curly × curly if a dense, durable coat is sought: homozygosity produces a more fragile coat
- Straight-coated animals born in a Selkirk Rex litter are not carriers and do not transmit the trait
- Genotype before matings with breeds outside the standard so as not to introduce the variant inadvertently

Distinguish genetically from the Devon Rex curl and the hairless coat of the Sphynx: although all affect KRT71, they are distinct alleles and compounds may show problematic intermediate phenotypes. Coat status varies with age and season; it should not be interpreted as a sign of disease. Hair fragility in homozygotes can be confused with scaling dermatopathies.

1. Gandolfi B, Alhaddad H, Joslin SE, Khan R, Filler S, Brem G, Lyons LA. A splice variant in KRT71 is associated with curly coat phenotype of Selkirk Rex cats. Sci Rep 3:2000, 2013. PMID: 23770706
2. Filler S, Alhaddad H, Gandolfi B, Kurushima JD, et al. Selkirk Rex: morphological and genetic characterization of a new cat breed. J Hered 103(5):727-733, 2012. PMID: 22837475
3. Gandolfi B et al. The naked truth: Sphynx and Devon Rex cat breed mutations in KRT71. Mamm Genome 21(9-10):509-515, 2010. PMID: 20953787 (contexto de alelismo)
4. Lyons LA. DNA mutations of the cat: the good, the bad and the ugly. J Feline Med Surg 17(3):203-219, 2015. PMID: 25701860
5. OMIA:001712-9685. Curly coat, Selkirk rex in Felis catus. https://omia.org/OMIA001712/9685/