Genetic basis of the R locus in cats - controls the coat texture phenotypes including the curly coats of Devon Rex and Selkirk Rex breeds, as well as the hairless coat of Sphynx cats. This locus corresponds to the KRT71 gene, which encodes keratin 71, a structural protein critical for hair follicle formation and hair shaft integrity. Selkirk Rex curly coat (hr allele) is caused by a dominant mutation in KRT71. Cats heterozygous for this mutation have a wavy coat, while homozygotes exhibit a tighter and curlier coat texture along with a more slender body and larger ears. Devon Rex curly coat (re allele) results from a recessive mutation in KRT71, distinct from the Selkirk mutation. Cats need two copies of the re allele to express the Devon Rex curly short coat characterized by soft, fine curls and lack of guard hairs. Sphynx hairless coat (hr allele) is due to a different recessive mutation also in KRT71, leading to very sparse, fragile hair that gives the naked appearance. This mutation is allelic (at the same gene) but genetically distinct from the Devon Rex mutation. These three alleles at the R locus form an allelic series: KRT71SADRE (Selkirk Rex) > KRT71+ (normal) > KRT71re (Devon Rex) > KRT71hr (Sphynx hairless). Cats inherit these alleles in a codominant/recessive manner depending on the specific allele, influencing whether the coat is normal, curly, or hairless.
Pathophysiology - Mutations in KRT71 affect keratin filament formation and hair shaft structure: The Selkirk Rex mutation alters the keratin protein so that hair shafts have tightly curled, woolly texture. The Devon Rex mutation disrupts normal splicing and produces a truncated or abnormal keratin 71 protein, causing shortened, fragile, curly hair due to absent or defective guard hairs. The Sphynx mutation causes loss of functional keratin 71, leading to thin, broken hairs or near-total hairlessness. Because keratin 71 is crucial for hair follicle inner root sheath structure, these mutations manifest as altered hair growth and coat texture.
Complications - There are no significant health complications caused by the curly or hairless coat mutations themselves besides increased skin exposure in hairless cats leading to potential sensitivity to cold or sunburn. Breeders and owners should manage skin care carefully for hairless Sphynx cats, which lack the protective fur coat.
Why This Matters to Breeders and Vets - Breeders use genetic testing for KRT71 mutations to plan breeding pairs for desired coat types and avoid unexpected coat phenotypes. Understanding the inheritance (dominant for Selkirk Rex, recessive for Devon Rex and Sphynx) helps breeders maintain breed standards and predict offspring coat texture reliably. Veterinarians should be aware of these mutations to advise owners on care for hairless or curly-coated cats, particularly regarding skin protection in hairless breeds. These coat types are breed-defining and influence animal husbandry and welfare.
Summary - The R locus in cats corresponds to the KRT71 gene, controlling coat texture variants: Selkirk Rex curly coat results from a dominant KRT71 mutation producing wavy to curly hair and unique body traits. Devon Rex curly coat arises from a recessive KRT71 mutation causing soft, short curly hair lacking guard hairs. Sphynx hairless coat is due to another recessive KRT71 mutation resulting in near-complete hairlessness and fragile hairs. These alleles form an allelic series influencing coat phenotype. Genetic testing enables breeders to select for or against these traits intentionally. None of these mutations cause severe health issues, though hairless cats require special care.
