The coat of the normal cat consists of three hair types: long and straight guard hairs of uniform diameter, thinner fawn hairs, and fine undulating down hairs of uniform thickness. A variety of rexoid and hairless breeds are documented to have alterations in their hair types. The autosomal recessive Rex coat (Devon curl) is generally missing the guard hairs and has reduced length and thickness in the undercoat hairs. Hairless in Sphynx cats is allelic to Devon and some Sphynx have tuffs of hair on the chest, ears, or tail. Causative mutations for two mutant alleles are actually allelic mutations in KRT71. The Sphynx mutation leads to a complete loss-of-function allele where the structure of the hair is seriously compromised, i.e., the hair is produced but is easily dislodged because of the lack of a well-formed bulb. In the Devon Rex, the mutation causes a remarkable alteration in the protein as well, but evidently residual activity of the protein still exists and results in curly body hair.
Gandolfi, B., Outerbridge, C.A., Beresford, L.G., Myers, J.A., Pimentel, M., Alhaddad, H., Grahn, J.C., Grahn, R.A., and Lyons, L.A. (2010). The naked truth: Sphynx and Devon Rex cat breed mutations in KRT71. Mamm. Genome 21, 509–515.