There are also a number of rarer, less well known or developing rex coated breeds, including the German Rex, Ural Rex , Tennessee Rex , Tasman Rex Group and Skookum. Unrecognised rexed varieties have also been observed in breeds such as the Maine Coon and Persian, however there has been no significant attempt to develop or seek recognition for these varieties.
Though the breeds look similar and are sometimes grouped together for show purposes, each results from a separate mutation rather than being bred from a common ancestor. Each mutation causes the hair follicles to be oval in shape, instead of the normal regular round form, which results in hairs curling round as they grow instead of growing straight.
The name Rex was taken from the Rabbit Fancy because the first rex breed to be developed, the Cornish Rex, has a coat similar to that of a rex rabbit, in that it comprises only the undercoat with no topcoat or guard hairs.