Genetic basis of Coat length in cats (short or long hair) - is primarily controlled by the Fibroblast Growth Factor 5 (FGF5) gene. This gene regulates the hair growth cycle by signaling when hair growth should stop. Short hair cats carry the dominant wild-type variant of the FGF5 gene, which functions normally to end the hair growth phase, resulting in shorter fur. Long hair cats have recessive mutations in the FGF5 gene. These mutations cause a loss of function, allowing the hair to continue growing longer before shedding. Cats must inherit two copies of these recessive mutations (either two identical or two different long-hair mutations) to have long hair. Carriers with only one copy will have short hair. At least four different recessive mutations (M1 to M4) in FGF5 are identified in cats, with some breed specificity: M1 is seen in Ragdoll and Siberian cats. M2 in Norwegian Forest, Siberian, Tiffanie, and related breeds. M3 in Ragdoll, Maine Coon, and Devon Rex. M4 is widespread across many long-haired breeds.
Pathophysiology - The FGF5 gene product is a protein that signals hair follicles to transition from the growth phase (anagen) to the resting phase (catagen). In short-haired cats, this signal occurs normally, thus limiting hair length. In cats with long-hair mutations, the defective or inactive FGF5 protein delays or prevents this signal, extending the hair growth phase. This leads to longer and denser coat development. Since hair continues growing longer before shedding, the fur appears long and luxurious. Long-haired cats require more grooming because their longer fur is prone to matting and tangling.
Complications - There are no direct health complications from the long or short hair itself, as coat length is a cosmetic trait. However, for long-haired cats: More grooming is needed to prevent matting and skin infections. Potential for overheating in warm climates due to thicker coats. Difficulty with shedding and furball formation requiring care. Short-haired cats generally have lower grooming requirements but may shed more visibly.
Why This Matters to Breeders and Vets - Breeding Decisions: Knowledge of the FGF5 gene and its variants allows breeders to predict coat length outcomes and select for desired traits while maintaining genetic diversity. Carrier Identification: Genetic testing can identify carrier cats who appear short-haired but can pass a long-hair gene to offspring. Breed Standards: Many breeds have specific standards or preferences regarding coat length; genetic testing supports breed compliance. Veterinary Care: Vets can advise on grooming needs and potential coat-related health issues based on coat type. Mutations and Diversity: Understanding multiple mutations responsible for long hair helps in designing comprehensive genetic tests for different breeds.
Summary - Cat coat length, short versus long hair is mainly determined by the FGF5 gene. Short hair is dominant, caused by normal FGF5 function, while long hair results from inheriting two recessive mutations in FGF5 that prolong hair growth. Four known mutations account for long hair in different breeds. Although the trait itself is non-pathogenic, long-haired cats require more grooming and care to prevent coat-related problems.
