Russet is a coat pattern described in the Burmese in which kittens are born with a normal brown (sable) appearance and progressively develop a reddish-coppery tone over the following weeks and months. It is not a disease but a cosmetic colour trait. It can be confused with chocolate/champagne or with decolorations of other origin if the coat's evolution is not known.

Trait exclusive to the Burmese and derived breeds that share those lineages. The variant is uncommon and concentrated in specific lines; there are no reliable published frequencies: limited data.

- Kittens born with an apparently normal brown colour\n- Progressive reddish or amber tone of the coat from the kitten stage\n- Intensification of the colour with age\n- No associated disease signs

The phenotype caught the attention of Burmese breeders because the colour changes with age, contrary to what would be expected in a stable coat. It was characterised as a hereditary trait specific to the breed and was later incorporated into feline colour panels. Molecular characterisation was completed in 2017 with the identification of the three-base-pair deletion in MC1R (allele e^r), which makes it possible to distinguish russet from the other alleles of the extension locus.

- Cosmetic trait: the breeding decision depends on the cattery's aesthetic goals.\n- Do not mate two carriers if russet is not wanted in the offspring (average 25% homozygotes).\n- A carrier can be mated to a clear cat without producing russet kittens.\n- Also record the classic colour genotypes (agouti, dilution, chocolate, albino point cb) to plan the cattery's palette.

Do not confuse russet with chocolate/champagne (B locus) or with the thermal lightening of the point pattern; the colour change with age guides the diagnosis. It should also be differentiated from decolorations due to diet, sun or disease in growing kittens. When in doubt between phenotype and genotype, the colour test provides confirmation.

1. Gustafson NA, Gandolfi B, Lyons LA. Not another type of potato: MC1R and the russet coloration of Burmese cats. Anim Genet 48(1):116-120, 2017. PMID: 27671997
2. 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
3. Peterschmitt M, Grain F, Arnaud B, Deléage G, et al. Mutation in the melanocortin 1 receptor is associated with amber colour in the Norwegian Forest Cat. Anim Genet 40(4):547-552, 2009. PMID: 19422360 (contexto del locus E)
4. OMIA:001199-9685. Coat colour, extension in Felis catus. https://omia.org/OMIA001199/9685/