The amber colour of the Norwegian Forest Cat is a recessive coat phenotype described almost exclusively in this breed. Kittens are born with a dark coat (black or tabby) and progressively lighten towards amber or cinnamon tones during the first months; it is due to a loss-of-function allele of the MC1R gene (Extension locus) that prevents the production of eumelanin. It is not a disease.

Amber has been documented only in the Norwegian Forest Cat. No reliable carrier frequencies are available in large published series.

- No clinical signs: it is a coat phenotype, not a disease\n- Birth with a dark coat (black or tabby)\n- Progressive lightening towards amber/cinnamon during the first months\n- e/e homozygotes: amber phenotype\n- E/e carriers: dark coat, no signs\n- Allele practically exclusive to the Norwegian Forest Cat

Amber (formerly called 'X-Colour') was recognised in the Norwegian Forest Cat as a recessive colour absent in other breeds. Peterschmitt et al. (2009) sequenced MC1R in amber cats, carriers and controls, and associated the phenotype with the recessive e allele, defined by the variant c.250G>A p.(Asp84Asn); the allele was found only in amber cat lines.

- It is not a disease test: it serves to plan colour matings\n- Two E/e carriers can produce amber kittens (25 %), even if both parents are dark\n- An e/e cat with a carrier mate can also produce amber\n- Interpret together with the Orange locus (X-linked) and other coat loci\n- Do not select for colour over health or temperament criteria

Amber is an allele of MC1R (Extension locus), not an X-linked colour. It must be differentiated from the Orange gene (O, X-linked), the Agouti locus and other feline MC1R variants (Burmese russet, Kurilian Bobtail copal). The test detects the e allele, but not other coat loci. Amber kittens are born dark and lighten over time, so the neonatal phenotype does not predict the adult colour.

1. Peterschmitt M et al. 2009. Mutation in the melanocortin 1 receptor is associated with amber colour in the Norwegian Forest Cat. Anim Genet. PMID: 19422360
OMIA001199-9685.