Grey causes accelerated loss of pigment in the coat which will slowly turn white as the horse ages
Breeds known to carry this mutation
Grey causes accelerated loss of pigment in the hair. The foal is born a solid colour, then white hairs will become mixed in with coloured hairs around the body. Eventually the horse becomes all white. Rate of greying can vary significantly.
Grey is also associated with the development of melanomas, with homozygous horses more likely to develop them than heterozygotes. The melanomas are not cancerous; however, they can become large, obstructive and uncomfortable and may need to be removed.
Interpretation of results
n/n: Horse does not carry the mutation that causes greying with age.
G/n: Horse carries one copy of the mutation that causes greying with age and will turn white over time.
G/G: Horse carries two copies of the mutation that causes greying with age, will turn white with time and is more susceptible to developing melanoma. It will also pass on the grey variant to all of its offspring.
Pielberg et al. A cis-acting regulatory mutation causes premature hair graying and susceptibility to melanoma in the horse. Nature Genetics 2008; 40:1004-9. doi: 10.1038/ng.185