Greying
Greying*
General description
Important: this test is only possible with 30 mane/tail hairs plucked out with the hair root (no EDTA blood!). Horses with this mutation are born coloured but gradually lose their hair pigmentation (not skin pigmentation) until they are grey or white at an age of about 6–8 years.
Order details
| Test number | 8159 |
| Sample material | mane/tail hair roots |
| Test duration | 21-28 working days |
Test specifications
| Inheritance | Allelic series: G dominant over N |
| Literature | OMIA:001356-9796 |
Detailed description
Important: this test is only possible with 30 mane/tail hairs plucked out with the hair root (no EDTA blood!)
Horses carrying the greying variant are born coloured and gradually lose pigmentation in their hair. The first signs of greying usually appear on the head, especially around the eyes. The skin pigmentation remains in its original colour. By the age of 6–12 years, the horses become completely grey/white.
The genetic cause is a variant in the STX17 gene. There are three alleles:
- N = normal, i.e. non-grey
- G2 = greying gene duplication – two tandem copies of the duplicated sequence cause grey/white coat colour
- G3 = greying gene triplication – three tandem copies of the sequence also cause grey/white, but these horses turn grey much faster and are often completely white at a young age
Greying is inherited in an autosomal-dominant manner, meaning that a single copy of either the G2 or G3 allele is sufficient to cause greying in a horse.
The development of skin cancer (melanoma) is directly associated with the greying variant: 70–80% of grey horses over 15 years of age have one or more melanomas. Horses with the G3 variant turn grey faster and have a higher risk of melanomas than those with G2. The likelihood (incidence) is also statistically influenced by the horse’s base coat colour, which is determined at another DNA locus, the Agouti locus. Grey horses that were born black have a significantly higher risk of developing melanomas than grey horses born with brown coat. It has also been reported that grey horses have a higher risk of developing squamous cell carcinomas of the eyes than other horses.
A 2024 study led by Dr Leif Andersson and colleagues at Uppsala University, in collaboration with researchers from the UC Davis Veterinary Genetics Laboratory (VGL), showed that the speed of greying and the risk of melanoma are influenced by the number of copies of this sequence responsible for greying in horses. It was shown that horses without a duplication (N/N) do not turn grey and have the lowest melanoma incidence. Horses with one G3 copy (N/G3) turned grey faster and developed melanomas more frequently, while horses homozygous for G3 (G3/G3) greyed the fastest and had the highest melanoma incidence. Horses with the G2 allele, whether heterozygous (N/G2) or homozygous (G2/G2), showed a low melanoma incidence similar to horses without duplications (N/N).
