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Equine colour: Roan zygosity

Color & coat · Horse

Zygosity test for the roan pattern, which analyses the KIT haplotypes associated with the scattered mottling of white hair mixed with pigmented hair. It helps indicate whether an animal is heterozygous or homozygous and helps estimate transmission. Complementary to, not a substitute for, clinical examination.
Inheritance patternAutosomal dominant with relevant zygosity. Homozygosity was considered lethal; recent studies demonstrate viable homozygotes, so the classic lethality is under discussion.
Gene / MutationKIT: roan is associated with variants and haplotypes of the KIT gene, with no single confirmed causal mutation. Everts and colleagues (2025) defined haplotypes RN1 and RN2 (several variants) and RN3 (variant chr3:79656505G>A) in the American Quarter Horse; associations have also been described in Noriker (SNP in intron 17 of KIT) and Icelandic horses. Definitive causality remains to be confirmed, so the result should be interpreted as indicative of the haplotype, not as a definitive diagnosis. Reference variant NAS TB-T2T Chr3:83651836 (KIT exon 15 c.2181G>A, p.Val727Val, synonymous).
PenetranceIncomplete and variable; the number of copies/haplotypes and other modifiers influence the intensity. The classically described lethality of the homozygote has not been confirmed in recent studies.
Sample type0,5-1 ml sangre-EDTA o 20-30 pelos de la crin o la cola
Codefjte
Turnaround time30 days
Price85,54 €
Breedstodas las razas de caballo

Incidence

Applicable breeds: Quarter Horse, Icelandic, Noriker, Belgian and others. Frequencies: limited data; the described haplotypes explain only part of roan horses.

Clinical signs

• Uniform mixture of white and pigmented hair over the body, without defined patches.
• The mane and tail usually keep the base colour.
• The intensity varies with age and season; it does not affect the skin.

History

Roan was linked to the linkage group of the extension locus and later to the KIT gene (Marklund 1999). In 2020 Grilz-Seger (Noriker) and Voß (Icelandic) described associated KIT variants and challenged the classic lethality of the homozygote. In 2025 Everts and colleagues defined haplotypes RN1, RN2 and RN3.

Breeder management

• Interpret zygosity with caution: do not assume that the homozygote is lethal.
• Do not mate two roan horses if you do not wish to increase the intensity of the mottling.
• Confirm the haplotype (RN1/RN2/RN3) according to the breed, as the test may not cover all variants.
• A negative result does not rule out the phenotype if the breed's causal variant is not included.

Specialist notes

Differential diagnosis with grey (STX17, which greys with age), sabino and true roan. Roan is not associated with deafness or loss of skin pigment. The molecular causality remains open.

References

1. Marklund 1999, Close association between sequence polymorphism in the KIT gene and the roan coat color in horses (PMID 10051325); OMIA:001216-9796.
2. Grilz-Seger 2020, A genome-wide association analysis in Noriker horses identifies a SNP associated with roan (PMID 32303326); OMIA:001216-9796.
3. Voß 2020, Coat color roan shows association with KIT variants and no evidence of lethality (PMID 32580410); OMIA:001216-9796.
4. Ludwig 2022, Roan coat color in livestock (review) (PMID 35811453).
5. Everts 2025, Two genetic haplotypes associated with roan coat color (RN1/RN2) (PMID 40564257); OMIA:001216-9796.
6. Everts 2025, Identification of a novel haplotype associated with roan coat color (RN3) (PMID 40867714); OMIA:001216-9796.
Price: 85,54 € · Turnaround time: 30 days

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