O Frame Overo Pattern
Finds out whether your horse carries frame overo, the EDNRB variant Ile118Lys. One copy gives the frame overo coat pattern...
€43.05 Inkl. mva.
About
This test shows whether your horse carries frame overo, a white spotting pattern, and how many copies it has. The same gene change causes Lethal White Foal Syndrome, a fatal condition of newborn foals.
It is for anyone breeding spotted horses, or horses from spotted lines, in the many breeds where frame overo occurs.
Why test?
Breeding. Knowing the result of both parents before the mating lets you avoid a lethal white foal.
Confirming a frame overo. Frame overo, splashed white and sabino can look alike. The test tells you whether the frame overo variant is really there.
A white newborn foal. Other genes can also make a foal white and healthy. The test tells them apart.
Registration and sale. The result is objective information you can show a buyer.
Clinical signs
No copy: no frame overo pattern. The horse can still have white from other genes.
One copy: the frame overo pattern, in a healthy horse.
- White patches with jagged, irregular edges, mostly on the sides of the body and neck
- The white rarely crosses the back, so the horse looks framed by colour
- The legs are usually coloured
- The face often has a lot of white, and blue eyes are common
- Some carriers show very little white, or none at all, and a tobiano pattern can hide it completely
Two copies: Lethal White Foal Syndrome.
- The foal is born all white or nearly all white, often with blue eyes
- The nerve cells that move food through the end of the small intestine and the large intestine are missing, so the foal cannot pass manure
- Colic starts within the first day, usually within 12 to 24 hours of birth
- The foal dies within days. Surgery has been tried without success, and there is no treatment. Your veterinarian will advise on ending the foal's suffering
- At least some affected foals are also deaf
Deafness in adults. Deafness has been found in horses carrying frame overo, mostly those with splashed white or mixed patterns. The variant on its own does not necessarily cause it.
Transmission
The pattern is dominant, the lethal disease is recessive. One copy gives the frame overo pattern. Only a foal with two copies, one from each parent, has Lethal White Foal Syndrome. The gene is not on a sex chromosome, so colts and fillies are the same.
What each mating can produce:
- n/n x n/n gives 100% n/n
- n/n x n/O gives 50% n/n, 50% n/O: no lethal white foals
- n/O x n/O gives 25% n/n, 50% n/O, 25% O/O: one foal in four has Lethal White Foal Syndrome
These chances apply to each foal and are the same for every pregnancy, whatever happened before. Foals with two copies do not survive to breed, so every relevant mating is one of the three above.
Prevention
Lethal white foals are completely preventable by testing before mating.
- Never mate two carriers
- Mate a carrier only with a partner that tested negative
- Test every spotted breeding horse, including tobianos and solid-coloured horses from spotted lines, not only the obvious frame overos
- Test the foals you keep for breeding, so the next generation is known too
A carrier does not need to leave the breeding programme. Bred only to partners that tested negative, it keeps its bloodline and its pattern.
Results
n/n: no copy. Cannot pass frame overo on.
n/O: one copy, carrier. Passes the variant to about half of its foals.
O/O: two copies, Lethal White Foal Syndrome. If this is the result of a newborn foal, contact your veterinarian at once. An adult horse cannot be O/O, so this result on an adult points to a sample or identification error and should be checked.
Sample
Hair roots: 20 to 40 hairs pulled (not cut) from the mane or tail, with the roots attached. Tape them inside the marked area of the printable sample submission form. Hairs without roots cannot be analysed.
Blood: 5 mL of whole blood in a K3-EDTA tube, collected by a veterinarian. Label the tube with the horse's name and send it with the submission form.
Newborn white foal: ask your veterinarian. Blood or tail hair roots can be taken straight away.
Keep samples dry and at room temperature, and do not freeze them. Do not send hair that is wet, mouldy or soiled with bedding or faeces.
Send your sample by regular mail or express delivery to:
Equigerminal Lab HIESE
Rua da Quinta do Sobreiro Nº25
3230-343 Penela, Portugal
Turnaround
Standard processing: results within 5 to 10 working days of the sample arriving at the laboratory. Shipping is arranged and paid for by the client, and transit time is not included in the 5 to 10 working days.
Samples that fail DNA extraction or amplification are repeated at no extra cost, which may add a few working days. We contact you if a new sample is required.
How it works
🛒 Purchase the test: select and buy the test online.
📧 Receive instructions: after payment confirmation you receive sample collection instructions by e-mail.
✨ Collect the sample yourself: pull 20 to 40 hair roots with the bulb attached, or ask your veterinarian to collect blood in a K3-EDTA tube.
📄 Complete the form: print and complete the submission form with the animal identification.
📮 Send it to the laboratory: Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.
📄 Receive your report: your certified report is issued as soon as the analysis is validated.
FAQs
Is this the same as your LWFS test?
Yes, both read the same variant. You only need one of them.
What does this test not detect?
Tobiano, splashed white, sabino, dominant white and the base colour.
At what age can a horse be tested?
Any age, including a newborn foal. The genotype is fixed at conception and never changes.
What should I order alongside it?
Tobiano, if the horse is spotted, and Extension and Agouti to predict the colour of the foal.
For Professionals
Genetic and clinical detail for veterinarians, geneticists and laboratories.
- Gene / locus: EDNRB (endothelin receptor type B), Frame overo (O) locus, ECA17.
- Variant: Ile118Lys (I118K), dinucleotide substitution, missense. HGVS (EquCab3.0): NC_009160.3:g.50503041_50503042delinsCT; NM_001081837.2:c.353_354delinsAG; NP_001075306.2:p.(Ile118Lys).
- Alternative designations: frame overo allele; described in 1998 as Ile118Lys (Metallinos et al.; Santschi et al.) and as a dinucleotide mutation (Yang et al.). Genomic delinsCT and cDNA delinsAG are the same change on opposite strands. Laboratory allele symbol: O.
- Variant identifiers: no rs/EVA identifier listed in OMIA; OMIA variant 160.
- Variant classification: not currently evaluated (ISAG/AVCG, per OMIA).
- Mechanism: EDNRB is needed in the embryo for the migration of pigment cell precursors and enteric nerve cells. Heterozygotes have skin patches without melanocytes; homozygotes also lack enteric neurons.
- Inheritance: pattern autosomal dominant; lethal white foal syndrome autosomal recessive. OMIA code: A (autosomal).
- Penetrance / expressivity: frame pattern is not expressed in all heterozygotes and may be masked by other white patterns; about 5% of phenotypic frame overos lacked the allele (Santschi et al., 2001). No living O/O horse was found.
- Breeds with documented carriers or cases: American Paint Horse, Quarter Horse, Thoroughbred, Miniature Horse (OMIA variant record); Pinto (Metallinos et al., 1998); Brazilian horse populations (Badial et al., 2018).
- Allele / carrier frequencies: carrier frequency by pattern (Santschi et al., 2001; 945 white-patterned and 55 solid horses): frame 178/188 (95%), frame blend 153/158 (97%), loud calico 37/37 (100%), medicine hat 9/13 (69%), tovero 49/84 (58%), calico 21/38 (55%), bald-faced 6/17 (35%), sabino 3/15 (20%), breeding-stock solid 26/146 (18%), splashed white 3/26 (12%), tobiano 11/109 (10%), minimal calico 6/67 (9%), non-frame blend 0/14, solid horses of other breeds 0/55. Allele frequency 10.7% in 180 control American Paint Horses (Tryon et al., 2009). In Brazil, 21.6% of horses tested carried the variant, and 89.5% of overo horses (Badial et al., 2018).
- Clinical / diagnostic notes for veterinarians: O/O foals are almost entirely white with myenteric aganglionosis and fatal functional intestinal obstruction. 31 of 34 deaf or suspected-deaf American Paint Horses carried the variant, mostly with splashed white or splashed white-frame blend patterns, extensive head and limb white and blue eyes (Magdesian et al., 2009); hearing can be assessed by brainstem auditory-evoked responses.
Key references:
- Metallinos DL, Bowling AT, Rine J (1998). A missense mutation in the endothelin-B receptor gene is associated with Lethal White Foal Syndrome: an equine version of Hirschsprung disease. Mamm Genome 9:426-431.
- Santschi EM, Purdy AK, Valberg SJ, Vrotsos PD, Kaese H, Mickelson JR (1998). Endothelin receptor B polymorphism associated with lethal white foal syndrome in horses. Mamm Genome 9:306-309. PMID 9530628.
- Yang GC, Croaker D, Zhang AL, Manglick P, Cartmill T, Cass D (1998). A dinucleotide mutation in the endothelin-B receptor gene is associated with lethal white foal syndrome (LWFS); a horse variant of Hirschsprung disease. Hum Mol Genet 7:1047-1052.
- Santschi EM, Vrotsos PD, Purdy AK, Mickelson JR (2001). Incidence of the endothelin receptor B mutation that causes lethal white foal syndrome in white-patterned horses. Am J Vet Res 62:97-103.
- Magdesian KG, Williams DC, Aleman M, LeCouteur RA, Madigan JE (2009). Evaluation of deafness in American Paint Horses by phenotype, brainstem auditory-evoked responses, and endothelin receptor B genotype. J Am Vet Med Assoc 235:1204-1211.
- Tryon RC, Penedo MCT, McCue ME, et al. (2009). Evaluation of allele frequencies of inherited disease genes in subgroups of American Quarter Horses. J Am Vet Med Assoc 234:120-125. doi:10.2460/javma.234.1.120.