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LWFS Lethal White Foal Syndrome

Name: LWFS Lethal White Foal Syndrome
Brand: Equigerminal
Price: 43.05 EUR

Test that shows if your horse carries the gene change that, with two copies, gives a white foal that cannot...

€43.05 Mat TVA

About

This test shows whether your horse carries the gene change behind the frame overo coat pattern. A foal that inherits it from both parents has Lethal White Foal Syndrome, a fatal condition.

It is for any horse with the frame overo pattern, in any breed or registry, and for any horse that may be bred to one.

Why test?

Breeding. A lethal white foal is produced only when both parents pass the change on. Knowing the result of both parents tells you what each mating can produce.

Buying and selling. The result is objective, permanent information you can show a buyer.

Explaining a white foal. Not every white foal has this condition. The test shows whether this gene change is the cause.

Clinical signs

Signs are seen only in newborn foals that inherited the change from both parents:

Born looking almost pure white
Unable to pass droppings, with signs of colic in the first hours of life, because the nerves that drive the last part of the bowel never developed
Death within the first 72 hours. Affected foals are usually put down sooner, for humane reasons.

The condition always kills, and there is no treatment. The diagnosis is made by a veterinarian, combining the examination and this genetic result.

Transmission

This variant behaves in two ways at once. For the coat pattern it is dominant: one copy is enough to give the frame overo pattern. For the fatal disease it is recessive: two copies are needed, one from each parent. The gene is not on a sex chromosome, so colts and fillies are affected equally.

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
n/O x n/O gives 25% n/n, 50% n/O, 25% O/O

These are chances for each foal, and they are the same for every pregnancy, whatever happened before.

Prevention

Prevention is a breeding decision, and a completely effective one.

Breeding. Test both parents before mating and never mate two carriers. A carrier mated to a partner that tested negative cannot produce an affected foal.

Keeping the pattern. Carrying the change is not a reason to leave a horse out of breeding. Testing lets you breed for the frame overo pattern safely.

Do not rely on appearance. Some frame overo horses do not carry the change, and solid-coloured and tobiano horses have been found to carry it. Only a test result rules it out.

Results

n/n: negative. No copy of the frame overo variant. Cannot pass it on and cannot produce a lethal white foal.

n/O: carrier (frame overo). One copy. The horse is healthy and normally shows the frame overo pattern. Can pass the variant on.

O/O: affected. Two copies. The foal has Lethal White Foal Syndrome.

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.

In a newborn white foal, 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.

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

🛒 Buy the test: select and buy the test online.

📧 Receive the instructions: after payment is confirmed, you receive the sample collection instructions by e-mail.

📄 Complete the form: print and complete the submission form with the animal’s identification.

✨ Collect the sample: pull 20 to 40 hair roots with the bulb and stick them in the marked area of the form, or ask your veterinarian to collect blood in a K3-EDTA tube.

📮 Send it to the laboratory: Equigerminal, S.A., HIESE, Rua da Quinta do Sobreiro, 25, Quinta Vale do Espinhal, 3230-343 Penela, PORTUGAL.

📊 Receive the report: the certified report is issued as soon as the analysis is validated.

FAQs

At what age can a horse be tested?
Any age. The genotype is fixed at conception and never changes, so one test lasts for life.

Does this test detect other white patterns?
No. It does not detect tobiano, sabino, splashed white or any other white pattern.

Can a carrier have any health problem?
Carriers live a normal life, but those with a great deal of white on them are more often born deaf.

For Professionals

Genetic and clinical detail for veterinarians, geneticists and laboratories.

Gene / locus: EDNRB (endothelin receptor type B), 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: described in 1998 by three groups as Ile118Lys (Santschi et al., 1998; Metallinos et al., 1998) and as a dinucleotide mutation (Yang et al., 1998). The genomic record (delinsCT) and the cDNA record (delinsAG) describe the same change on opposite strands. Disease synonyms: overo lethal white foal syndrome (OLWS, OLWFS), lethal white overo (LWO); human homologue Hirschsprung disease.
Variant identifiers: no rs/EVA identifier listed in OMIA; OMIA variant 160.
Variant classification: not currently evaluated (ISAG/AVCG, per OMIA).
Mechanism: EDNRB steers the migration of one embryonic cell lineage that gives rise to both skin pigment cells and the enteric nerves of the gut wall. In heterozygotes, pigment cells fail to reach some areas, producing the white frame overo markings. Homozygous foals are almost entirely white and have myenteric aganglionosis with fatal functional intestinal obstruction (Santschi et al., 2001).
Inheritance: frame overo pattern autosomal dominant over solid colour; lethal white foal syndrome autosomal recessive (homozygotes only). OMIA code: A (autosomal).
Penetrance / expressivity: all OLWS foals tested were Lys118 homozygotes and no living homozygote was found (Santschi et al., 2001). The white pattern is incompletely expressed in heterozygotes: about 5% of phenotypic frame overos did not carry the allele, and two heterozygous Miniature Horses had no white markings (Santschi et al., 2001). Both 1998 American studies also found carriers among horses with no overo markings. 31 of 34 deaf or suspected-deaf American Paint Horses carried the variant (Magdesian et al., 2009).
Breeds with documented carriers or cases: American Paint Horse, Quarter Horse, Thoroughbred, Miniature Horse (OMIA variant record). Best documented in the American Paint Horse.
Allele / carrier frequencies: allele frequency 10.7% in 180 control American Paint Horses; not detected in 651 elite performance and 200 control American Quarter Horses (Tryon et al., 2009). 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-coloured horses of other breeds 0/55. In Brazil, estimated carrier frequency in American Paint Horses was 21.6% overall and 89.5% among overo horses (Badial et al., 2018).
Clinical / diagnostic notes for veterinarians: the laboratory genotypes this variant only (0, 1 or 2 copies); KIT, MITF and PAX3 white-spotting variants are not detected. In extensively white heterozygotes, hearing can be assessed by brainstem auditory-evoked response testing (Magdesian et al., 2009).

Key references:

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.
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.
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. 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. doi:10.2460/javma.235.10.1204.
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.
Badial PR, Teixeira RBC, Delfiol DJZ, da Mota LSLS, Borges AS (2018). Validation of high-resolution melting analysis as a diagnostic tool for endothelin receptor B mutation in American Paint horses and allele frequency estimation. Mol Cell Probes 41:52-56. doi:10.1016/j.mcp.2018.08.002.
Keppers HA, Gonda MG (2025). Lethal white foal syndrome: a review. Can J Anim Sci 105:1-8. doi:10.1139/cjas-2024-0077.