UC Davis School of Veterinary Medicine Veterinary Genetics Laboratory

Warmblood Fragile Foal Syndrome Type 1

Introduction

Warmblood Fragile Foal Syndrome Type 1 (WFFS) is a fatal genetic defect of connective tissue characterized by hyperextensible, abnormally thin, fragile skin and mucous membranes (tissue that lines cavities and covers organs) that cause extensive lesions throughout the body. Other signs of the disease include hyperextension of limb articulations, floppy ears, hydrops (accumulation of fluid in fetus), subcutaneous emphysema, hematomas and premature birth. Signs of the disease are present from birth. Newborn foals have to be euthanized because of poor prognosis for an untreatable condition.

WFFS is caused by a mutation (c.2032G > A) in the PLOD1 gene (procollagen-lysine, 2-oxoglutarate 5-dioxygenase1) that codes for an enzyme important for biosynthesis of collagen, which are complex molecules that provide strength and support to many body tissues. The mutation impairs normal function of the enzyme, which leads to development of the disease. In humans, mutations in this gene are associated with a similar defect known as Ehlers-Danlos Syndrome Type VI.

WFFS is inherited as an autosomal recessive defect, which means that both males and females are equally affected and that two copies of the mutation (WFFS/WFFS) are needed to cause the disorder. Horses that carry one copy (N/WFFS) of this recessive mutation are normal but can transmit the mutation to 50% of their offspring.

The Veterinary Genetics Laboratory offers a DNA test for WFFS. The test benefits clinicians to help with diagnosis of WFFS. The test benefits breeders and owners to identify carriers of WFFS and to select mating pairs accordingly to avoid producing affected foals. Mating between two carriers has a 25% chance of producing affected foals.

Research at the VGL has identified a low carrier frequency of the WFFS mutation in Thoroughbreds.To date, no Thoroughbreds homozygous for the mutation have been detected. In studying over 700 horses, carrier frequency was 2.4%, meaning out of 200 horses approximately 5 would have one copy of the mutation. Investigating the WFFS allele and carrier frequencies in other breeds is is ongoing. Information about other breeds will be updated.

Testing recommendation: The test is presently recommended for all Warmblood/Sport Horse populations. The incidence of carriers in Warmblood horses is estimated to be around 9-11%. Additionally, since the WFFS allele has also been detected in the Thoroughbred, albeit at a low frequency, testing could inform mating decisions to avoid breeding carriers.

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Results reported as:

N/N No copies of the WFFS mutation; animal is normal.
N/ WFFS 1 copy of the WFFS mutation; animal is normal but is a carrier. Horse can pass on the mutation to 50% of offspring.
WFFS/WFFS 2 copies of the WFFS mutation; horse is affected.

References:

Winand N. Identification of the causative mutation for inherited connective tissue disorders in equines. United States Department Of Commerce Application Number: 61/486,464; (Filing Date: May 16th, 2011).

Monthoux C, S Brot, M Jackson, U Bleul, J Walter. (2015). Skin malformations in a neonatal foal tested homozygous positive for Warmblood Fragile Foal Syndrome. BMC Veterinary Research 11:12. DOI 10.1186/s12917-015-0318-8.

Bellone, R. , Ocampo, N. , Hughes, S. , Le, V. , Arthur, R. , Finno, C. and Penedo, M. (2019), Warmblood fragile foal syndrome type 1 mutation (PLOD1 c.2032G>A) is not associated with catastrophic breakdown and has a low allele frequency in the Thoroughbred breed. Equine Vet J. doi:10.1111/evj.13182.

Note: The Warmblood Fragile Foal Syndrome test is a patented test in Germany, France and the UK. The Veterinary Genetics Laboratory does not offer the WFFS test to clients residing in Germany, France and the UK.

 
Veterinary Genetics Laboratory, Tel 530-752-2211, Email VGL