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FFS1 is a disorder of the connective tissue which causes hyperextensible joints and skin tearing in affected foals.

Full name

Fragile Foal Syndrome 1

Breeds known to be affected

FFS1 is most commonly found in Warmblood breeds but has been identified in many other breeds, including Thoroughbreds, at very low frequency.

Inheritance pattern

Autosomal recessive


FFS1 is a fatal connective tissue disorder that causes the skin to be thin, hyper-extensible (fragile) and easily torn. Other clinical signs include swelling and haematoma, joint laxity and possibly abortions and premature births. Foals are severely affected and euthanised due to a poor prognosis for life.

FFS1 is caused by a mutation in the PLOD1 gene and is autosomal recessive, so affected horses will have inherited the defective allele from each parent (FFS1/FFS1). If a horse is a carrier (n/ FFS1), it will not show any clinical signs of FFS1. However, there is a 50% chance it will pass the variant to its offspring, so mating to other carriers should be avoided to prevent the birth of an affected foal.

Whilst this disease is primarily recognised in Warmblood/Sport horses, which led to its original name of Warmblood Fragile Foal Syndrome; according to the latest research the mutation has been seen at very low frequencies in other breeds including Appaloosa, Haflinger, Knabstrupper, Mustang, Paint Horse, Quarter Horse and Thoroughbred. This indicates that the mutation originated a long time ago. 

Interpretation of results

n/n: Horse does not carry the mutation associated with FFS1.

n/FFS1: Horse has one copy of the mutation associated with FFS1.

FFS1/FFS1: Horse has two copies of the mutation associated with FFS1.


Monthoux et al. Skin malformations in a neonatal foal tested homozygous positive for Warmblood Fragile Foal Syndrome. BMC Veterinary Research 2015; 11:12 doi: 10.1186/s12917-015-0318-8

Martin et al. Fragile Foal Syndrome (PLOD1 c.2032G>A) occurs across diverse horse populations. Animal Genetics 2021; 52:132-140 doi: 10.1111/age.13020

Reiter et al. Distribution of the Warmblood Fragile Foal Syndrome Type 1 mutation (PLOD1 c.2032G>A) in different horse breeds from Europe and the United States. Genes 2021; 11:1518 doi: 10.3390/genes11121518

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