A research team from the Universities of Göttingen and Halle in Germany has been able to prove that the genetic disease Warmblood Fragile Foal Syndrome (WFFS) did not stem from the English thoroughbred stallion Dark Ronald XX, which had been the assumption until now. The results have been published in the journal Animal Genetics.

Warmblood Fragile Foal Syndrome is a severe, usually fatal, genetic disease that manifests itself after birth in affected horses. Due to the defect, the connective tissue is unstable and under even the lightest force, the skin tears from the tissue underneath and the joints can suffer dislocation. It can also cause miscarriages and infertility in affected mares and stallions.

The disease itself is not new and probably originated in the middle of the 18th century. Since then, all breeding animals have been consistently tested for the genetic defect. There is a comparable genetic disease in humans known as Ehlers-Danlos syndrome which shows similar symptoms.

WFFS manifests as extremely delicate skin that tears or ulcerates easily and loose, hyperextensible joints – providing the foal actually survives the birth. There is no cure, with euthanasia as the only humane option. (Laboklin photo)

The gene responsible, PLOD1, was identified in 2012. PLOD1 normally ensures that collagen molecules in the skin and connective tissue can bind to form a stable network. The mutation in the PLOD1 gene prevents “cross-linking” which is needed for stable collagen.

The exact origin of the mutation was previously unclear. Since the spread of the genetic defect is also a problem in horse breeding in Germany, the Vereinigte Informationssysteme Tierhaltung (IT-Solutions for Animal Production) in Verden 2019 determined the possible origin of the genetic defect from the test results of around 2,000 horses and their pedigree records. The investigation concluded that the genetic defect was probably due to “patient zero,” the English thoroughbred stallion Dark Ronald XX (1905-1928) or his father, Bay Ronald XX, and the defect then spread through their offspring.

The current research led by the University of Göttingen calls this theory into question. “We have now succeeded in proving that Dark Ronald XX was not a carrier of the PLOD1 mutation and can therefore be excluded as the original source of this genetic defect,” says Professor Bertram Brenig, director of the Institute of Veterinary Medicine at the University of Göttingen and lead author of the study. Further investigation points to the WFFS‐causing variant most likely originating from an unidentified Hanoverian stallion from the F/W line born in 1861.

Dark Ronald XX was an important thoroughbred stallion with highly-prized heritable characteristics who had a great influence on German horse-breeding. He was sold to Germany in 1913 and stood at stud first in Graditz and later in Altefeld. In 1928, he was brought to the veterinary clinic at the University of Halle for treatment of intestinal colic, where he died. Since then his skeleton, heart and skin have been kept in one of the natural science collections of the Martin Luther University Halle-Wittenberg.

“This is most fortunate, as it has allowed us to examine Dark Ronald XX directly for the presence of the PLOD1 mutation,” says Brenig. The scientists were thus able to examine small pieces of Dark Ronald XX’s skin and come to their conclusions that he was not a carrier.

Read more about Warmblood Fragile Foal Syndrome here.