Researchers from Wageningen University, Utrecht University and the University Medical Center Utrecht have discovered the mutation causing hydrocephalus (water on the brain) in Friesian horses. The discovery of this lethal mutation was recently published in BMC Genomics. Prior to the final approval of the publication, this unique consortium developed a DNA test, in collaboration with ‘Dr. van Haeringen Laboratorium (VHL)’ in Wageningen. With this test 865 Friesian horses have so far been screened to identify carriers of this mutation, such that so-called risk-matings for hydrocephalus can be avoided.
What is hydrocephalus?
Hydrocephalus means more medically, an abnormal accumulation of cerebrospinal fluid in the brain. Affected foals are often born too early and not alive. Noticeable on the outside of these foals is the severe distension of the skull. Due to the large size of the foals’ skull, dams have difficulties in giving birth to these foals what eventually could lead to fatal complications.
Hydrocephalus is mainly observed in Friesian horses, although it is difficult to get an estimate of the number of affected foals born per year. Inbreeding in the Friesian horse population and the widespread use of some influential ancestors have likely contributed to the spread of hydrocephalus in the Friesian horse population.
Similarity with human disease!
The genetic material, of 13 foals with hydrocephalus and 69 healthy control horses showed that the gene responsible for hydrocephalus in Friesian horses is located on chromosome 1. After studying the genetic material of several foals with hydrocephalus and healthy control horses in much more detail a mutation in the gene B3GALNT2 proved to be consistently associated with hydrocephalus.
This mutation causes a syndrome in humans called MDDGA11. Patients with MDDGA11 show muscle weakness with brain and eye defects. The syndrome included hydrocephalus in 4 out of 6 patients that were investigated. The mutation identified in one patient was exactly the same as the mutation that we discovered in Friesian horses. This similarity served as an extra proof that the mutation discovered in Friesian horses indeed causes hydrocephalus.
DNA test and breeding
The DNA test has already been used to screen 865 Friesian horses. 17% of the screened horses turned out to be carrier of the mutation. When mated with another carrier, there is a 25% chance of a hydrocephalus foal. The fastest but not most sensible way to reduce hydrocephalus in the population is to eliminate all carriers from breeding. However, this will undesirably increase inbreeding. For now, it is therefore advised not to mate 2 carriers.
Future scientific research
The Royal Friesian horse studbook (KFPS) is actively investigating more genetic diseases, to be able to effectively reduce prevalence of these diseases by breeding in Friesian horses.
The scientific paper published in BMC Genomics can be found here.