Naked Foal Syndrome (NFS) is inherited as a monogenic autosomal recessive trait. A monogenic autosomal recessive trait is a trait that can be inherited from either parent. Two copies of the trait are required in order for a horse to develop symptoms. Monogenic traits are traits that are not necessarily dependent on inheritance, however. The gene can mutate on its own and the horse could still develop symptoms of NFS.
This disorder is caused by a nonsense variant G>T. This means that there was a premature stop in the DNA code. This premature stop cuts off up to 80% of the open reading frame (the DNA code) of the ST14 gene. This gene has a hand in the growth factor that stimulates hair growth within the skin. In humans, several genetic variants in the ST14 gene have been shown to be linked to an autosomal recessive form of congenital ichthyosis.
Horses affected by NFS are born hairless, and often die within days to months after birth. In most cases, it is unclear as to the reason for these early deaths. In some rare cases, hairless foals have survived up to 2.5 years. The first records of hairless Akhal-Teke foals date back to 1938. Since then, the number of hairless foals has increased steadily.
NSF is an autosomal recessive trait, meaning a foal can only be affected if the foal inherits the disease from both parents. Parents that are carriers (having only one copy of the mutated gene) do not have any symptoms associated with NSF. If two carriers are bred together, each foal born has a 25% chance of developing NFS. There is a 50% chance per foal born that they, too, will be carriers for NFS.
|Affected: Horse has two copies of the NFS mutation and will exhibit signs of the disorder.
|Carrier: Horse has one copy of the NFS mutation and can pass this gene on to any offspring.
|Clear: Horse is negative for the NFS mutation.
A Nonsense Variant in the ST14 Gene in Akhal-Teke Horses with Naked Foal Syndrome.
Bauer A, Hiemesch T, Jagannathan V, Neuditschko M, Bachmann I, Rieder S, Mikko S, Penedo MC, Tarasova N, Vitková M, Sirtori N, Roccabianca P, Leeb T, Welle MM.
G3 (Bethesda). 2017 Apr 3;7(4):1315-1321. doi: 10.1534/g3.117.039511. [PMID: 28235824]