Irish Wolfhound Startle Disease (SD) – Hyperekplexia

One condition that affects the Irish Wolfhound is a neurological disorder called Hyperekplexia or Irish Wolfhound Startle Disease (SD). It is a hereditary disorder that sees Wolfhounds being startled by noise or when they are touched. The condition is known to affect people as well as animals with horses and cattle as well as dogs suffering from a very similar type of disorder. The actual cause and genetics behind hyperekplexia remain unknown although studies have shown that the mode of inheritance as well as any symptoms associated with it can differ by varying degrees.

The genes responsible for hyperekplexia

As previously mentioned, research has established that the genes responsible for the disorder are as follows:

• GLRB
• SLC6A5
• GPHN
• ARHGEF9

It is worth noting that all the above genes play an essential part in glycine neurotransmission which are also referred to as chemical messengers that send signals from one nerve cell to another which could be a muscle cell, gland cell or another “target” neuron. Glycine is the smallest of 20 vital amino acids and its principle role in the body is to act as a building block for many natural products as well as being a precursor to proteins. It also plays a vital role as an “inhibitory neurotransmitter” in a dog’s central nervous system and more especially in their brainstems, retinas and spinal cords.

When genes are negatively impacted by any sort of mutation in their encoding glycine transporters or receptors, the result is a malfunction in the process and this causes a dog to suffer the symptoms of hyperekplexia/Startle Disease which includes displaying a startled reflex to certain outside stimulus.

A startle reflex plays a vital role in protecting the more vulnerable areas of the body namely the back of a dog’s neck which causes them to shy away and their eyes causing them to blink. As such, the reflex allows for a dog to escape any perceived sudden threat.

The symptoms associated with hyperekplexia

Irish Wolfhounds suffering from the condition show signs of there being something wrong when they are still young which can be anything from 5 to 7 days of being born. Their symptoms typically include the following:

• Rigidity
• Tremours

It is worth noting that when a puppy is asleep or relaxed, their symptoms cease to be evident. However, when awake, puppies cannot stand up and they extend all 4 legs in a rigid position. Also, when a puppy suckles, they may even stop breathing and turn blue. Puppies suffering from the condition are typically smaller and they weigh a lot less than other puppies in the litter.

Diagnosing the condition

A vet would need to carry out a thorough examination and take a biopsy of skin tissue to establish a definitive diagnosis. Studies have shown that abnormalities tend to be more severe in male Irish Wolfhound puppies than in their female counterparts.

The mode of inheritance and genetics

Research into the disorder, as previously mentioned has identified the genes responsible for hyperekplexia and that it is inherited by puppies as an “autosomal recessive trait”. As such, a dog could be either “clear, a carrier of affected”. Each parent dog would carry one of the mutated genes and puppies would need to inherit 2 copies of the gene mutation from each of the parent dogs to be affected by the condition.

Should two “carriers” be mated, although they show no signs of suffering from the disorder, their offspring would be at risk of inheriting Startle Disease with the statistics being as follows:

• 25% of puppies could be affected
• 50% of puppies could be asymptomatic carriers
• 25% of puppies could be carriers or they could be unaffected by the disorder

Prognosis

It is much kinder to put Irish Wolfhound puppies diagnosed as suffering from Startle Disease to sleep because of how the disorder affects the quality of their lives which a vet typically recommends in the first few months of their lives.

Testing for Startle Disease (SD)

Irish Wolfhounds can be DNA tested to see if they carry the SLC6A5 gene which would establish if they are carriers of the disorder.

It is worth noting that there could be other reasons why a dog suffers from the condition and that an Irish Wolfhound that tests “normal” would not have another type of gene mutation or some other gene that could cause them to suffer from a similar disorder.