What is Hyperekplexia?

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  • Written By: Eric Stolze
  • Edited By: Lauren Fritsky
  • Last Modified Date: 12 September 2019
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Hyperekplexia is a genetic condition that typically occurs in infants and tends to cause an exaggerated reaction to loud noises or other unexpected external stimuli. This medical problem is also known as Kok disease, stiff baby syndrome and exaggerated startle reflex. In most cases, patients with this disorder become very startled, their muscle tone increases and their bodies become abnormally rigid. This unusual rigidity may cause some babies to stop breathing and can ultimately result in death if a patient does not resume breathing quickly enough.

Muscle twitches often occur in babies with hyperekplexia as they fall asleep, and an infant’s legs and arms can move abnormally during sleep. Some deaths that are attributed to sudden infant death syndrome (SIDS) may be caused by hyperekplexia. In some case, an infant may develop spasms of the neck muscles and the limbs after the child is tapped on the nose. Babies with this genetic disorder may have epileptic seizures in rare instances.

Most patients with hyperekplexia tend to have diminished symptoms by the time they reach age 1. In cases where older patients still experience rigidity from this disease, they may fall down from sudden rigidity and continue to startle easily from unexpected external stimuli. Patients who have epileptic seizures with this condition typically continue to experience seizures throughout their lives. Individuals with hyperekplexia often have a dislike of crowded environments.


Hyperekplexia is caused by an abnormality in a patient’s genes usually related to mutations that develop in a gene that influences glycine production. Glycine is a brain chemical and neurotransmitter that transmits nerve signals throughout the brain and central nervous system. Mutations may also affect the ability of glycine receptors to respond to nerve signals transmitted with glycine. Patients can inherit a mutation in a gene that causes hyperekplexia, or they may develop a genetic mutation without a family history of the disorder, usually as a result of an external cause such as a brain trauma. Some parents pass on a defective gene to their offspring that causes this disease even when neither parent has signs of it.

Physicians may treat hyperekplexia patients with clonazepam, a prescription drug that generally improves the function of gamma-aminobutyric acid (GABA), another neurotransmitter. Other drugs may also be used to treat this condition as recommended by a doctor. Some medical doctors use a technique called the Vigevano maneuver to reduce symptoms during a startle response. A doctor typically flexes a patient’s head and limbs toward the trunk with this maneuver.


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Post 1

I'm 13 and I have this. It stinks. My siblings will always tease me about it and I just hate them so much for it. Every time they startle me, my heart feels like it stops but even the littlest things scare me, like if something falls in the distance.

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