Introduction
Hyperekplexia is a rare genetic disorder that affects both males and females and is most often present at birth. However, the disorder may not manifest itself until adolescence or adulthood in some people. In the United States, one in every 40,000 people suffers from hyperekplexia.
What Is Hyperekplexia?
The National organization of rare diseases (NORD) defines hyperekplexia (HPX) as a hereditary neurological disorder. The condition is considered uncommon. HPX can occur in utero, as well as in newborns and infants. Therefore, children and adults can both be affected by the disorder. HPX may also be known by other names, such as:
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Familial startle disease.
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Hereditary hyperekplexia.
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Startle syndrome.
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Stiff-baby syndrome.
People with HPX have a heightened startle response to loud noises or other unexpected stimuli. As a result, infants have hypertonia or increased muscle tone. Infants experience extreme muscle tension following a startle response and cannot move. In addition, some infants may stop breathing during an episode of rigidity, which can result in a potentially fatal situation.
Furthermore, rigidity can cause some people to collapse without losing consciousness. People suffering from HPX may exhibit gait abnormalities, overactive reflexes, and other signs and symptoms.
What Causes Hyperekplexia?
HPX affects both men and women. Although it is most commonly seen in newborns, it can appear later in life, like in adolescence or adulthood. Most HPX cases occur due to inheriting an autosomal dominant trait, which means that only one mutated gene from a parent is required to develop the condition.
GLRA1 gene mutations cause the majority of cases of hyperekplexia. The GLRA1 gene codes for one component of the glycine receptor protein, the alpha (α)1 subunit. When this protein binds to glycine, signaling between cells is inhibited. Mutations in the GLRA1 gene result in the production of a receptor unable to respond to glycine. As a result, glycine is unable to regulate signaling in the spinal cord and brainstem. If glycine production is reduced or receptors are damaged, nerve cells are unable to regulate their reactivity and, as a result, respond to stimuli exaggeratedly. Mutations in other genes cause the remaining cases of hyperekplexia.
An autosomal recessive pattern and a further mutation are other possible causes of HPX. A person with an autosomal recessive pattern inherits two mutated genes, one from each parent, and the parents may not exhibit any signs or symptoms of the disorder. The genetic variant arises spontaneously in the early stages of an individual's development with new mutations.
What Are The Symptoms Of Hyperekplexia?
Individuals' overall severity of the condition can vary greatly. Although symptoms persist into adulthood, they are most common in infants and children. The most common symptom of HPX is an exaggerated startle reaction in response to a sudden stimulus.
Examples of stimuli include sounds, an unexpected touch, a surprise movement such as a bump, and unexpected sightings of people or other objects. Once the response is activated, the person experiences rigidity or muscle stiffness and is likelier to fall. There is also a risk of injury because they cannot catch themselves and break the fall with their arms.
Other symptoms associated with HPX include:
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The arching of the head accompanies the startle reaction.
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Jerking movements following a startle reaction or when attempting to fall asleep.
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Severe muscle tension is most likely noticed in infants.
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Lack of movement or slower-than-normal movement of infants.
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Overactive reflexes.
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Intermittent apnea (pause in breathing).
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Unsteady gait.
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Dislocated hip at birth.
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Inguinal hernia (bulging of a part of the soft tissue in the abdomen).
According to Genetics Home Reference, a division of the National Library of Medicine, in most people, with hyperekplexia, the symptoms subside by age one. However, this is not the same for everyone, and some older people will continue to have a hyper-reactive startle response, rigidity episodes, falls, and movements while sleeping. They can also experience overstimulation in crowds or noisy environments.
How Is Hyperekplexia Diagnosed?
If an infant has an overactive startle response, increased stiffness, or a decreased ability to engage in voluntary movements, the healthcare provider may suspect HPX. This diagnosis is frequently considered in the differential diagnosis of infants who present with spells suggestive of seizures. Because HPX is usually inherited, the doctor will examine the family's medical history for clues to possible genetic diseases. The clinical presentation of HPX may be used to make an initial diagnosis.
To confirm, the doctor may advise tests such as electromyography (EMG), which examines how well the body's nerves control the muscles, and electroencephalography (EEG), which analyses the electrical activity occurring in various parts of the brain.
Additionally, genetic testing can be used to confirm a diagnosis and aid in discovering the cause. Finally, because genetic testing is constantly evolving, new testing may emerge later in life to help clarify any concerns.
How Is Hyperekplexia Treated?
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Treatments frequently aim to manage HPX symptoms, particularly the overactive startle response and muscle systems. Unfortunately, there is no cure for the condition. Anti-anxiety and anti-spastic medications such as Clonazepam and Diazepam, as well as Carbamazepine, Phenobarbital, and others, may be used.
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As an adjunct therapy, physical or occupational therapy may alleviate symptoms and assess the need for assistive and adaptive equipment (strollers, walkers, seating, and positioning devices) to enhance one's quality of life. Cognitive behavioral therapy (CBT) can also help with anxiety reduction.
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When an infant has significant breathing difficulties, the doctor may recommend using a breathing or heart rate monitor to keep an eye on the child. Parents may also choose to learn infant CPR (cardiopulmonary resuscitation) so that they can assist their child in the event of an emergency.
Conclusion:
Hyperekplexia is a rare neurological condition characterized by hypertonia and startled responses to tactile or acoustic stimuli. Any unexpected diagnosis can be frightening, especially when involving a rare neurological disease. Connecting with people with similar disorders and symptoms is also a way to cope and find support. Among these are epilepsy, generalized anxiety, and TIC disorders (like Tourette syndrome). Finally, the more understanding of the condition and the treatment options available, the more one can feel in control of their health.
