Hyperekplexia

Hyperekplexia
Synonyms	Startle disease, exaggerated startle reflex
Pronounce
Field	Neurology, Genetics
Symptoms	Exaggerated startle reflex, muscle stiffness (hypertonia), sudden falls, apnea (in infants)
Complications	Risk of injury due to falls, breathing difficulties in neonates
Onset	Typically at birth or in early infancy
Duration	Lifelong, may improve with age
Types	Familial hyperekplexia, sporadic hyperekplexia
Causes	Mutations in genes encoding glycine receptor components (e.g., GLRA1, GLRB, SLC6A5, GPHN)
Risks	Inherited in an autosomal dominant or autosomal recessive pattern
Diagnosis	Clinical examination, genetic testing, electromyography (EMG)
Differential diagnosis	Epilepsy, infantile spasms, startle epilepsy, tetanus
Prevention	None
Treatment	Supportive care, physical therapy, safety measures
Medication	Clonazepam (commonly used to reduce startle response)
Prognosis	Varies; often improves with age, though startle response may persist
Frequency	Rare
Deaths	Rare, typically due to apnea or falls in early infancy

Hyperekplexia is a rare neurological disorder characterized by an exaggerated startle reflex. This condition is also known as "startle disease" or "stiff baby syndrome" when it presents in infants. The disorder is primarily genetic and can manifest in both hereditary and sporadic forms.

Signs and Symptoms

Individuals with hyperekplexia exhibit an abnormal startle response to unexpected stimuli, such as loud noises or sudden movements. This response is often accompanied by a temporary muscle stiffness or rigidity, which can lead to falls and injuries. In infants, the condition may present as excessive muscle tone and a tendency to startle easily.

Infantile Hyperekplexia

In newborns, hyperekplexia can be identified by a pronounced startle response and hypertonia, which is an increased muscle tone. Affected infants may appear stiff and have difficulty with normal movements. The exaggerated startle reflex can interfere with feeding and breathing, leading to potential complications.

Adult Hyperekplexia

In adults, the symptoms of hyperekplexia may include sudden falls due to the startle response, which can occur without warning. The condition can also cause anxiety and social withdrawal due to the unpredictability of the startle episodes.

Causes

Hyperekplexia is often caused by mutations in the GLRA1 gene, which encodes the alpha-1 subunit of the glycine receptor. Glycine is an important neurotransmitter in the central nervous system, and its receptor plays a crucial role in inhibitory neurotransmission. Mutations in this gene can disrupt normal receptor function, leading to the symptoms of hyperekplexia.

Diagnosis

The diagnosis of hyperekplexia is based on clinical evaluation, family history, and genetic testing. Electromyography (EMG) and nerve conduction studies may be used to assess the startle response and muscle activity. Genetic testing can confirm mutations in the GLRA1 gene or other related genes.

Treatment

Treatment for hyperekplexia often involves the use of medications to reduce the startle response and muscle stiffness. Clonazepam, a benzodiazepine, is commonly prescribed to help manage symptoms. In some cases, other medications such as valproic acid or carbamazepine may be used.

Prognosis

The prognosis for individuals with hyperekplexia varies. With appropriate treatment, many individuals can manage their symptoms effectively and lead relatively normal lives. However, the risk of injury from falls remains a concern, and ongoing medical management is often necessary.

Related pages

• Neurological disorder
• Startle reflex
• Glycine receptor
• Genetic disorder

External links

• GeneReview/NIH/UW entry on Hyperekplexia

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