Short answer · Medically reviewed summary · Last updated: 2026-05-08
Hyperekplexia, also known as startle disease, is a rare neurological disorder characterized by an exaggerated, persistent startle reflex to unexpected auditory, tactile, or visual stimuli. Individuals living with Hyperekplexia often experience muscle stiffness (hypertonia) and brief episodes of involuntary muscle rigidity that can lead to sudden falls. What are the primary symptoms of Hyperekplexia? The hallmark of Hyperekplexia is an excessive startle response that does not diminish with repeated exposure to the stimulus.
What is Hyperekplexia
What is Hyperekplexia? Plain-language, medically reviewed definition plus the lived reality told by patients.
Hyperekplexia, also known as startle disease, is a rare neurological disorder characterized by an exaggerated, persistent startle reflex to unexpected auditory, tactile, or visual stimuli. Individuals living with Hyperekplexia often experience muscle stiffness (hypertonia) and brief episodes of involuntary muscle rigidity that can lead to sudden falls.
What are the primary symptoms of Hyperekplexia?
The hallmark of Hyperekplexia is an excessive startle response that does not diminish with repeated exposure to the stimulus. Unlike a typical startle reflex, this reaction can cause a temporary, generalized muscle spasm that leaves the person unable to move for several seconds. In infants, Hyperekplexia is often identified by extreme stiffness shortly after birth, which can sometimes lead to dangerous periods of apnea (temporary cessation of breathing).
What causes Hyperekplexia?
Hyperekplexia is primarily caused by genetic mutations that impair the body's ability to process the neurotransmitter glycine. Glycine acts as a "braking system" for the nervous system; when this system fails, the brain and spinal cord become over-excitable. The condition is most commonly associated with mutations in the GLRA1 gene, though other genes like GLRB and SLC6A5 are also involved. It is typically inherited in an autosomal dominant or recessive pattern.
How common is this condition?
Hyperekplexia is considered an ultra-rare disorder. While the exact global prevalence is unknown due to underdiagnosis, it is estimated to occur in approximately 1 in 40,000 to 1 in 50,000 individuals. Within the DiseaseMaps community, 56 people with Hyperekplexia have connected to share their experiences and navigate the challenges of this diagnosis.
Key clinical features and diagnosis
- Exaggerated startle: Reflexes are disproportionate to the stimulus.
- Neonatal hypertonia: Persistent stiffness in newborns that typically improves with age.
- Nocturnal myoclonus: Sudden, jerky muscle movements during sleep.
- Differential diagnosis: It is frequently misdiagnosed as epilepsy; however, EEG readings in Hyperekplexia patients are typically normal, distinguishing it from seizure disorders.
Next steps
- Consult a neurologist or clinical geneticist to confirm a diagnosis through genetic testing.
- Speak with your physician about the use of clonazepam, which is often the first-line treatment for managing symptoms.
- Join the 56 members of the DiseaseMaps.org Hyperekplexia community to connect with others who understand the day-to-day reality of the condition.
Medical disclaimer: This content is for informational purposes only and does not constitute professional medical advice, diagnosis, or treatment; always seek the guidance of your physician regarding any medical condition.
References
- NIH Genetic and Rare Diseases Information Center (GARD): Hyperekplexia
- Orphanet: Hyperekplexia (ORPHA:392)
- OMIM (Online Mendelian Inheritance in Man): #149400 (Hyperekplexia 1)
- PubMed: Clinical and genetic overview of hereditary hyperekplexia
