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Disease Profile

Hereditary hyperekplexia

Prevalence estimates on Rare Medical Network websites are calculated based on data available from numerous sources, including US and European government statistics, the NIH, Orphanet, and published epidemiologic studies. Rare disease population data is recognized to be highly variable, and based on a wide variety of source data and methodologies, so the prevalence data on this site should be assumed to be estimated and cannot be considered to be absolutely correct.

<1 / 1 000 000

US Estimated

Europe Estimated

Age of onset






Autosomal dominant A pathogenic variant in only one gene copy in each cell is sufficient to cause an autosomal dominant disease.


Autosomal recessive Pathogenic variants in both copies of each gene of the chromosome are needed to cause an autosomal recessive disease and observe the mutant phenotype.


dominant X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome.


recessive Pathogenic variants in both copies of a gene on the X chromosome cause an X-linked recessive disorder.


Mitochondrial or multigenic Mitochondrial genetic disorders can be caused by changes (mutations) in either the mitochondrial DNA or nuclear DNA that lead to dysfunction of the mitochondria and inadequate production of energy.

Multigenic or multifactor Inheritance involving many factors, of which at least one is genetic but none is of overwhelming importance, as in the causation of a disease by multiple genetic and environmental factors.


Not applicable


Other names (AKA)

Startle disease, familial; Startle reaction, exaggerated; Exaggerated startle reaction;


Congenital and Genetic Diseases; Endocrine Diseases; Metabolic disorders;


Hereditary hyperekplexia is a nervous system disorder (neurological disorder), that is usually noticed shortly after birth. Symptoms in a newborn include generalized muscle stiffness while awake (hypertonia) and exaggerated startle reflex to unexpected loud noises, visual stimuli, or touch. Following the startle reaction, infants experience a brief period in which they are very rigid and are unable to move. During these rigid periods, some infants may stop breathing (apnea), which can be fatal and has been associated with sudden infant death syndrome (SIDS). Muscle stiffness usually fades completely during the first few years of life. However the exaggerated startle reflex and periods of rigidity may continue throughout a person's life. Depending on the severity of the continued symptoms, a child or adult with hereditary hyperekplexia may have an increased risk of falling or otherwise injuring themselves. In some cases, children with hereditary hyperekplexia may have mild developmental delays.[1][2][3] Abdominal hernias and congenital dislocation of the hip have also been associated with hereditary hyperekplexia.[2][3]

Diagnosis of hereditary hyperekplexia requires the three main features: generalized stiffness immediately after birth, excessive startle reflex to unexpected stimuli, and a short period of generalized stiffness following the startle response.[2][4] Of note, the results of routine blood tests, urinalysis, brain imaging studies, or EEG are usually normal.[1][2][3] Hereditary hyperekplexia has different inheritance patterns and is associated with changes (mutations) in at least five genes. Genetic testing is available to detect the genetic changes.[1][2][3][4] Clonazepam is the most commonly used treatment and successfully reduces symptoms in most people.[1][2][3]


This table lists symptoms that people with this disease may have. For most diseases, symptoms will vary from person to person. People with the same disease may not have all the symptoms listed. This information comes from a database called the Human Phenotype Ontology (HPO) . The HPO collects information on symptoms that have been described in medical resources. The HPO is updated regularly. Use the HPO ID to access more in-depth information about a symptom.

Medical Terms Other Names
Learn More:
80%-99% of people have these symptoms
Inflammation of the esophagus
Muscle twitch
Gastroesophageal reflux
Acid reflux
Acid reflux disease

[ more ]

Hiatus hernia
Stomach hernia
Increased reflexes
Joint stiffness
Stiff joint
Stiff joints

[ more ]

Muscle stiffness
Muscle rigidity
Involuntary muscle stiffness, contraction, or spasm
30%-79% of people have these symptoms
Gait disturbance
Abnormal gait
Abnormal walk
Impaired gait

[ more ]

Sleep disturbance
Difficulty sleeping
Trouble sleeping

[ more ]

Umbilical hernia
5%-29% of people have these symptoms
Hip dislocation
Dislocated hips
Dislocation of hip

[ more ]

Intellectual disability
Mental deficiency
Mental retardation
Mental retardation, nonspecific

[ more ]

Percent of people who have these symptoms is not available through HPO
Autosomal dominant inheritance
Autosomal recessive inheritance
Exaggerated startle response
Frequent falls
Decreased muscle movement
Decreased spontaneous movement
Decreased spontaneous movements

[ more ]

Infantile onset
Onset in first year of life
Onset in infancy

[ more ]

Inguinal hernia
Nocturnal seizures


Making a diagnosis for a genetic or rare disease can often be challenging. Healthcare professionals typically look at a person’s medical history, symptoms, physical exam, and laboratory test results in order to make a diagnosis. The following resources provide information relating to diagnosis and testing for this condition. If you have questions about getting a diagnosis, you should contact a healthcare professional.

Testing Resources

  • The Genetic Testing Registry (GTR) provides information about the genetic tests for this condition. The intended audience for the GTR is health care providers and researchers. Patients and consumers with specific questions about a genetic test should contact a health care provider or a genetics professional.


    Hereditary hyperekplexia is commonly treated with the anti-anxiety and anti-spastic drug clonazepam. Other medications which have been helpful for some people include carbamazepine, phenytoin, diazepam, valproate, 5-hydroxytryptophan, piracetam, phenobarbital, and fluoxetine.[3][4][5][6] In some cases, a combination of treatments (i.e. clobazam and clonazepam) may be needed.[6][7]

    If fear of falling has limited a person's willingness to go outside their home and/or caused the development of a cautious walking style, cognitive behavior therapy (CBT) and/or physical therapy, in combination with the medication to control the startle reflex and rigidity period, may help reduce anxiety, improve confidence in walking, and improve the person's quality of life.[3][4][5]


    Support and advocacy groups can help you connect with other patients and families, and they can provide valuable services. Many develop patient-centered information and are the driving force behind research for better treatments and possible cures. They can direct you to research, resources, and services. Many organizations also have experts who serve as medical advisors or provide lists of doctors/clinics. Visit the group’s website or contact them to learn about the services they offer. Inclusion on this list is not an endorsement by GARD.

    Organizations Supporting this Disease

      Organizations Providing General Support

        Learn more

        These resources provide more information about this condition or associated symptoms. The in-depth resources contain medical and scientific language that may be hard to understand. You may want to review these resources with a medical professional.

        Where to Start

        • Genetics Home Reference (GHR) contains information on Hereditary hyperekplexia. This website is maintained by the National Library of Medicine.
        • The National Organization for Rare Disorders (NORD) has a report for patients and families about this condition. NORD is a patient advocacy organization for individuals with rare diseases and the organizations that serve them.

          In-Depth Information

          • GeneReviews provides current, expert-authored, peer-reviewed, full-text articles describing the application of genetic testing to the diagnosis, management, and genetic counseling of patients with specific inherited conditions.
          • The Monarch Initiative brings together data about this condition from humans and other species to help physicians and biomedical researchers. Monarch’s tools are designed to make it easier to compare the signs and symptoms (phenotypes) of different diseases and discover common features. This initiative is a collaboration between several academic institutions across the world and is funded by the National Institutes of Health. Visit the website to explore the biology of this condition.
          • Online Mendelian Inheritance in Man (OMIM) is a catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
          • Orphanet is a European reference portal for information on rare diseases and orphan drugs. Access to this database is free of charge.
          • PubMed is a searchable database of medical literature and lists journal articles that discuss Hereditary hyperekplexia. Click on the link to view a sample search on this topic.


            1. Masri A, Chung SK, Rees MI. Hyperekplexia: Report on phenotype and genotype of 16 Jordanian patients. Brain Dev. April 2017; 39(4):306-311. https://www.ncbi.nlm.nih.gov/pubmed/27843043.
            2. Mine J, Taketani T, Yoshida K, et al. Clinical and genetic investigation of 17 Japanese patients with hyperekplexia. Dev Med Child Neurol. April 2015; 57(4):372-77. https://www.ncbi.nlm.nih.gov/pubmed/25356525.
            3. Lee Y, Kim NY, Hong S, et al. Familiar Hyperekplexia, a Potential Cause of Cautious Gait: A New Korean Case and a Systematic Review of Phenotypes. Journal of Movement Disorders. January 2017; 10(1):53-58. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5288664/.
            4. Tissen MAJ & Rees MI. Hyperekplexia. Gene Reviews. October 4, 2012; https://www.ncbi.nlm.nih.gov/books/NBK1260/.
            5. Haruno L. Hyperekplexia. National Organization for Rare Disorders (NORD). 2013; https://rarediseases.org/rare-diseases/hyperekplexia/.
            6. Mineyko A, Whiting S, Graham GE. Hyperekplexia: treatment of a severe phenotype and review of the literature. Can J Neurol Sci. 2011 May; 38(3):411-6. https://www.ncbi.nlm.nih.gov/pubmed/21515498.
            7. McAbee GN. Clobazam-clonazepam combination effective for stimulus-induced falling in hyperekplexia. J Child Neurol. 2015 Jan; 30(1):91-2. https://www.ncbi.nlm.nih.gov/pubmed/24453146.

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