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Hyperekplexia 1(STHE)

MedGen UID:
Concept ID:
Disease or Syndrome
Synonyms: GLRA1-Related Hyperekplexia; GPHN-Related Hyperekplexia; HYPEREKPLEXIA 1, AUTOSOMAL DOMINANT; HYPEREKPLEXIA 1, AUTOSOMAL RECESSIVE; Kok disease; Startle disease, familial; Startle reaction, exaggerated; STHE; Stiff-baby syndrome; Stiff-man syndrome, congenital; Stiff-person syndrome, congenital
Genes (locations): GLRA1 (5q33.1); GPHN (14q23.3-24.1)
Monarch Initiative: MONDO:0007868
OMIM®: 149400


Hyperekplexia is an early-onset neurologic disorder characterized by an exaggerated startle response to sudden, unexpected auditory or tactile stimuli. Affected individuals have brief episodes of intense, generalized hypertonia in response to stimulation. Neonates may have prolonged periods of rigidity and are at risk for sudden death from apnea or aspiration. Many affected infants have inguinal hernias. The symptoms tend to resolve after infancy, but adults may have increased startle-induced falls and/or experience nocturnal muscle jerks (summary by Ryan et al., 1992). Genetic Heterogeneity of Hyperekplexia See also HKPX2 (614619), caused by mutation in the GLRB gene (138492) on chromosome 4q31; HKPX3 (614618), caused by mutation in the GLYT2 gene (SLC6A5; 604159) on chromosome 11p15; and HKPX4 (618011), caused by mutation in the ATAD1 gene (614452) on chromosome 10q23. Hyperekplexia can also occur in developmental and epileptic encephalopathy-8 (DEE8; 300607), caused by mutation in the ARHGEF9 gene (300429). See also sporadic stiff-man syndrome (184850) and the 'Jumping Frenchmen of Maine' (244100). [from OMIM]

Additional description

From MedlinePlus Genetics
Hereditary hyperekplexia may explain some cases of sudden infant death syndrome (SIDS), which is a major cause of unexplained death in babies younger than 1 year.

The signs and symptoms of hereditary hyperekplexia typically fade by age 1. However, older individuals with hereditary hyperekplexia may still startle easily and have periods of rigidity, which can cause them to fall down. They may also continue to have hypnagogic myoclonus or movements during sleep. As they get older, individuals with this condition may have a low tolerance for crowded places and loud noises. People with hereditary hyperekplexia who have epilepsy have the seizure disorder throughout their lives.

Other signs and symptoms of hereditary hyperekplexia can include muscle twitches when falling asleep (hypnagogic myoclonus) and movements of the arms or legs while asleep. Some infants, when tapped on the nose, extend their head forward and have spasms of the limb and neck muscles. Rarely, infants with hereditary hyperekplexia experience recurrent seizures (epilepsy).

Hereditary hyperekplexia is a condition in which affected infants have increased muscle tone (hypertonia) and an exaggerated startle reaction to unexpected stimuli, especially loud noises. Following the startle reaction, infants experience a brief period in which they are very rigid and unable to move. During these rigid periods, some infants stop breathing, which, if prolonged, can be fatal. Infants with hereditary hyperekplexia have hypertonia at all times, except when they are sleeping.  https://medlineplus.gov/genetics/condition/hereditary-hyperekplexia

Clinical features

From HPO
MedGen UID:
Concept ID:
Very brief, involuntary random muscular contractions occurring at rest, in response to sensory stimuli, or accompanying voluntary movements.
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Sign or Symptom
A seizure is an intermittent abnormality of nervous system physiology characterized by a transient occurrence of signs and/or symptoms due to abnormal excessive or synchronous neuronal activity in the brain.
MedGen UID:
Concept ID:
Abnormally diminished motor activity. In contrast to paralysis, hypokinesia is not characterized by a lack of motor strength, but rather by a poverty of movement. The typical habitual movements (e.g., folding the arms, crossing the legs) are reduced in frequency.
Nocturnal seizures
MedGen UID:
Concept ID:
Disease or Syndrome
Seizures that occur while the affected individual is sleeping.
Exaggerated startle response
MedGen UID:
Concept ID:
An exaggerated startle reaction in response to a sudden unexpected visual or acoustic stimulus, or a quick movement near the face.
Inguinal hernia
MedGen UID:
Concept ID:
Protrusion of the contents of the abdominal cavity through the inguinal canal.
Umbilical hernia
MedGen UID:
Concept ID:
Anatomical Abnormality
Protrusion of abdominal contents through a defect in the abdominal wall musculature around the umbilicus. Skin and subcutaneous tissue overlie the defect.
Hip dislocation
MedGen UID:
Concept ID:
Injury or Poisoning
Displacement of the femur from its normal location in the hip joint.
MedGen UID:
Concept ID:
A condition in which there is increased muscle tone so that arms or legs, for example, are stiff and difficult to move.
Frequent falls
MedGen UID:
Concept ID:
MedGen UID:
Concept ID:
Sign or Symptom
Lack of breathing with no movement of the respiratory muscles and no exchange of air in the lungs. This term refers to a disposition to have recurrent episodes of apnea rather than to a single event.
MedGen UID:
Concept ID:
Inspiration of a foreign object into the airway.

Professional guidelines


Masri A, Chung SK, Rees MI
Brain Dev 2017 Apr;39(4):306-311. Epub 2016 Nov 11 doi: 10.1016/j.braindev.2016.10.010. PMID: 27843043
Thomas RH, Chung SK, Wood SE, Cushion TD, Drew CJ, Hammond CL, Vanbellinghen JF, Mullins JG, Rees MI
Brain 2013 Oct;136(Pt 10):3085-95. Epub 2013 Sep 11 doi: 10.1093/brain/awt207. PMID: 24030948
Chokroverty S, Walczak T, Hening W
Electroencephalogr Clin Neurophysiol 1992 Aug;85(4):236-42. doi: 10.1016/0168-5597(92)90111-n. PMID: 1380910

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