Hyperekplexia, Hereditary 1

Alternative Names

  • HKPX1
  • Startle Disease, Familial
  • Startle Reaction, Exaggerated
  • Exaggerated Startle Reaction
  • STHE
  • Stiff-Baby Syndrome
  • Stiff-Man Syndrome, Congenital
  • Stiff-Person Syndrome, Congenital
  • KOK Disease
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WHO-ICD-10 version:2010

Diseases of the nervous system

Extrapyramidal and movement disorders

OMIM Number


Mode of Inheritance

Autosomal dominant and autosomal recessive

Gene Map Locus



Hyperekplexia is an infantile-onset disorder characterized by an exaggerated startle response and intense, generalized hypertonia in response to sudden, unexpected auditory or tactile stimuli.  The disorder can be fatal in neonates as the prolonged periods of rigidity can lead to sudden death from apnea or aspiration.  Affected infants look alert, tense and frightened and may also suffer from congenital dislocation of the hip.  While hypertonia diminishes after the first year of life, patients suffer from startle-induced falls or nocturnal myoclonic muscle jerks.  Patients may also have umbilical and inguinal hernias and hyperactive brainstem reflexes such as head retraction, palmomental and snout reflexes.

Epidemiology in the Arab World

View Map
Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
149400.2SyriaMaleNoNo Seizures ; Exaggerated startle response... NM_000171.4:c.994G>AHeterozygousAutosomal, DominantWadi et al, 2018
149400.1United Arab EmiratesUnknown Global developmental delay ; Generalize... NM_000171.4:c.1214G>AHomozygousAutosomal, RecessiveAl-Shamsi et al. 2016
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