Hyperekplexia 2

Alternative Names

  • HKPX2
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WHO-ICD-10 version:2010

Diseases of the nervous system

Extrapyramidal and movement disorders

OMIM Number

614619

Mode of Inheritance

Autosomal recessive

Gene Map Locus

4q32.1

Description

Hereditary hyperekplexia (HH) due to deficiency of the beta subunit of the glycine receptor is a disorder of the inhibitory glycinergic neurotransmitter system.  It is characterized by an exaggerated startle response to sudden external stimuli.  Affected infants react with violent jerking to noise and touch, and exhibit sustained stiffening of the trunk and limbs, fist clenching, and trembling that may resemble seizures.  This condition may be fatal in some cases, where the exaggerated startle response may lead to prolonged breath holding.  The children display delayed achievement of motor milestones, although intellectual development is not affected.

Molecular Genetics

The glycine receptor is a pentamer composed of alpha and beta subunits, and is encoded by five different genes (GLRA1, GLRB, GPHN, ARHGEF9, and SLC6A5).  Mutations in both GLRA1 and GLRB have been reported to cause HKXP.  HKXP2 is caused due to mutations in the GLRB gene that codes for the beta subunits of the glycine receptor.  The beta subunit of the glycine receptor functions as a neurotransmitter-gated ion channel, which produces hyperpolarization via increased chloride conductance due to the binding of glycine to the receptor.

Epidemiology in the Arab World

View Map
Subject IDCountrySexFamily HistoryParental ConsanguinityHPO TermsVariantZygosityMode of InheritanceReferenceRemarks
614619.1.1Saudi ArabiaMaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 1' from 'Fa...
614619.1.2Saudi ArabiaFemaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 2' from 'Fa...
614619.1.3Saudi ArabiaFemaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 3' from 'Fa...
614619.1.4Saudi ArabiaFemaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 4' from 'Fa...
614619.1.5Saudi ArabiaMaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 5' from 'Fa...
614619.1.6Saudi ArabiaFemaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 6' from 'Fa...
614619.1.7Saudi ArabiaFemaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 7' from 'Fa...
614619.1.8Saudi ArabiaFemaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 8' from 'Fa...
614619.1.9Saudi ArabiaMaleYesYes Increased fetal movement; Abnormal muscl...NM_000824.5:c.596T>GHomozygousAutosomal, RecessiveAl-Owain et al. 2012 'Patient 9' from 'Fa...
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