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The disorder was first discribed in 1958 by Kirstein and Silfverskiold, who reported a family with 'drop seizures'. In 1962 Drs. Kok and Bruyn reported an unidentifed hereditary syndrome, initially started as hypertonia in infants. The disease is responsible for Sudden Infant Death Syndrome in some cases.
The most prevalent symptom of hyperekplexia is an exaggerated startle response consisting of forced closure of the eyes and an extension of the extremities followed by a period of generalised stiffness similar to paralysis. It can be mistaken for cataplexy in narcolepsy sufferers.
The dominant form of hyperekplexia consists of an exaggerated startle response and stiffness possibly resulting in uncontrolled falling. Minor forms of hyperekplexia display an exaggerated startle response without the generalised stiffness.
The symptoms usually subside within the first year of life although it is not unknown for some symptoms to proceed into adulthood.
The cause of hyperekplexia is genetic. A mutation in the fifth chromosome (5q33.2-5q33.3) in the alpha-1 subunit of the glycine receptor is the most predominant cause of this neurological malfunction.
Mutations have also been discovered in the beta subunit gene (GLRB) (4q31) such as the point mutation G229D and within the glycine transporter 2 gene (GlyT2) (11p15)
An unverifiable link has been speculated between hyperekplexia and Asperger's Syndrome.
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