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Hyperexplexia, also called hyperekplexia, is a neurological disorder characterized by an exaggerated startle response in situations of distress.
The disorder was first described in 1958 by Kirstein and Silfverskiold, who reported a family with ‘drop seizures’. In 1962 Drs. Kok and Bruyn reported an unidentified hereditary syndrome, initially started as hypertonia in infants.[1] The disease is responsible for Sudden Infant Death Syndrome in some cases.[1]It was confirmed as hereditary in 1990 by neurologist Dr. Angelika Hahn when a child was diagnosed within 48 hours of its birth of having hyperexplexia.
The most prevalent clinical sign 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 and possibly resulting in uncontrolled falling. It can be mistaken for cataplexy in narcolepsy sufferers.
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)
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