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Startle has been described as a kind of response, usually myoclonic, to a sudden and unexpected stimulus and in most of the cases it is acoustic, though other sensory modalities can also be contributory. Exaggerated startle is a feature of some neurological and psychiatric conditions, whereas hyperekplexia is a syndrome characterized by brisk and generalized startle in response to trivial stimuli and they do not seem to habituate with repetitive stimuli. It is usually a genetically determined congenital problem or may be acquired. Hereditary hyperekplexia is seen shortly after birth and sudden stiffness of the trunk and limbs along with clenching of fists is the presenting feature and consciousness is retained. Sudden death from spasm in the larynx or cardiorespiratory failure constitutes life risk. Symptomatic hyperekplexia represents lesion in the brain stem. At least five genes are associated with hereditary hyperekplexia and the first gene implicated is the GLRA1 in chromosome 5Q33.1, which accounts for about 80% of cases. GLRA1 gene mutations, transmitted both as autosomal dominant and recessive trait, lead to the production of a receptor that cannot properly respond to glycine, the neuroinhibitor and therefore, there is reduced inhibition of exaggerated movements in the spinal cord and the brain stem.