Hyperekplexia

Hyperekplexia, whose name means exaggerated surprise, is a neurological disorder marked by a pronounced startle response to touch or sound, followed by a period of muscle stiffness known as hypertonia. The stiffness may mainly affect the trunk, tends to ease during sleep, and can become less prominent after the first year of life. Classic hyperekplexia is caused by genetic mutations in a number of different genes, all of which play an important part in glycine neurotransmission. Glycine is used by the central nervous system as an inhibitory neurotransmitter. The condition is generally classified as a genetic disease, and some other disorders can mimic the exaggerated startle of hyperekplexia without being the same condition.