Hyperekplexia

Clinic

• A very rare neurologic disorder classically characterized by pronounced startle responses to tactile or acoustic stimuli and hypertonia.
• The hypertonia may be predominantly truncal, attenuated during sleep and less prominent after a year of age.
• Classic hyperekplexia is caused by genetic mutations in a number of different genes, all of which play an important role in glycine neurotransmission.
• Glycine is used by the central nervous system as an inhibitory neurotransmitter.
• Hyperekplexia is generally classified as a genetic disease, but some disorders can mimic the exaggerated startle of hyperekplexia.

Signs and symptoms

The three main signs of hyperekplexia are

• Generalized stiffness
• Excessive startle beginning at birth
• Nocturnal myoclonus

• Affected individuals are fully conscious during episodes of stiffness, which consist of forced closure of the eyes and an extension of the extremities followed by a period of generalized stiffness and uncontrolled falling at times.

Other signs and symptoms include

• Episodic neonatal apnea
• Excessive movement during sleep
• Head-retraction reflex
• The link to some cases of Sudden Infant Death remains controversial.