Hyperekplexia (stiff baby syndrome, startle disease) is a genetic disease involving an abnormal gene for a subunit of the glycine receptor on chromosome 5q. Inheritance is autosomal dominant or sporadic. The hallmark of the disease is a triad of symptoms including general ized stiffness of the baby, particularly while awake, nocturnal myoclonus, and an exaggerated startle reflex. Upon awakening or with an auditory or tactile stimulus, the neonates and infants may have a marked generalized episode of stiffening associated with apnea. These episodes can be severe and cause hypoxic brain injury. Manual flexion of the neck and hips may resolve an episode. These episodes lessen in severity as the child grows older. As adults, the subject may have a pathologic startle response to even a minor visual, auditory, or tactile stimulus. Both clonazepam and val-proate have been cited in the literature as useful therapies (11,12) (see also Chapter 13).
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