Startle epilepsy complicating Down syndrome during adulthood.

A woman with Down syndrome--a trisomy 21 karyotype--developed severe startle epilepsy and spontaneous seizures at the age of 20 years. Triggering factors, seizure patterns, and ictal electroencephalograms were the same as in startle epilepsy occurring in children with cerebral palsy but differed in that there was no clinical or radiological evidence of a focal brain lesion in the vicinity of the motor supplementary cortex. A therapeutic trial with clonazepam substantially reduced the frequency of reflex-induced and spontaneous seizures.