Startle responses in hereditary hyperekplexia
M. A. Tijssen, L. M. Voorkamp, G. W. Padberg and J. G. van Dijk
Department of Neurology and Clinical Neurophysiology, Leiden University Hospital, the Netherlands.
BACKGROUND: Patients with hereditary hyperekplexia have excessive startle
responses that are accompanied by transient stiffness and also continuous
stiffness in infancy. A point of mutation has been identified for the major
form of hereditary hyperekplexia in the gene encoding the alpha 1 subunit
of the glycine receptor. OBJECTIVE: To measure startle reflexes and
autonomic responses in the major form of hereditary hyperekplexia in the
original Dutch pedigree. DESIGN: Startle reflexes and autonomic responses
were examined by administering 3 series of 20 auditory stimuli at intervals
of 10 seconds (90 and 113 dB) and 60 seconds (113 dB). SETTING: The
Department of Neurology and Clinical Neurophysiology at the Leiden
University Hospital, Leiden, the Netherlands. SUBJECTS: Nine patients with
the major form of hyperekplexia and 20 healthy controls. Of the 9 patients,
5 took medication. The patients are part of the Dutch hyperekplexia
pedigree. MAIN OUTCOME MEASURES: Startle responses were quantified with
latency periods and areas of electromyographic bursts of the orbicular
muscle of the eye, sternocleidomastoid and biceps muscles, and the thenar
muscles. Autonomic reactions were measured with psychogalvanic responses
and beat to beat changes of blood pressure and heart rate. RESULTS: The
electromyographic bursts of the 4 muscles occurred in similar order in both
patients and controls. The onset of the latency periods in the patient
group was significantly (P < .001) prolonged in patients who took
medication. Without medication, patients had shorter latency periods of the
sternocleidomastoid muscle (P = .003) than controls. The electromyographic
burst occurred significantly more often in patients than in controls (P
< .001). The areas of the bursts were significantly larger in patients
than in controls (P < .001); the degree of habituation was significantly
stronger in patients than in controls (P < .001). The amplitude of the
psychogalvanic response was increased in hyperekplexia, and the degree of
habituation was significantly weaker in patients than in controls. Blood
pressure and heart rate did not clearly react in either group. CONCLUSIONS:
Motor startle responses are stronger and show more habituation in patients
with hereditary hyperekplexia than in controls. The excessive responses
include the psychogalvanic response. Increased responses do not necessarily
indicate decreased habituation in hyperekplexia.
