A newborn infant with neonatal sporadic hyperekplexia is reported from the Universita di Napoli Federico II, Italy. Hypertonia and generalized myoclonic jerks after stimulation, noted at 4 days of life, were associated with hypocalcemia. Treatment with calcium gluconate and vitamin D corrected the hypocalcemia, but muscle rigidity and jitteriness persisted. Startle responses were induced by tactile stimuli during sleep but, unlike most cases of hyperekplexia, not in response to tapping the tip of the nose. Hypertonia was relieved and startle responses were milder following treatment with clobazam. At 18 month follow-up, an apnea monitor was discontinued, but clobazam treatment (0.2 mg/kg/daily) was still required. [1]

COMMENT. Hyperekplexia, or ‘startle disease,’ of the newborn may occur in major or minor forms, sporadic or familial, with autosomal dominant inheritance, the gene located on chromosome 5q. A myoclonic response to a tap on the nose, hyperreflexia with sustained clonus, hypertonia, jitteriness, and sleep myoclonus are the characteristic manifestations of the major form. The startle response is unaccompanied by stiffness in the minor form. Recurrent apnea, feeding difficulties, choking, and sudden death are reported in some cases.

Packard AM, and Miller VS, of Dallas, TX, report two infants with hyperekplexia who responded to clonazepam (0.05 mg/kg/day), and review 19 reports of 36 families with 220 affected members [2]. Of the cases in the literature, 25 had feeding difficulties in infancy, 21 were apneic, and 10 died in the first year.

Tijssen MAJ et al of Leiden University Hospital, the Netherlands, measured startle reflexes in 9 patients, ages 29 to 66 years, with major hereditary hyperekplexia from the original Dutch pedigree described by Suhren O et al in 1966 [3]. Motor startle responses were more pronounced in patients with a history of major hereditary hyperekplexia than in controls and, contrary to previous reports, also showed more habituation. The authors suggest that cases showing nonhabituation to repetitive stimuli may not fulfill all criteria for the major form of the disorder.