Hyperekplexia and stiff-baby syndrome: an identical neurological disorder?

Hyperekplexia (startle disease) is an unusual, familial, neurological disorder characterized by abnormally enhanced startle response, followed in most cases by momentary generalized muscular stiffness. These attacks may cause the patients to fall rigidly, while remaining fully conscious. Startle symptomatology has generally an onset in infancy and is often accompanied, during the first years of life, by rigidity, sleep myoclonus, motor delay, regurgitation and apneic spells, which may cause sudden death. Stiff-baby syndrome is a familial disorder characterized by marked rigidity, with neonatal onset and gradual reduction during infancy, regurgitations, motor delay and attacks of stiffness. We report 4 new cases of hyperekplexia from two different families and another infant with stiff-baby syndrome discussing clinical, electrophysiological and genetic aspects of both neurological disorders in relation to other reported cases. We suggest a continuum between these familial syndromes, which are often misinterpreted as epilepsy or other disorders.