Sir.—In the article "Hereditary Stiff-Baby Syndrome" (Journal 1981; 135:909-911), Lingam et al described a family with an autosomal dominant disorder characterized by infantile stiffening and an abnormal startle response. Lingam and colleagues seem to have reported a previously described condition known as hyperexplexia or Kok's disease.1,2
In hyperexplexia, as in the family described by Lingam and associates, hypertonia in the affected neonate leads to hypokinesis and a "fetal position." The hypertonia lessens or disappears during sleep and with holding of the infant, and it completely disappears by 2 years of age. Sitting, walking, and other gross motor milestones are delayed because of the hypertonia. In addition, affected persons during infancy and throughout life have an exaggerated startle reaction that occasionally may produce a generalized hypertonic response and falling. These persons, while falling, have no loss of consciousness nor do they make any attempt to protect themselves from the