Kok disease: A genetic disorder also known as hyperexplexia in which babies have an exaggerated startle reflex (reaction). This disorder was not recognized until 1962 when it was described by Drs. Kok and Bruyn as a disease with the onset at birth of hypertonia (stiffness), exaggerated startle response, strong brain-stem reflexes (especially head-r... Found on http://www.medterms.com/script/main/art.asp?articlekey=8298