Abstract
1. The case is described of an eight-year-old girl with the Morquio syndrome (mucopolysaccharidosis type IV) who died from acute tetraplegia, due to atlanto-axial subluxation which occurred during general anaesthesia.
2. Hypoplasia of the dens of the axis vertebra entails a high risk of vertebral dislocation and spinal cord damage especially in circumstances such as general anaesthesia when excessive movements of the head may occur.