Major and minor form of hereditary hyperekplexia.

Hyperekplexia is a hereditary neurological disorder characterized by excessive startle responses. Within the disorder two clinical forms can be distinguished. The major form is characterized by continuous generalized stiffness in the first year of life and an exaggerated startle reflex, accompanied by temporary generalized stiffness and falls, whereas in the minor form only excessive startle and hypnic jerks have been described. Mutations in the gene encoding the alpha-1 subunit of the glycine receptor (GLRA1) are responsible for the major form of hyperekplexia but no mutation was detected in patients with the minor form in the large Dutch pedigree originally described by Suhren and colleagues. Here we describe the genetic analysis of the GLRA1 gene of two English families in which both forms of hyperekplexia were present. Mutation analysis revealed no genetic defect in the GLRA1 gene in patients carrying either the minor or major forms. This is further evidence that the minor form of hyperekplexia is seldom due to a genetic defect in the GLRA1 gene.