Two Japanese families with hyperekplexia who have a Arg271Gln mutation in the glycine receptor alpha 1 subunit gene

We report two Japanese patients from two families with hyperekplexia who have a Arg271Gln mutation in the glycine receptor alpha 1 subunit gene. The clinical course of both patients was typical for hyperekplexia, characterized by neonatal hypertonia and exaggerated startle response, and which improved gradually with age. One was associated with umbilical hernia and hip dislocation, diagnosed at 11 months, while the other was diagnosed at 1 month. Both showed positive head retraction reflex. Four Japanese families have been reported as having hyperekplexia including our cases, of which three have shown the same missense Arg271Gln mutation, most frequently found in patients from Northern Europe and the United States.