Weird Laughing in Hyperekplexia: A new phenotype associated with a novel mutation in the GLRA1 gene?

Hyperekplexia (HPX) or startle disease is a rare hereditary neurological disorder characterized by generalized stiffness, excessive startle reflex to unexpected stimuli and a short period of generalized stiffness following the startle response, and can be complicated by umbilical or inguinal hernia, developmental delay and apnea spell. HPX is caused mainly by mutations in the GLRA1 gene, and has a good response to clonazepam. In this short communication we describe an 11-year-old girl with excessive startle reflex, weird laughing and developmental delay since early infancy. She also suffered from infantile spasms and generalized tonic-clonic seizures, and became seizure-free with antiepileptic drugs treatment. However, the weird laughing was still present during the treatment. Her mother also appeared excessive startle reflex during early infancy. A novel mutation in GLRA1 was detected in the girl and her mother. Consequently, she was diagnosed with HPX, and clonazepam was added. The weird laughing was dramatic improved, which hasn't been reported in HPX. This is the first report of weird laughing in a hyperekplexia patient carrying a novel GLRA1 mutation, and expanded the phenotype spectrum of HPX.