A 14-year-old girl with hyperekplexia having GLRB mutations.

Hyperekplexia manifests as generalized stiffness and an excessive startle reflex to stimuli. It starts in the neonatal period and is transmitted in many cases via autosomal dominant inheritance. The etiology is an abnormality of the glycinergic neurotransmission system that is involved in inhibitory neurotransmission. Aberrations of five genes related to this neurotransmission system have been identified. The patient was a 14-year-old girl with mild mental retardation. None of her family members had a neuromuscular disease. An excessive startle reflex and generalized stiffness were noted immediately after birth and she was diagnosed with epilepsy because epileptic discharges were observed. However, the disease was resistant to various antiepileptic drugs and the startle responses persisted. GLRB gene mutations (R50X/Q216fsx222) were identified, after which the patient was diagnosed with hyperekplexia. The startle reflex improved when clonazepam treatment was initiated. When patients have a persistent startle reflex, it is necessary to consider hyperekplexia, even if epileptic discharges are observed. Only four cases with GLRB mutations, including the present patient, have been reported. To make a definite diagnosis of hyperekplexia, it may be useful to screen for genes that are involved in the glycinergic neurotransmission system.