Introduction: Hereditary hyperekplexia is a rare clinical syndrome typically characterized by sudden and generalized startle in response to trivial but unexpected tactile or acoustic stimulations. Typically it is accompanied by a temporally but complete muscular rigidly, and usually it manifests shortly after birth. Some affected infants die suddenly from lapses in cardiorespiratory function. Mental development usually is normal.
Aim: To summarize and update the molecular bases underlying the hereditary hyperekplexia syndrome.
Development: Approximately 30% of the individuals suffering hereditary hyperekplexia show mutations on a gene located on chromosome 5q32 with a dominant or recessive trait. This gene encodes the alpha subunit of the strychnine-sensitive glycine receptor, which plays a crucial role in inhibitory glycinergic neurotransmission that process sensory and motor information. About 70% of the patients with hyperekplexia do not show genetic defects in the glycine receptor gene; this suggested that additional genes might be affected in this disease. Recent studies have reveals that mutations in the neuronal glycine transporter GLYT2 are a second major cause of hyperekplexia.
Conclusions: Hereditary hyperekplexia is a complex genetic disease in which several genes can be implicated, all of them directly or indirectly involved in inhibitory glycinergic neurotransmission. Two major proteins involved in hyperekplexia are the strychnine-sensitive glycine receptor (GlyR) and the neuronal glycine transporter GLYT2. Implication of secondary additional accompanying or interacting proteins in glycinergic terminals are not ruled out.