Glycine is the smallest of the twenty amino acids commonly found in proteins. It’s one of the most widely distributed inhibitory receptors in the central nervous system and has important roles in a variety of physiological processes, especially in mediating inhibitory neurotransmission in the spinal cord and brain stem.
The glycine receptor is an ionotropic receptor that is constituted of 3 subunit-alfa and 2 subunit-beta: they constitute a permeable channel to the Cl, so it produces its effects through chloride current. The receptor can be activated not only by glycine, but also by alfa-alanine and taurine.
It can be blocked by strychnine
Hyperekplexia or startle is caused by defects in mammalian glycinergic neurotransmission, resulting in a complexmotor disorder characterised by neonatal hypertonia and an exaggerated startle reflex. This disorder affects newborn children and is characterised by noise or touch-induced non-epileptic seizures that result in muscle stiffness and apnea. Although rare, this disorder can have serious consequences, including brain damage and/or sudden infant death.
Genetic analysis of this disorder has revealed mutations in genes for several postsynaptic proteins involved in glycinergic neurotransmission, including the GlyR alfa1 and beta subunits , gephyrin and collybistin. The last two are some components of the postsynaptic protein network of inhibitory synapses.
However, new research suggests that mutations in the gene encoding the presynaptic glycine transporter GlyT2 are a second major cause of human hyperekplexia.
Mutations in GlyR subunit genes
Disease-Specific Human Glycine Receptor alfa1 Subunit Causes Hyperekplexia Phenotype and Impaired Glycine- and GABA-Receptor Transmission in Transgenic Mice