Gephyrin (GPHN) is an organizational protein that clusters and localizes the inhibitory glycine receptor (GlyR) and GABAA receptors to the microtubular matrix of the neuronal postsynaptic membrane. Mice deficient in gephyrin develop a hereditary molybdenum cofactor deficiency and a neurological phenotype that mimics startle disease (hyperekplexia). In non-neuronal tissues, the encoded protein is also required for molybdenum cofactor biosynthesis. Two isoforms produced by alternative splicing have been described. The observed MW of Gephyrin is 93 kDa, larger than the predicated of 83 kDa, which may be due to the modifications on various phosphorylation sites.