We have recently identified mutations in pre-synaptic proteins shown to cause hereditary motor neuropathies, and have broadened the phenotypic spectrum of neuromuscular junction (NMJ) disorders. We identified that mutations in SYT2, a presynaptic protein involved in synaptic vesicle exocytosis at the NMJ result in early onset hereditary motor neuropathy and presynaptic myasthenic syndrome. We showed that administration of 3,4 diaminopyridine, influencing the presynaptic part of the NMJ result in electrophysiological and clinical benefit in 2 patients carrying SYT2 mutations. In addition, NMJ abnormalities have been demonstrated in another genetic neuropathy, due to mutations in the glycyl tRNA aminoacyl synthetase (GARS). NMJ maturation defects precede impaired lower motor neuron connectivity in mice carrying GARS mutations and highlight the neuromuscular synapse as an important site of early, selective pathology in GARS-related neuropathy. This project studies NMJ function in the GARSC201R mouse model by detailed methods. In addition, we will further characterise the molecular mechanisms of NMJ stabilisation by reproducing the experiments in nerve-muscle co-cultures.