Abstract: The present invention relates to neurological and physiological dysfunction associated with neuron disorders. In particular, the invention relates to the involvement of vascular endothelial growth factor (VEGF) and homologues in the aetiology of motor neuron disorders. The invention further concerns a novel, mutant transgenic mouse (VEGFm/m) with a homozygous deletion in the hypoxia responsive element (HRE) of the VEGF promoter which alters the hypoxic upregulation of VEGF. These mice suffer severe adult onset muscle weakness due to progressive spinal motor neuron degeneration which is reminiscent of amyotrophic lateral sclerosis (ALS)—a fatal disorder with unknown aetiology. Furthermore, the neuropathy of these mice is not caused by vascular defects, but is due to defective VEGF-mediated survival signals to motor neurons.