Researchers at the ANZAC Research Institute (University of Sydney and Concord Hospital) have found the cause of a hitherto mysterious disorder causing degeneration of motor nerves that leads to severe muscle wasting in the limbs. The disease is manifest almost exclusively in men but inherited through their mothers as carriers, a pattern that arises because the disorder is linked to a gene on the X chromosome. Affected men cannot run properly and show loss of strength in the hands and feet becoming increasingly disabled through later life. The gene defect causes a slow, but progressive degeneration of the ends of the long motor neurons which drive the limb muscles.