SUMMARY The clinical features of two brothers and one nephew with X-linked recessive bulbospinal neuronopathy are described. The neurophysiological investigations and sural nerve biopsy, previously unreported, confirmed that both motor and sensory nerves are affected. Because of the genetic implications, the importance is stressed of recognising this disorder as a separate entity which should not be classified with the spinal muscular atrophies.In 1968, Kennedy and colleagues' reported II males from two families with a distinct form of bulbar and spinal muscular atrophy which was slowly progressive and inherited as an X-linked recessive. Since then a further 31 patients have been described in five separate reports,2 -6 ten being described by Harding and colleagues6 in 1982. As well as reporting similar findings to Kennedy's, they found reduced or unrecordable sensory nerve action potentials in seven patients and because of this abnormality they named it X-linked recessive bulbo-spinal neuronopathy.X-linked recessive bulbo-spinal neuronopathy is a slowly progressive disorder which develops between the third and fifth decades. Muscle wasting and weakness, which is often preceded by cramps for many years, commonly starts proximally in the limbs and then progresses to involve the masticatory, facial and bulbar musculature. Distal wasting and weakness occurs more commonly in the arms. Fasciculations are prominent in the peri-oral region and tongue as well as being generalised. Tendon areflexia is invariable at an advanced stage. A fine tremor of the outstretched hands may predate the onset of muscle weakness, gynaecomastia is a common finding and there is an increased incidence of diabetes mellitus, both in affected patients and in their first degree relatives. Patients have a normal life expectancy.We report three patients with this disorder (fig 1),

A pronounced 24-hour fluctuation occurs in the mitotically active tissues of the rat maxillary incisor. High and low periods of activity were seen during the daytime as well as at night. A consistent increase in the number of mitotic figures occurred approximately four hours subsequent to a change in the light-dark regimen.