Neurophysiological findings of the late-onset, dominant, proximal spinal muscular atrophies with dysautonomia because of the VAPB PRO56SER mutation.

The vesicle-associated membrane protein/synaptobrevin-associated membrane protein B (VAPB) Pro56Ser mutation has been identified in Brazilian families showing various motor neuron syndromes. However, the neurophysiological characteristics of these patients have not been detailed, and some questions still need to be solved, such as the possible presence of myotonia and the origin of the abdominal protrusion seen in most patients. The eventual finding of suggestive electrophysiological characteristics would be helpful not only for clinical diagnosis but also to selection of the appropriate DNA test. To clarify these questions we carried out sensory and motor conduction studies, including sympathetic skin response, and needle examination in six genetically proven affected members. The electromyographic findings were those of a slowly progressive motor neuron disorder. Topographically, the abdominal muscles were severely affected, but the facial and laryngeal muscles were preserved or very mildly involved. Sensory conduction studies and sympathetic skin responses were normal. No myotonic discharge was recorded. These findings are indistinguishable from those of other motor neuron disorders, although the predominant involvement of the proximal limbs and of the abdominal muscles may be of some help in the appropriate clinical setting.