Benign monomelic amyotrophies of upper and lower limb are not associated to deletions of survival motor neuron gene

Benign monomelic amyotrophies (BMAs) are rare conditions in which neurogenic atrophy is restricted either to the upper or lower limb. BMAs are usually sporadic, have insidious onset and slow progression followed by stabilization, are clinically confined for many years to a single limb and lack of sensory, bulbar, and pyramidal signs. Although the aetiology and pathogenesis of BMAs are unknown they are considered variants of spinal muscular atrophy with focal emphasis and a benign course. We studied 7 patients with BMAs to investigate whether they present alterations of the survival motor neuron gene (SMN) which has been found deleted or disrupted in proximal spinal muscular atrophy. All 7 patients showed the presence of both exon 7 and 8 of SMN gene. These findings indicate that deletions at the SMN locus are not present in BMA of upper and lower limb and suggest that these disorders are not only clinically but also genetically separate entities from proximal spinal muscular atrophies.