Sera from patients with motor neuron disease and associated paraproteinaemia fail to inhibit experimentally induced sprouting of motor nerve terminals.

IgG kappa paraproteinaemia was discovered in one patient with amyotrophic lateral sclerosis and one with chronic spinal muscular atrophy. Serum from these patients was injected into mouse muscles paralysed by botulinum toxin which is known to induce sprouting from motor nerve terminals. Daily injection of serum for 7 days failed to inhibit terminal sprouting. It is concluded that the paraproteins did not recognise a growth factor postulated as being implicated in the pathogenesis of motor neuron disease.