Acetylcholinesterase and ATPases in motor neuron degenerative diseases

Acetylcholinesterase (AChE) activity was measured in the presence of the specific inhibitor of pseudocholinesterase, iso-OMPA, in plasma from patients with amyotrophic lateral sclerosis (ALS), progressive muscular atrophy (PMA), neuromuscular disease controls, and normal controls. Both AChE and Na-K ATPase activities were measured in erythrocyte ghost membranes from ALS and normal controls. Activities of erythrocyte ghost AChE and Na-K ATPase did not differ between ALS and control patients, suggesting that erythrocyte membranes were normal in ALS. However, the activity of plasma AChE in patients with ALS and PMA was increased significantly over plasma activity in disease controls and normal controls. In addition, in an animal model of human PMA, the Wobbler mouse, plasma AChE activity was increased significantly over littermate controls. The explanation for the increase in plasma acetylcholinesterase was not clear; however, a number of potentially useful clinical points followed from this study. First, there was no relationship between a specific subtype of motor neuron disease and the level of AChE activity. Second, AChE activity appeared to vary directly with the duration of PMA but not with the severity of PMA. This did not correlate with either the duration or severity of ALS. Last, plasma AChE activity was normal in about 30% of patients who had motor neuron disease; therefore, AChE assay had limited use in the diagnosis of ALS or PMA.