Considering that fluctuating symptoms could be overlooked due to a marked weakness in ALS and that the specificity of the RNS test may be decreased, we recommend that in the context of ALS, the diagnosis of concomitant MG syndrome should thus be discussed only in the presence of suggestive clinical features (fluctuating symptoms and fatigability especially involved in ocular and/or bulbar regions) or autoimmune antibodies related to neuromuscular junction in addition to a positive response to cholinesterase inhibitors. The gene discussed is BCHE; the disease is amyotrophic lateral sclerosis.