Antibodies to L-Type Calcium Channels in Amyotrophic Lateral Sclerosis

To the Editor: I was rather confused by the article by Smith et al. (Dec. 10 issue)¹ and the related editorial by Rowland². The authors suggest that high-titer antibodies to human motor-neuron voltage-gated calcium channels (VGCCs) present in patients with amyotrophic lateral sclerosis (ALS) cross-react with rabbit L-type VGCC epitopes. Skeletal-muscle L-type channels show only 15 to 45 percent homology with extracellular domains of neuronal L-type channels, and thus high titers are more likely to suggest a reaction to a primary muscle antigen³. The assay used for L-type VGCCs is novel in that it relies on a sandwich…