When stratified by MND subtype (ALS, PLS, PMA), plasma PRPH concentrations were marginally lower in PLS and PMA (1.26 ± 0.45 ng/mL) than in ALS (1.53 ± 0.64 ng/mL); however, robust statistical comparison was not feasible because only four PMA cases were available. This evidence concerns the gene PRPH and amyotrophic lateral sclerosis.