HLA-DRB5 and amyotrophic lateral sclerosis: Previous reports showed that the HLA-DRA/HLA-DRB5 polymorphism affects the risk of developing sporadic ALS [34], while the loss of major histocompatibility complex (MHC) class 1 (corresponding to HLA in human beings) in motor neurons increased their vulnerability to astrocyte-mediated toxicity [35].