GRIA1 and amyotrophic lateral sclerosis: Given that excitotoxicity and altered cortical excitability are pathophysiological features associated with ALS [26], we next investigated the effect of the N533H and L534I mutants on the surface expression of the GluA1 and GluA2 subunits of AMPARs, which mediate the majority of fast excitatory synaptic transmission in the mammalian central nervous system [27].