In addition to dysregulation of glutamate levels in ALS patients, recent studies have also detected elevated levels of D-serine (Figure 3), an activator/co-agonist of the N-methyl-D-aspartate (NMDA) ionotropic glutamate receptor, in the spinal cord of both ALS patients and transgenic mice carrying the SOD1 G93A mutation [17–18]. The gene discussed is SOD1; the disease is amyotrophic lateral sclerosis.