SLC1A2 and amyotrophic lateral sclerosis: However, several studies revealed an absence of methylation in the promoter region of several ALS-related genes, such as SOD1, vascular endothelial growth factor (VEGF), and glutamate type I transporter (GLT1) (Morahan et al., 2007; Oates and Pamphlett, 2007; Yang et al., 2010).