Supplementary Information Methods To quantify the editing efficiency at the Q/R site of GluR2 mRNA, nested PCR for GluR2 was conducted after cDNA synthesis with the following primers: for the first PCR, hG2F1 (5'-TCTGGTTTTCCTTGGGTGCC-3') and hG2R1 (5'-AGATCCTCAGCACTTTCG-3'); for the nested PCR, hG2F2 (5'-GGTTTTCCTTGGGTGCCTTTAT-3’) and hG2R2 (5'-ATCCTCAGCACTTTCGATGG-3'). We confirmed that these primer pairs were situated in two distinct exons with an intron between them and did not amplify products originating from other GluR subunits (data not shown). The PCR products (182 bp) originating from completely edited GluR2 mRNA were digested into two bands (116 bp, 66 bp) with the restriction enzyme BbvI, whereas the products originating from unedited GluR2 mRNA were digested into three bands (81 bp, 66 bp, 35 bp). Thus, the editing efficiency of the partially edited GluR2 mRNA was calculated by the quantitative analysis of each fragment (116 bp, 81 bp, 66 bp, 35 bp) using a 2100 Bioanalyser (Agilent Technology). In order to show that the GluR2 mRNA, both edited and unedited, 1 was derived from single-neuron tissue and not from glial tissue, we confirmed the presence of microtubule-associated protein-2 (MAP-2) mRNA, coupled with the absence of glial fibrillary acidic protein (GFAP) mRNA in each RNA sample by a PCR method. The PCR primer sets were shown in Supplementary Table 1b. 2 Supplementary Table 1a. Profiles of the individuals analysed in this study Individual Sex/Age Disease (years) Duration of Postmortem illness (years) delay (hours) A1 M/79 ALS 2.0 15 A2 M/71 ALS 2.0 12 A3 F/24 ALS 0.7 4.5 A4 M/52 ALS 13.0 3 A5 F/79 ALS 1.5 10 D1 M/65 DRPLA 16 15 D2 F/47 DRPLA 26 812 C1 F/28 Hypovolemia from trauma ─ 17 C2 F/31 Hypovolemia from trauma ─ 6 C3 M/78 Heart failure, not otherwise specified ─ 12 C4 M/57 Hypovolemia from rupture of splenic ─ 17 ─ 28 artery, liver cirrhosis C5 F/27 Hypovolemia from trauma 3 Age, age of patient at death; A1-A5, individuals with amyotrophic lateral sclerosis (ALS); D1-D2, individuals with dentatorubral-pallidoluysian atrophy (DRPLA); C1-C5, normal controls with no neurological disorders. Supplementary Table 1b. Sequences of primers used for PCR Oligonucleotide sequence Amplified product length (bp) MAP-2 198 Forward primer 5’-CCAAGGAGTCTGATTGCAGGA-3’ Reverse primer 5’-CCTCAACCACAGCTCAAATGC-3’ GFAP 182 Forward primer 5’-CTTGCGGTCCCTTCTTACTCAC-3’ Reverse primer 5’-CTCAGTCAAAGCAGAGTGGGTG-3’ MAP-2, microtubule-associated protein-2 (GenBank accession no. NM031846); GFAP, glial fibrillary acidic protein (GenBank accession no. NM002055). 4