BDNF and amyotrophic lateral sclerosis: To explore relationships between expression of the 20 differentially expressed genes in C9-ALS-FTSD and disease progression, gene expression was correlated with disease duration and ALSFRS slope of decline, identifying a positive correlation between BDNF expression and disease duration (Spearman’s R = 0.64, P = 0.047) (Fig. 4A).