We did observe a significant positive correlation between total serum MMP-9 levels and serum creatinine levels in ALS (Pearson’s p = 0.028, Spearman’s rank p = 0.005) that was not observed among HC (Pearson’s p = 0.77, Spearman’s rank p = 0.25). Here, MMP9 is linked to amyotrophic lateral sclerosis.