The detection of active matrix metalloproteinase-9 (MMP-9) by ELISA (enzyme-linked immunosorbent assay) in serum from patients with ALS and Guillain-Barre syndrome and its correlation with nerve damage suggests that MMP-9 can be used as an early marker in both disorders [147, 148]. The gene discussed is MMP9; the disease is Guillain-Barre syndrome.