C9orf72 and amyotrophic lateral sclerosis: For instance, NfL reduction in CSF correlates with tofersen’s pharmacodynamic effects in SOD1-ALS (Everett and Bucelli, 2024), while poly-glycine-proline (poly-GP) DPR levels serve as target engagement biomarkers in C9orf72 trials (Wilson et al., 2022).